Separating Twins in Educational Settings: Zygosity, Conduct Problems and Emotional Symptoms as Predictors of Relationship Quality

Hila Segal¹, A. Knafo-Noam² and Adi Lipin¹

¹The Academic College of Tel Aviv-Yaffo, Israel, ²Hebrew University of Jerusalem, Israel

Introduction: The dilemma of whether to place twins in the same or in different classrooms concerns many parents and educators. We examined whether classroom separation predicts twin relationship quality and whether this link varies by zygosity, conduct problems, and emotional symptoms. Materials & Methods: Families of 1529 twin pairs — monozygotic (MZ: sharing 100% of their genes, N = 325) and dizygotic (DZ: sharing 50% of their genetic variation on average, N = 1204) — participated at least once when the twins were at ages 5, 6.5, and 8–9 years old. Both parents reported on twins’ closeness and conflict, conduct problems, emotional symptoms, and classroom placement (together all day, together only in afternoon daycare, or fully separated). Results: Compared with DZ twins, MZ twins displayed higher closeness and greater similarity in conduct and emotional problems. Zygosity was unrelated to placement until age 8–9, when opposite-sex DZ pairs were more often separated. Across measurement points, conduct problems and emotional symptoms related more strongly to conflict than to closeness. No main effect of separation emerged on the twins’ relationship quality; however, partial separation (meeting only in after-school care) consistently intensified conflict, especially among MZ pairs. Conclusions: Interpreting the findings through family-systems theory, social-comparison theory, attachment theory, and an evolutionary-psychology perspective underscores the complexity of deciding whether to separate twins at school. Rather than adopting a uniform policy, tailored approaches may optimize both social-emotional development and the twin relationship by addressing the unique needs and characteristics of each pair within educational settings.

‘I Felt My Twins Were Like a “Diagnosis” … There was a Lot of Fear Around It’: Listening to the Experiences of Multiple Birth Care: A World Café Method Study

E. Bailey¹, L. Hibberd¹, M. Burlingham¹, L. Alamad¹, N. Fenwick², V. Gilroy³, and F. Cowdell¹

¹The Elizabeth Bryan Multiple Birth Centre, Birmingham City University, Birmingham, UK, ²Twins Trust, Woking, Surrey, UK, ³Institute of Health Visiting, London, UK

Introduction: Multiple birth families experience pregnancy, birth and the early years in a different way from families who have one baby. Professional advice often lacks a multiple birth focus, leaving multiple birth families feeling overlooked. Our World Café project focused on experiences of the first 1001 days, a time crucial for child development and where parents meet a range of professionals and transfer between services. Materials & Methods: The World Café method is a structured conversational process for sharing knowledge, in which groups discuss topics at several small tables like in a cafe. Three family-friendly, and in-person World Cafés were held in different areas of England, allowing in-depth professional (n = 5) and family experiences to be shared (n = 7). Data, collected following informed consent, was subject to thematic analysis and findings related to the quality framework for maternal and newborn care (QFMNC). Ethical approval was obtained from the institutional ethics committee. Results: Themes included overwhelm and worry, balancing the emotional and practical complexities and needing to be prepared. Multiple-specific care, especially when this was personalized via a specialist care team, was valued. Fragmented care led to uncertainty and diminished experiences. Professionals described a ‘positive deviant’ approach to meeting parents’ needs within the confines of their roles. Conclusions: The World Café allowed professionals and parents to articulate ideas for how experiences for both giving and receiving care could be improved. Findings suggest the QFMNC, including the elements for women and children with complications is appropriate to benchmark care in multiple births.

Working With Multiple-Birth Families Requires Targeted and Specialized Knowledge and Evidence-Based Practices

Kristiina Heinonen¹, Tuulikki Trias², Jaakko Kaprio³ and Katri Vehviläinen-Julkunen¹

¹University of Eastern Finland, Department of Nursing Science, Kuopio, Finland, ²Lapsi Center, Barcelona, Spain, ³University of Helsinki, Institute of Life Science, HiLIFE, FIMM, Finland

Introduction: A multiple-birth family (MBF) is a family with special needs which relate to the greater risks during pregnancy and birth, the individuality of the children, the intertwin relationship and interactions in the family. There has been limited research on the specific knowledge and competencies that nurses have in MBF family nursing. Material and Methods: This cross-sectional mixed method study, forming part of the TWIN LIFE 2021-26 project, aimed to determine the sources of MBF knowledge and types of knowledge needed in nursing. The participants were nurses (n = 72) working in maternity and child health clinics (n = 33). The data were collected by questionnaire, analyzed statistically and by content analysis. Results: The nurses described how they lacked a holistic understanding in MBF nursing. Their education had focused on pregnancy and birth, and they lacked specialized knowledge such as taking care of multiples, intertwin relationships, and parenthood. The participants obtained knowledge from professional sources and work experience. Personal experience with multiples helped nurses to better understand such families. Most of the participants had searched for knowledge on the Internet and in books, but few of them mentioned evidence-based research and publications. Conclusions: Evidence-based knowledge and support for nurses in applying this knowledge in MBF nursing must be strengthened. The training received by nurses should provide them with competence and practical knowledge. Globally, further education is needed, as well as intervention and impact studies in the multiple-birth context.

More Guidance and Information Needed on Sleeping Challenges With Twins From Health Care Professionals

Lotta Parkkonen¹, Siiri Utriainen² and Kristiina Heinonen³

¹Family Support, Kuopio, Finland, ²University of Eastern Finland, Department of Technical Physics, Faculty of Science, Forestry and Technology, Kuopio, Finland, ³University of Eastern Finland, Department of Nursing Science, Kuopo, Finland

Introduction: A child’s sleep is individually influenced by factors such as health status, circadian rhythm, parenting, and light conditions. Sleeping problems with multiples are amongst the most stressful aspects for parents and multiple-birth family life. Material and Methods: The aim of this TWIN LIFE 2021-26 project study was to describe parents of twins (n = 15) and with one baby’s experiences of sleep in a 0- to 2-year-old child. Data were collected in 2024–2025 via thematic interviews and analyzed by inductive content analysis. The aim was to better understand how families with young children sleep and to identify what kind of targeted support and guidelines they need. Results: According to the parents, the sleep of a 0- to 2-year-old child is multidimensional. Families with twins often face unique challenges and sleep characteristics that differ from those with singletons. For participants, social media was a key source of information for families on sleep, the unique experience of each family in their situation, on the key link between sleep and the parent’s health and wellbeing. The practical help that families received was often perceived as insufficient and dismissive. The experience of exhaustion and fatigue was particularly pronounced among mothers of multiple families. Conclusions: Health care professionals need appropriate in-service training, particularly in relation to multiple-birth families. Future research is needed on the effectiveness of infant sleep interventions.

Mothers of Multiples Experiences With Cesarean Delivery

Maria Kääriä¹, Päivi Kankkunen² and Kristiina Heinonen²

¹University of Helsinki, Finland, ²University of Eastern Finland, Department of Nursing Science

Introduction: Childbirth is one of life’s most significant events and has a long-lasting impact on a woman’s life. Multiple pregnancies and births carry specific risks, and multiple births often occur via cesarean section. There is few research about the experiences of mothers of multiples who undergo cesarean sections. Materials and Methods: The aim of this TWIN LIFE 2021-26 project study was to describe mothers of multiples (n = 15) experiences of cesarean sections, preparation for the procedure, and recovery. Data were collected in 2024−2025 via thematic interviews and analyzed by inductive content analysis. Results: Mothers of multiples received varying levels of support and guidance from healthcare providers. Independent information-seeking, multiple-birth preparation courses, and peer support were considered important during the preparation phase. Cesarean sections were generally perceived as a safe, quick, and easy way to give birth. Some mothers received substantial support and assistance from the medical staff, while others felt they lacked professional care or empathetic encounters. The first meeting with their babies was a memorable moment for the mothers. Recovery includes painful surgical wounds, and the varying levels of support received from healthcare staff. Effective pain management and mobility facilitated recovery, while complications and a burdensome family situation hindrance. Conclusions: The results indicate that there is room for improvement in the healthcare system regarding individual guidance and support for mothers of multiples. Additionally, the competence of hospital staff in caring for multiple-birth families should be examined more closely.

Delta or Déjà Vu: Revisiting Antenatal Criteria for Twin Anemia Polycythemia Sequence

Stephanie Ernst¹, Lauren Nicholas² and Rebecca Fischbein³

¹Stichting TAPS Support, ²D’Youville University, Buffalo, NY, USA, ³North East Ohio Medical University (NEOMED), Rootstown, OH, USA

Introduction: Twin anemia-polycythemia sequence (TAPS) is a serious complication of monochorionic twin pregnancies. Although antenatal diagnosis is possible, clinical practice remains inconsistent due to varying diagnostic criteria. In 2019, a Delphi consensus study proposed a new staging system that reintroduced fixed MCA-PSV thresholds first suggested in 2006, despite evidence of more sensitive and validated delta-based criteria. Here, we present a comparative review of diagnostic models and their potential clinical consequences. Materials & Methods: We compared three key diagnostic models: fixed MCA-PSV cut-offs (>1.5/<1.0 MoM), delta MCA-PSV > 0.373 MoM (Tavares de Sousa et al., 2019), and delta MCA-PSV > 0.5 MoM (Tollenaar et al., 2019), using reported sensitivity, specificity, and implications for detection and decision making. Sample sizes and confidence intervals are as reported in the original studies. We also evaluated the diagnostic value of additional ultrasound markers including placental dichotomy, cardiomegaly, and starry-sky liver, which were published after the Delphi consensus but have since shown clinical relevance. Results: Fixed cut-offs showed the lowest sensitivity (46%) despite high specificity. Delta > 0.5 MoM improved sensitivity to 83%. All reported sensitivity, specificity, and related measures are drawn directly from the published studies referenced. Additional markers were present in 86% of confirmed TAPS cases, reinforcing their diagnostic value. Although stronger evidence existed, it was not adopted. Compared to other models, fixed cut-offs have the potential for higher rates false negative (missed) diagnoses, delays in care, and prevent parents from receiving timely, accurate information to make informed decisions about their pregnancies. These inconsistencies also complicate data collection and limit international research comparability. Conclusions: The criteria adopted through the 2019 Delphi study represent a diagnostic step backwards. Revising current antenatal TAPS guidelines to include validated delta thresholds and additional ultrasound markers is essential to improve diagnostic accuracy, support parents through critical decisions, and strengthen the quality and comparability of global research. This position is backed by published evidence.

Longitudinal Changes in the Genetic and Environmental Influences on the Obesity Measures Related DNA Methylation Changes: A 5-Year Twin Study

W. Gao, Y. Liu, X. Wu, H. Wang, M. Yu, Z, Pang, R. Hu, Y. Pang, C. Liao, D. Sun, T. Huang, C. Yu, J. Lv, W. Cao, K. Miao, X. Hong and L. Li, L

Peking University Health Science Center, Peking, China

Introduction: Reproducibility of obesity-related DNA methylation (DNAm) sites (CpGs) remains low across studies, and the genetic and environmental contributions to these CpGs and their associations with obesity need further investigation. Methods: We systematically searched PubMed, EMBASE, and the EWAS catalogue for previously reported CpGs associated with BMI, waist circumference (WC), and waist-to-hip ratio (WHR). Using data from 1074 twins in the Chinese National Twin Registry collected in 2013 and 2018, we conducted a validation analysis. Structural equation models (SEMs) were used to assess the heritability of these CpGs and changes over time. Bivariate SEMs were employed to examine the genetic/environmental influences on DNAm stability at obesity-related CpGs and the relationships between baseline obesity indicators and follow-up DNAm. Results: We included 28 studies providing 2597/953/26 CpGs for BMI/WC/WHR, of which 528/151/6 were validated in this study. The overall mean heritability of these CpGswas 0.34, decreasing from 0.38 at baseline to 0.31 at follow-up. Genetic correlations between baseline and follow-up methylation levels were high (mean = 0.73), whereas environmental correlations were relatively low (mean = 0.19). The longitudinal effect of obesity metrics on DNAm was small but consistent, both genetically and environmentally (mean = 0.08 and 0.06 respectively). Notably, the CpGs cg09142829 (CLEC4A), cg01565130 (MPZL1), cg11024682 (SREBF1), and cg06500161 (ABCG1) displayed the highest genetic correlations with obesity-related indicators over time. Conclusions: This study validated previously reported obesity-related CpGs, demonstrating that their longitudinal stability is primarily driven by genetic factors. However, their associations with obesity are mainly due to the direct effect of obesity, rather than genetic or environmental contributors.

Exploring the Impact of Ultra-Processed Food on Male Health and Sperm Epigenetic Profiles in Twins

V. George^1,2, J. M. Preston², Y. T. Wong¹, R. Barrès, I. R. McLachlan³ and J. M. Craig^1,4,6

¹IMPACT, The Institute for Mental and Physical Health and Clinical Translation, School of Medicine, Deakin University, VIC, Australia, ²Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Denmark, ³Hudson Institute of Medical Research, Centre for Endocrinology and Metabolism, Melbourne, Australia, ⁴Department of Paediatrics, The University of Melbourne, Melbourne, VIC, Australia, ⁵Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d’Azur, CNRS and Inserm, Valbonne, France, ⁶Murdoch Children’s Research Institute, The Royal Children’s Hospital, Melbourne, Melbourne, VIC, Australia

Introduction: In high-income countries, rates of male infertility are rising, in part due to falling sperm counts. In parallel, such countries are experiencing obesity pandemics. A common factor is the increased accessibility and consumption of ultra-processed food. Research has highlighted that paternal diet prior to pregnancy is associated with adverse health outcomes in offspring, with environment-induced epigenetic change in sperm being the proposed mediator. To bridge the current gap, we have investigated the effect of ultra-processed food diet on sperm quality and DNA methylation. In addition, we will explore changes to cardiometabolic and psychological health. Materials & Methods: Using the co-twin control study design, 8 male twin pairs (5 identical, 3 nonidentical) of reproductive age were recruited, and each pair was randomised to receive unprocessed or ultra-processed food for a 3-week period. Ethics was obtained from the Monash Human Research Ethics Committee (RES-22-0000-051A). Both diets were isocaloric and equal in macronutrient content, but the micronutrient content and sources of macronutrients were varied. Blood was collected for comprehensive testing, and body composition was measured using DEXA. Reproductive health was measured with basic semen analysis. All data were obtained at baseline and postintervention. Statistical significance was assessed using a paired t-test, with the level of significance p ≤ .05. DNA methylation of sperm is being analysed using Nanopore sequencing. Results: Comparing the response from the unprocessed to ultra-processed diet, cholesterol levels were significantly higher in the ultra-processed diet group (total cholesterol p = .02), and changes (not significant) to body mass were observed, mainly due to changes in fat mass in the ultra-processed diet group (p = .2). The two diets did not significantly change markers of sperm quality, but progressive sperm motility tended to decline in the ultra-processed diet group (p = .03). Comparison of changes in genome-wide of sperm DNA methylation is in progress. Conclusions: While the effect of ultra-processed food on sperm DNA methylation is still being investigated, this study, controlling for genetic background and for shared environment, supports that consumption of ultra-processed food is detrimental for several health outcomes, regardless of calories and macronutrient content. Promoting the consumption of minimally processed food may represent a preconceptional strategy to improve fertility.

The Development of Values: Longitudinal Insights From Early Childhood and Genetic and Environmental Contributions in a Twin Study

Ariel Knafo-Noam, Louise Twito-Weingarten, Tamar Machlev-Blank and Nizan Shoham

The Hebrew University of Jerusalem, Jerusalem, Israel

Introduction: Values — abstract, desirable goals — are important guides to attitudes and behavior. Despite their centrality in moral development, little is known about how values emerge. It is often assumed that values primarily form during adolescence through familial socialization. However, recent research suggests that value development begins earlier than adolescence. A twin design can also help assess the limit of socialization. This study examines values’ early development, their genetic and environmental origins, and their links to temperament. Materials & Methods: The Longitudinal Israeli Study of Twins, which tracked children from early childhood to adolescence. The sample included 939 children at age 3, with biannual follow-ups extending to age 17. Temperament was assessed using parent reports at seven time points from ages 3 to 17 (EAS, Buss & Plomin), while values were self-reported with the PBVS (Doering) and PVQ (Schwartz) starting at age 9. Results: Findings indicate significant mean-level changes in values from childhood to adolescence. Genetic modeling suggests that individual differences in value stability and change are partially heritable. Moreover, early childhood temperament predicts later values despite differences in raters and time elapsed. Follow-up longitudinal genetic analyses will investigate the genetic and environmental contributions to the association between early temperament and later values. Conclusions: The genetic and environmental contributions to values and temperament as an early predictor challenge the assumption that values develop mainly in adolescence, and the notion that they result from socialization. The results have implications for developmental psychology, twin studies, and interventions supporting early moral development.

Bridging the Gap: Peer Support for Families Navigating Complications and Loss in Multiples

Stephanie Ernst¹, Sharon Darke² and Suzie Scofield²

¹Stichting TAPS Support, the Netherlands, ²Footprints Baby Loss, UK

Introduction: Families facing complications or loss in multiple pregnancies encounter emotional and psychological challenges that clinical care alone does not address. Peer support refers to non- clinical guidance from individuals with lived experience, delivered through multiple birth organizations, condition-specific groups, and both online and in-person networks. While widely used in mental health and oncology, evidence-based peer support remains absent from structured care in multiples, leaving a critical gap in perinatal care. Materials & Methods: A proposed support model, the IMPACT model (Integrated Model for Peer Support Around Complications and Twin/Multiple Loss), was co-designed using community input, peer governance frameworks, and principles outlined in a published position paper. Key elements include safeguarding, responsible moderation, and lived experience expertise. Community reflection identified unmet needs for safe, structured peer support. Results: This model has not yet been trialled in a clinical setting. However, community feedback through discussions and written reflections highlighted reduced isolation, improved emotional resilience, and greater confidence navigating care when peer support is utilized. In one study, 74% of families expecting monochorionic twins used social media for guidance, yet clinician engagement remained limited. These outcomes mirror established findings in other fields, supporting the model’s relevance for multiples. Conclusions: Peer support remains a missing piece in care for families of multiples. The IMPACT model addresses this gap with a structure grounded in lived experience. Next steps include finding funding pathways, clinician collaboration, resource development, and evaluation via satisfaction and implementation data.

Genetic and Epigenetic Divergence in Monozygotic Twins: Implications for Forensic Analysis

K. Kapoor and M. A. Shukla

School of Forensic Sciences, National Forensic Sciences University, Gandhinagar, Gujarat, India

Introduction: Monozygotic twins (MZT) have long served as a model for understanding genetic and environmental influences on phenotype. MZT conceived naturally are rare; however, advancements in assisted reproductive technology (ART) have augmented their prevalence worldwide. Factors like ovarian stimulation, advanced maternal age, and zona pellucida modification influence the rate of twinning. Though MZT are considered genetically identical, emerging evidences suggests that they exhibit measurable genetic and epigenetic divergence, arising from de-novo mutations, somatic mosaicism, and differential epigenetic reprogramming. Individualization and identification of MZT in forensic casework has always been challenging, as the gold standard DNA profiling fails to differentiate them. Materials & Methods: A structured literature review of scientific studies addressing postzygotic genetic variations — including single nucleotide variants (SNVs), copy number variations (CNVs), and single nucleotide polymorphisms (SNPs), detectable by next-generation sequencing (NGS), and epigenetic divergence, with a focus on DNA methylation profiling was performed. Inclusion criteria encompassed reports of molecular discordance in MZT and their forensic investigations. Results: Genetic analyses reveal that MZT accumulate various mutations during early embryonic development, enabling discrimination by NGS. Epigenetic studies demonstrate that younger MZT exhibit minimal methylation differences, whereas older twins show substantial, locus-specific divergence. Combined genetic–epigenetic profiling outperforms single-modality approaches in simulated forensic casework, successfully differentiating MZT. Conclusion: Integrating advanced genetic and epigenetic markers into forensic workflows would enhance the ability to distinguish MZT in criminal investigations, paternity disputes, and identity verification. Further validation and standardization of such hybrid methodology is necessary to implement in routine forensic caseworks & to curate health and disease.

Exploring the Unique Child-Rearing Challenges Faced By Parents of Multiples

R. Tomizawa, Y. Ogata and Y. Yokoyama

Graduate School of Nursing, Osaka Metropolitan University, Osaka, Japan

Introduction: The demands of parenting multiples are known to cause significant stress, often leading to extreme fatigue, sleep deprivation, and a lack of personal time. These stressors may also increase the risk of issues such as unequal treatment among siblings or emotional neglect. Child-rearing support tailored to families with multiple births varies significantly across regions. This study aimed to investigate the specific parenting challenges encountered by these families, based on data from a nationwide survey conducted during the COVID-19 pandemic. Materials & Methods: In January 2021, 1218 parents of multiples voluntarily responded to a nationwide survey by an NPO. Online consent was obtained. Free-text responses from 937 participants about child-rearing concerns were analyzed using content analysis by three researchers to ensure reliability. Results: Content analysis identified key challenges including a shortage of childcare support, sleep deprivation, emotional instability leading to anger toward children or partners, feelings of inadequacy in managing household tasks, and difficulties associated with going out. Conclusions: As the ages of children varied, the findings provide a broad overview of the challenges in raising multiples, suggesting that these difficulties are not solely attributable to the COVID-19 pandemic. This study revealed that, using free-text responses, parenting challenges were often described not simply as a lack of resources, but as feelings of inadequacy or regret about not meeting personal or societal expectations.

Exploring Parent-Child Relationships Among Twins and Their Mothers

B. Herath and X. Zhang

College of Health Solutions, Arizona State University, Phoenix, AZ, USA

Introduction: Twins offer a unique opportunity to examine the influence of genetics and environment on health/behaviors. While much research emphasizes genetics, the social environment, particularly the family, plays a central role in shaping child development. Adolescence is a critical period which maintaining parental closeness can be challenging. Studies show adolescents generally report stronger attachment to mothers than to fathers. In twin families, both children may be treated as a unit, which may influence their individual relationships with parents. Existing studies often rely on parental perspectives and focus on younger twins, offering limited insight into how adolescent twins perceive these relationships. This study examines how being a twin influences maternal-child closeness during adolescence, using data from a nationally representative U.S. sample. Materials & Methods: Data were drawn from the National Longitudinal Study of Adolescent to Adult Health (Add Health) with 20,745 respondents from Grades 7–12 during the 1994–95 school year, along with one parent. Linear regression models will be used to examine predictors of maternal closeness — the dependent variable. Independent variables include maternal factors (age at child’s birth, marital status, family structure, education, employment, and presence of other children) and child-specific factors (twin zygosity, gender, academic performance, closeness between twins, and frequency and satisfaction with communication with the mother). Results: Data analysis is ongoing. The sample includes 784 twins (289 monozygotic, 452 dizygotic). Preliminary expectations suggest both maternal and child factors will significantly influence perceived maternal closeness. Conclusions: Findings will offer insights into family dynamics in twin households and inform future family-based interventions aimed at strengthening maternal-child bonds during adolescence.

A Novel Polygenic Risk Score (PRS-) Informed Twin Study Reveals Limited Role of Genetic Predisposition on BMI

Tianyu Zhu^1,2,3, Gabin Drouard², Aino Heikkinen², Teemu Palviainen², Jaakko Kaprio², Robin Cristofari³ and Miina Ollikainen^1,2

¹Minerva Foundation Institute for Medical Research, Helsinki, Finland, ²Institute for Molecular Medicine Finland FIMM, HiLIFE, University of Helsinki, Helsinki, Finland, ³Institute of Biotechnology, HiLife, University of Helsinki, Helsinki, Finland

Introduction: Body Mass Index (BMI) is strongly influenced by genetics, yet lifestyle and environmental factors can create discrepancies between observed and polygenic risk score (PRS) predictions. We investigated multi-omics signatures associated with these mismatches in BMI-discordant twins. Materials & Methods: Using the Finnish Twin Cohort data, we calculated BMI residuals (measured BMI regressed on PRS, adjusted for age/sex). We compared the multi-omics profiles in BMI-discordant twin pairs where one twin’s BMI aligned with their PRS prediction, and the other was either above (Group A, N = 122 pairs) or below (Group B, N = 109 pairs) their predicted range. Results: Group A showed elevated ASAT levels (indicating liver damage), but no differences in epigenetic aging were detected. Most omics measures did not differ significantly between groups. Conclusions: We did not observe differences between two groups in most of the measurements, underlining the limited contribution of PRS in shaping individual response to high BMI. The results support broader applications of twin studies in precision health research.

Reared-Apart Twins: General Intelligence and Human Figure Drawings

Nancy Segal

California State University, Department of Psychology, Fullerton, CA, USA

Introduction: Psychological investigators and practitioners have been interested in the agreement between IQ scores from human figure drawing tasks and standard general intelligence tests. Some previous studiesreported associations between drawing performance and motor skills, but few studies have found meaningful relationships with cognitive ability. More importantly, few twin studies have considered a genetic component contributing to scores on drawing tests. The present study is the first to undertake these analyses using adult reared-apart twins. Materials and Methods: Wechsler IQ scores and drawing-derived IQ scores were available for reared-apart monozygotic (MZA, N = 71) and reared-apart dizygotic (DZA: N = 53) twin pairs from the Minnesota Study of Twins Reared Apart (MISTRA). Results: Intraclass correlations for the drawing derived performance scores were modest, albeit significantly higher for MZA (r _i = .31, p < .01) than DZA twin pairs (r _i = .02, ns), p < .001. Intraclass correlations for the Draw-a-Person IQ score (DAP:IQ) followed the same pattern. The correlation between the drawing-derived IQ scores and Wechsler IQ scores was very small with a low effect size, but statistically significant (r = .15, p = .02). Conclusion: The present findings suggest modest genetic influence on drawing performance.

The Experiences and Needs of Multiple Birth Fathers During the Early Years: Engagement With Fathers and Charities

L. Hibberd, M. Burlingham and L. Bailey

Elizabeth Bryan Multiple Births Centre, Birmingham City University, Birmingham, UK

Introduction: The early years of a child’s life are crucial for lifelong wellbeing, with parental relationships being incredibly formative. While father involvement positively impacts children’s development, research on fathers’ experiences remains limited, particularly for multiple birth fathers. Given the unique challenges multiple birth families face, understanding fathers’ experiences is essential for developing appropriate support services. Materials & Methods: An anonymous open-ended survey was distributed through the UK-based Twins Trust – Dads of Multiples Facebook group to explore fathers’ lived experiences during the early years (106 respondents [(6 triplet and 100 twin dads], aged 26−54). Data were analysed using inductive Thematic Analysis with NVivo. Ethical approval was granted from the relevant Birmingham City University Ethics Committee and informed consent was given by all. Results: Four main themes emerged: ‘the complexities of early multiple birth fatherhood’, ‘mental health’, ‘visibility of needs’, and ‘meeting the support needs’. All the respondents juggled emotional, practical, and financial demands while experiencing impacts on mental health and identity. All reported a support gap, with inconsistent services across localities and limited recognition of their unique challenges in healthcare, personal relationships, and workplaces. Social and peer support was valued. Conclusions: Multiple birth fathers face complex challenges requiring targeted support. Key needs include stronger support networks, flexible work arrangements, and greater recognition in healthcare settings. We suggest policy changes to address mental health during the perinatal and early years period, extend paternity leave and recognition of financial burdens. We highlight the importance and utilization of Twins Trust’s Dads Peer Support Service.

Twin Research: International Comparison of the Impact of Visceral Fat on Lifestyle Disease Risk in Japan and Hungary

Y. Arakawa¹, D. Matsumoto², F. Inu³, A. D. Tarnoki⁴, D. L. Tarnoki⁴, Osaka Twin Research Group¹ and M. Watanabe^1,5

¹Center for Twin Research, Graduate School of Medicine, The University of Osaka, Osaka, Japan, ²Department of Physical Therapy, Faculty of Health Sciences, Kio University, Kio, Japan, ³Department of Nursing Science, Faculty of Health Care, Tenri University, Tenri, Japan, ⁴Medical Imaging Centre, Semmelweis University, Budapest, Hungary, ⁵Division of Health Sciences, Graduate School of Medicine, The University of Osaka, Osaka, Japan

Introduction: Japan and Hungary present distinct patterns in visceral fat distribution and lifestyle disease prevalence. Japanese individuals tend to accumulate visceral fat even when BMI is low. Meanwhile, Hungary has high obesity and cancer mortality rates. This study compared visceral fat and clinical values of lifestyle diseases between both countries to clarify ethnic differences in obesity risk. We also evaluated genetic and environmental influences of visceral fat on clinical values using individual-based and within-pair regression analyses in monozygotic (MZ) twins. Materials & Methods: We studied 155 Hungarian and 163 Japanese MZ pairs. Clinical data included visceral fat, BMI, glucose and lipid markers, blood pressure. Differences between two independent groups were evaluated using Student’s t-tests or Wilcoxon tests. Intraclass correlation coefficients (ICCs) assessed twin concordance. Multiple regression analyses were performed at individual and within-pair. Results and Discussion: Hungarian twins had higher BMI and lipid markers, consistent with higher obesity prevalence. Japanese males had greater visceral fat despite lower BMI, indicating ethnic susceptibility. ICCs for all traits except HDL-C were higher in Hungarian twins, suggesting stronger genetic influences. Visceral fat showed genetic associations with glucose and HbA1c in Hungarian females, and with HDL-C in Japanese females. Conclusions: Japanese individuals, especially males, may be more susceptible to environmental influences on visceral fat. Genetic influence of visceral fat on clinical values was characteristic of each country: glucose metabolism in Hungarian females and lipid metabolism in Japanese females. These findings underscore the importance of personalized obesity prevention strategies tailored to genetic backgrounds.

Fertility Patterns Across Generations in Monozygotic and Dizygotic Twins Compared to Non-Twin Controls: Evidence From The Finnish Twin Cohort

S. Niemi de Paiva^1,2, M. Hukkanen¹, J. Kaprio¹ and S. Zellers¹

¹Institute for Molecular Medicine Finland, University of Helsinki, Finland, ²Gillings School of Public Health, University of North Carolina at Chapel Hill, USA

Introduction: While dizygotic (DZ) twinning is linked to heritable hyperovulation, less is known about whether twin status and zygosity predicts long-term reproductive outcomes in twins and their children. This study aims to identify fertility trends among twins and their descendants. Methods: We analyzed fertility outcomes from monozygotic (MZ, N = 4068), same-sex dizygotic (SSDZ, N = 8,890), opposite-sex DZ (OSDZ, N = 8474) twins born between 1945–1957 from the Finnish Twin Cohort and singleton population controls (N = 1,193,404) born the same years (total N = 1,214,836; 49.1% female). Population registers provide information on the number of biological children, biological grandchildren, age at first birth, and occurrences of multiple births. The preregistered analysis plan is available at https://osf.io/qbwv3. Results: Preliminary results on the number of biological children indicate significant variation across zygosity groups and sexes (males: F = 2.60, p = .051, females: F = 10.99, p = 3.26x10^-7). In other words, the effect of twin status and zygosity on fertility varies by sex; there was no effect of twin status or zygosity on number of children for males, but there was for females. Within females, OSDZ twins had the highest mean number of biological children (M = 1.86, SD = 1.36), followed by singletons (M = 1.80, SD = 1.32), SSDZ (M = 1.76, SD = 1.36), and MZ (M = 1.68, SD = 1.33). Additional analyses are ongoing to investigate intergenerational effects and potential moderating factors. Conclusions: These insights emphasize the importance of large twin cohorts in reproductive and population health research, with implications for understanding genetic and familial patterns in fertility, as well as generalizability between twins and singletons.

Better Twin Anemia Polycythemia Sequence (TAPS) Care Begins With Collaboration and Family-Centered Care

Stephanie Ernst¹ and Emilie L. Martinez²

¹Stichting TAPS Support, ²The Kaiden Paul Foundation

Introduction: Twin anemia polycythemia sequence (TAPS) is a serious complication that can affect monochorionic twin pregnancies worldwide. It occurs either spontaneously or as a complication following fetoscopic laser surgery for TTTS. While the condition is known globally, there are no unified screening protocols or long-term management guidelines. As two parents with different experiences of TAPS, we share how these inconsistencies create confusion, trauma, and gaps in care. Materials & Methods: This abstract is grounded in lived experience and insights gained through advocacy work. Data and observations are drawn from the TAPS Registry, which includes input from 17 fetal therapy centers on three continents, highlighting the differences in how spontaneous and post-laser TAPS are diagnosed and managed. Results:

Post-laser TAPS is often monitored in centers familiar with TTTS follow-up, yet screening and intervention strategies vary widely. Spontaneous TAPS is even less consistently recognized, with many centers not screening at all. Staging systems are not universally accepted, and long-term follow-up is inconsistent. Currently, treatment after diagnosis lack evidence-based guidelines. Families often navigate critical decisions without clear or consistent medical information, leading to distress and preventable harm. Conclusions: TAPS is not a rare local complication. It is a global condition that demands a coordinated international response. Standardized screening shared diagnostic criteria, and a commitment to collaboration across borders will help ensure that families receive the care they need, regardless of where they live. Including the parental voice in shaping this future is not optional, but essential.

Neurodevelopmental Outcome in Monochorionic Twins With Selective Fetal Growth Restriction Versus Uncomplicated Monochorionic Twins: An International Prospective Cohort Study

Jip A. Spekman¹, Silvana Arduino², Marina Balestriero³, Daniela Casati⁴, Caterina Colombo⁵, Davide Ferri⁶, Sophie G. Groene¹, Mariano Lanna⁴, Gianluca Lista⁵, Enrico Lopriore¹, Chiara Peila⁶, Tesse E. van Poppel¹, Barbara Scelsa³, Femke Slaghekke⁷ and Jeanine M. M. van Klink¹

¹Division of Neonatology, Department of Pediatrics, Willem-Alexander Children’s Hospital, Leiden University Medical Center, Leiden, the Netherlands, ²Gynaecology and Obstetrics 2U, Sant’Anna Hospital, Azienda Ospedaliero Universitaria Città della Salute e della Scienza di Torino, University of Turin, Turin, Italy, ³Department of Pediatric Neurology and Psychiatry, V. Buzzi Children’s Hospital, Milan, Italy, ⁴Fetal Therapy Unit ‘U.Nicolini’, V. Buzzi Children’s Hospital, Milan, Italy, ⁵Division of Neonatology and Neonatal Intensive Care Unit, V. Buzzi Children’s Hospital, Milan, Italy, ⁶Neonatal Unit, Department of Public Health and Pediatrics, University of Turin, Turin, Italy, ⁷Division of Fetal Medicine, Department of Obstetrics and Gynecology, Leiden University Medical Center, Leiden, the Netherlands

Introduction: In monochorionic twins with selective fetal growth restriction (sFGR), the smaller twin is at an increased risk for neurodevelopmental impairment (NDI). Existing literature is limited to relatively small studies comparing the smaller twin to either its larger co-twin or growth-restricted singletons. This study aimed to compare long-term neurodevelopmental outcomes at two years of age between the smaller twin in sFGR cases and twins from uncomplicated monochorionic twin pregnancies. Materials & Methods: Follow-up data from three prospective cohorts of monochorionic twins (2019−2023) will be aggregated, including in Leiden (the Netherlands), Milano, and Turin (Italy). sFGR is defined as an estimated fetal weight discordance ≥20% with an estimated fetal weight of the smaller twin <p10, and/or a birthweight discordance ≥20%. Uncomplicated twins had a birthweight discordance <20% and no other monochorionic twin-specific complications. Neurological, cognitive, and motor development were assessed using the Bayley-III and Griffiths-III scales. The primary outcome is the incidence of NDI, subdivided into mild to moderate (a cognitive, motor and/or general development score <85, minor neurological dysfunction or cerebral palsy grade 1, and/or mild visual or hearing impairment) and severe NDI (a cognitive, motor and/or general development score <70, severe neurological dysfunction, and/or severe visual or hearing impairment). Results: Upon completion of data collection, analyses will include a within-pair comparison of NDI in sFGR twins and a comparison with the control group of uncomplicated monochorionic twin pairs. Additionally, stratification by sFGR type and risk factor analysis for factors associated with NDI, including obstetrical and neonatal characteristics, will be performed.

Genetic and Environmental Contributions to Moral Foundations

T. Kawamoto¹, C. Shikishima² and J. Ando¹

¹Faculty of Letters, Keio University, Keio, Japan, ²Faculty of Letters, Teikyo University, Teikyo, Japan

Introduction: According to the moral foundations theory (Atari et al., 2023), human beings possess the following six moral domains: the intuitions to avoid emotional and physical harm to others (Care); the intuitions that individuals should be treated equally and receive equal outcomes (Equality); the intuitions that individuals should be rewarded according to their effort and contribution (Proportionality); the intuitions related to cooperation with one’s ingroup and competition with outgroups (Loyalty); the intuitions related to obedience to legitimate authority and the defense of traditions (Authority); and the intuitions related to avoiding physical and spiritual contamination or corruption (Purity). There is a lack of research that examines the genetic and environmental foundations of those moral foundations; thus, the present research aims to investigate it. Materials & Methods: A total of 407 adolescent twin pairs (160 monozygotic twins and 247 dizygotic twins) answered the online questionnaire, including the Moral Foundations Questionnaire–2 (MFQ–2: Atari et al., 2023) in March 2024. We applied a univariate genetic model to each MFQ–2 subscale score that was adjusted for the twins’ age and gender. Results: Results showed that approximately 30–40% of the variances of all MFQ–2 scores except for the purity foundation were explained by genetic factors. The heritability estimate of purity was lower than the others (h ² = 20%). No-shared environmental factors explained the remaining variances. Conclusions: These findings imply that genetic factors provide the stable underpinning of moral development and that individual external experiences may more influence the purity foundation.

Psychotherapeutic Care for Twins at the State University of Londrina, Brazil

Maria Elizabeth Barreto Tavares dos Reis

Universidade Estadual de Londrina, Brazil

Introduction: Twin pregnancies, considered high risk, require special care for the pregnant woman. Each twin shares the uterus with their sibling, so they always share physical and emotional space with their co-twin. At birth, basic needs are not always adequately met because the mother must share the care of both twins. As a result, twins may face more frustrations and emotional difficulties than singletons (when a single baby is born at birth). Aim: to describe the care provided to twins and their families through psychoanalytic psychotherapy at the State University of Londrina, Brazil. Materials & Methods: the study is part of a research project whose team is made up of psychologists, undergraduate and postgraduate psychology students. The participants are pregnant twins, twins and/or their families, and their respective psychotherapists. The brief psychoanalytic psychotherapy sessions take place at the university’s Psychological Clinic. After each session, the psychotherapist in charge draws up a clinical report. The reports are then analyzed by the project’s researchers. The clinical facts detected during the sessions are analyzed using the foundations of psychoanalysis. Results: Among the most frequent clinical facts, the following stand out: emotional and marital problems experienced by the pregnant women; difficulties relating to the twins’ self-image; jealousy; intra-twin competition; family, friendship and romantic relationship problems. Conclusion: the study highlights the need for psychoprophylactic and remedial care for the emotional problems experienced by twins.

The Etiology of Associations Between Interpersonal Violence, Depression and Suicidal Ideation in Colombo, Sri Lanka: Population-Based Twin and Singleton Study

Filip Marzecki^1,2, Yasmin I. Ahmadzadeh², Kaushalya Jayaweera³, Fruhling Rijsdijk⁴, Sisira Siribaddana⁵, Athula Sumathipala³, Binoli Herath³, Sameeha Jabir³, Kennath Widanaralalage¹, Isabella Badini⁶ and Helena M. S. Zavos¹

¹Department of Psychology, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK, ²Social, Genetic & Developmental Psychiatry Centre, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK, ³Institute of Research and Development in Health and Social Care in Sri Lanka, Sri Jayawardenepura Kotte, Sri Lanka, ⁴Anton de Kom University of Suriname, Paramaribo, Suriname, ⁵Rajata University of Sri Lanka, Mihintale, Sri Lanka, ⁶Division of Psychiatry, UCL, London, UK

Introduction: Interpersonal violence (e.g., bullying, intimate partner violence) affects millions of people worldwide and is related to mental health problems. However, research methodologies that allow us to study mechanisms of this association, such as longitudinal and twin studies, overrepresent populations in the global north. Methods: The Colombo Twin and Singleton Study collected data between 2005−2007 as well as 2012−2015. Analyses were conducted on participants who took part in both the first and the second data collection waves (N twins = 2849, N singletons = 1027). Linear models were used to assess correlates of interpersonal violence in 2012−2015, and quasi-causal monozygotic twin differences design was used to test the associations between interpersonal violence and mental health (depression and suicidal ideation). The classical twin model was applied to investigate gene-environment interactions. Results: There was a heightened risk of experiencing interpersonal violence among Sri Lankans previously affected by armed conflict or natural disasters, in men and those of lower socioeconomic status. Experiencing interpersonal violence was related to more depression symptoms after accounting for confounding familial factors, and it moderated the genetic and non-shared environmental influences on depression symptoms. Conclusions: Exposures to natural disasters and civil conflict are associated with a long-term increase in the risk of experiencing interpersonal violence. Being affected by interpersonal violence may be causally linked to depressive difficulties, and those with past vulnerabilities (genetic and environmental) may be more likely to be negatively affected.

Research on Self-Concept in Twins Aged 11–15 in the Czech Republic

Klára Kargerová¹, Leona Hozová² and Martin Dolejš³

¹Charles University, Prague, Czech Republic, ²Silesian University, Gliwice, Poland, ³Palacký University, Olomouc, Czech Republic

Introduction: This research aims to explore differences in self-concept between monozygotic (MZ) and dizygotic (DZ) twins aged 11–15 in the Czech Republic. While previous studies in South Korea and the USA have examined self-concept in twins, this is the first study of its kind conducted within this age group in the Czech Republic. Understanding self-concept differences between MZ and DZ twins may provide valuable insights for educational and psychological support tailored to twins. Materials & Methods: The study utilized a mixed-method approach, combining a standardized questionnaire developed by Dr M. Dolejš with focus group discussions. The questionnaire measured various aspects of self-concept, and data were collected from twins aged 11–15. Comparative analysis with international studies from South Korea and the USA was performed, acknowledging methodological differences. Results: The findings indicate an insignificant difference in self-concept between MZ and DZ twins, consistent with previous research from South Korea and Minnesota. This study provides the first data on twin self-concept within this age group in the Czech Republic. Conclusions: The results suggest that self-concept development in twins is largely consistent across different cultures and methodologies. Further research could involve comparing twins with singletons of the same age group using identical methodologies in the Czech Republic. These findings may guide educators, psychologists, and parents in providing appropriate support for twins.

Between Motherhood and Survival: Multiple Birth Caregiving Experiences in South Korea

Hyrewon Bae

Department of Social Services Policy Research, Korea Institute for Health and Social Affairs, Sejong City, South Korea

Introduction: Despite rising multiple birth rates in South Korea due to delayed motherhood and assisted reproductive technologies, research on the lived caregiving experiences of families remains limited. Most existing studies focus on birth statistics or neonatal outcomes, overlooking the distinct physical, emotional, and practical demands of raising multiples. This study investigates the lived experiences of women who have given birth to and are raising multiples, addressing this significant research gap. Materials & Methods: This study employed Charmaz’s constructivist grounded theory to explore lived experiences of women raising multiples. In-depth interviews were conducted with 24 mothers who conceived multiples through medically assisted reproduction and were raising twins or higher order multiples aged 12−24 months. Participants were recruited using purposive and theoretical sampling via online parenting communities. Data collection and analysis were carried out concurrently using ATLAS.ti 25 following initial, focused, and theoretical coding procedures. Results: Analysis revealed 18 major categories describing complex caregiving experiences. Key findings include ‘Being a mother yet unable to be one’, reflecting paradoxical maternal identity; ‘Everything is my fault, I am guilty to everyone’, indicating pervasive guilt; ‘Mechanized caregiving’ and ‘Home turned into a workplace’, showing transformation of nurturing into survival-oriented tasks; ‘A mother precariously standing at the edge’, ‘Disconnection from social relationships’, ‘Explosions of extreme emotions’, and ‘Struggling to survive,’ revealing profound physical, emotional, and social burdens. Conclusions: Findings reveal that caring for multiples represents a qualitatively different parenting experience requiring specialized support systems. Results indicate the need for enhanced healthcare and social services tailored to multiple birth families, suggesting targeted interventions that complement existing maternal-child health programs. This research contributes to understanding multiple birth families’ unique needs and informs policy development for more comprehensive support systems, ultimately benefiting multiple birth communities through evidence-based insights that can guide the development of appropriate resources and recognition of their distinct caregiving challenges.

Radiomics and Its Application in Twin Research

David Laszlo Tarnoki^1,2 and Adam Domonkos Tarnoki^1,2

¹Oncologic Imaging and Invasive Diagnostic Centre and the National Tumor Biology Laboratory, National Institute of Oncology, Budapest, Hungary, ²Medical Imaging Centre, Semmelweis University, Budapest, Hungary

Introduction: In recent years, radiomics — the high-throughput extraction of quantitative features from medical images — has gained significant traction, especially through integration with artificial intelligence (AI) technologies. In radiology, AI-driven tools are revolutionizing oncologic screening by enhancing diagnostic accuracy, reducing human error, and accelerating interpretation workflows. This is particularly relevant in early cancer detection via modalities such as mammography and low-dose chest CT. Materials & Methods: Current research at the National Institute of Oncology in Hungary demonstrates the potential of machine learning and deep learning techniques in identifying imaging biomarkers linked to tumor biology, prognosis, and therapeutic response. Notably, AI algorithms can uncover subtle imaging patterns imperceptible to the human eye, paving the way for precision medicine. Results: While radiomics has predominantly focused on cancer diagnostics, its application in twin research opens new avenues for exploring genetic and environmental influences on disease phenotypes. By comparing radiomic profiles across monozygotic and dizygotic twins, researchers can disentangle hereditary factors from lifestyle-related variations in imaging phenotypes. This approach holds promise for identifying novel imaging biomarkers that are both biologically meaningful and clinically relevant. Conclusions: The integration of radiomics in twin studies, combined with advances in AI, represents a transformative shift in biomedical imaging. This synergy has the potential to not only refine diagnostic and prognostic tools in oncology but also enhance our understanding of complex genetic-environmental interactions in health and disease.

Investigating the Relationship Between Intrauterine Inflammation and DNA Methylation at Birth Using Twin Models

A. Hanif¹, Y.T. Wong^1,2, T. Silk^1,2 and J. M. Craig^1,2,

¹School of Medicine, Deakin University, Geelong, VIC, Australia, ²Murdoch Children’s Research Institute, Melbourne, VIC, Australia

Introduction: Prenatal inflammation in the placenta, cords and amniotic fluid is associated with impaired neurodevelopment and motor development, potentially mediated by epigenetic and genetic factors. No study has investigated the association between prenatal inflammation and DNA methylation at birth using monozygotic and dizygotic twins. To address this gap, the study analysed DNA methylation array data from same-sex twins at birth to identify inflammation-associated CpG sites hypothesised to be enriched in inflammatory pathways. Materials & Methods: Cord blood C-reactive protein was used as a surrogate for prenatal inflammation, and DNA methylation was generated from buccal swabs from 242 twin pairs in the Peri/post-natal Epigenetic Twin Study (PETS) cohort using Illumina MethylationEPIC arrays. Within- and between-pair twin regression models, adjusted for shared (sex, zygosity, chorionicity) and non-shared (birth weight for gestational age, cell-type heterogeneity) factors, were used to identify CpG sites and regions strongly associated with prenatal inflammation. Models were fully controlled for genetics in monozygotic pairs and partially in dizygotic pairs. Pathway enrichment analysis was conducted on genes annotated to CpG sites significantly associated with prenatal inflammation (FDR < 0.05). Results: Prenatal inflammation was positively skewed, consistent with prior studies. Quality control of DNA methylation data identified and corrected mislabelled samples using control SNP probes. Batch effects and cell-type heterogeneity correlated with major principal components were addressed through batch correction and model adjustment. Regression results will be presented. Conclusions: Results may reveal critical epigenetic pathways linked to prenatal inflammation, offering insights into the aetiology and potential management of later developmental disorders.

Multi-Gene Mitochondrial Sequencing Reveals Somatic Discordance in Monozygotic Twins: A Forensic Perspective

Kopal Kapoor and Malay A. Shukla

School of Forensic Sciences, National Forensic Sciences University, Gandhinagar, India

Introduction: Monozygotic twins (MZT) assumed to be genetically and phenotypically identical, diverge as a result of series of postzygotic events. The early embryonic somatic mutations make them distinct and discordant for multiple traits like disease susceptibility, growth, and behavior. In forensic context, identification of MZT is crucial as STR profiling is ineffective in identifying genetic differences. Next Generation Sequencing (NGS) enables to differentiate between MZT using postzygotic de novo polymorphisms. Materials & Methods: A total of 50 same-sex twin pairs samples collected from across India were subjected for Zygosity assessment using the GlobalFiler™ Amplification Express Kit, after which 17 MZT pairs were subjected to Sanger sequencing using a multi-gene approach. The mitochondrial D-loop (1150 bp) and cytochrome oxidase I (COI) region (650 bp) were amplified and sequenced, and resultant data were aligned followed by variant detection using MITOMAP software. Results: The mtDNA analysis of 34 samples (17 pairs) revealed a total of 110 variations compared to revised Cambridge Reference Sequence (rCRS). The presence of several known variants documented for various populations confirms the absence of false positives. However, comprehensive NGS validation is required to investigate its genomewide SNP discovery, superior sensitivity, deep coverage, and cost-efficiency compared to single-locus Sanger sequencing. Conclusion: While NGS identifies genetic variants with greater confidence as compared to Sanger sequencing, the latter may be utilized for initial sequence analysis due to its cost-effectiveness. By employing a multi-gene approach, Sanger sequencing enables the detection of variants accurately and potentially provide direction for NGS pipelines, thereby simplifying and reducing the cost of MZT differentiation.

Using Twin Data to Examine Heritable and Intrauterine Hormonal Influences on Transgender and Gender Diverse Identities

A. Ravine^1,2, W. Conabere^1,2, S. Malta^3,4, L. Bourchier³, F. Harte^5,6, J. L. Hopper^4,7 and K. C. Pang^1,2,8

¹Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia, ²Clinical Sciences, Murdoch Children’s Research Institute, Melbourne, VIC, Australia, ³Sexual Health Unit, University of Melbourne, Melbourne, VIC, Australia, ⁴Twins Research Australia, University of Melbourne, Melbourne, VIC, Australia, ⁵Department of Psychiatry, University of Melbourne, Melbourne, VIC, Australia, ⁶Ramsay Clinic Albert Road, Melbourne, VIC, Australia, ⁷Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, VIC, Australia, ⁸Department of Adolescent Medicine, The Royal Children’s Hospital Melbourne, Melbourne, VIC, Australia

Introduction: Previous twin study reports have suggested genetic and prenatal hormonal contributions to gender diversity, albeit using small datasets. Materials & Methods: To further examine this issue, we recruited 27 twin pairs from two Australian specialist gender clinics and obtained details of zygosity and self-reported gender identity. To increase the power of our analysis, we pooled our observations with previously published twin data comprising 436 twins that used comparable methods to our own. Results: The pooled sample of 463 twin pairs included 47/222 (21.2%) monozygotic (MZ) and 21/241 (8.7%) dizygotic (DZ) concordant pairs. Based on a 1% population prevalence estimate, the estimated relative risk ratios for transgender concordance were 21.2 for MZ pairs (95% CI [16.4, 27.3]), and 8.7 for DZ pairs (95% CI [5.8, 13.1]). Conclusions: These findings suggest a substantial genetic contribution to gender diversity. In contrast, the combined results for concordance among same and opposite sex DZ pairs were 12/131 (9.2%) and 9/110 (8.2%) respectively and did not support a role for a prevailing contemporary view that prenatal sex hormone exposure among opposite-sex DZ twin pairs contributes to the occurrence of gender diversity.

Brain White Matter and Gut Microbiota Biomarkers in Multiple Sclerosis: A Pilot Neuroimaging Twin Study

Amirmasoud Alijanpourotaghsara¹, Amirreza Alijanpourotaghsara¹, Arsalan Vessal¹, Seyed Sina Banihashemi¹, Beatrix Beszedics¹, Marton Piroska¹, Aliz Persely^1,2, Helga Szabó^1,3, János Juhász^4,5, Nora Makra⁴, Dora Szabo⁴, David Laszlo Tarnoki¹ and Adam Domonkos Tarnoki¹

¹Medical Imaging Centre, Semmelweis University, Budapest, Hungary, ²Neurology Department, Medical Centre Hungarian Defence Forces, Budapest, Hungary, ³Central Radiological Diagnostic Department, Medical Centre Hungarian Defence Forces Budapest, ⁴Institute of Medical Microbiology, Semmelweis University, Budapest, Hungary, ⁵Faculty of Information Technology and Bionics, Pazmany Peter Catholic University, Budapest, Hungary

Introduction: In multiple sclerosis (MS), distinguishing disease-driven brain changes from inherited risk remains a major challenge. Monozygotic (MZ) twins discordant for MS offer a rare framework to isolate disease-specific alterations by controlling for genetic background. This study combines neuroimaging and microbiome profiling to identify differences in white matter volume, lesion burden, structural disconnection, and gut microbial composition associated with MS. Materials & Methods: Six twin pairs were recruited, including five monozygotic (MZ) pairs discordant for MS and one concordant pair. One dizygotic and the concordant MZ pair were excluded, yielding four MZ pairs for analysis. Brain MRI was used to assess white matter volume, lesion burden, and tract-level disconnection. Within-pair comparisons were conducted using paired t-tests or permutation testing. In three pairs, stool samples underwent 16S rRNA sequencing to evaluate gut microbiota composition. Results: MS-affected twins showed lower white matter volume (−16.6 cm³, p = .013) and a trend toward greater abnormal-appearing white matter (+0.47%, p = .054). Lesion count and volume were higher in affected twins (count: +15.25, volume: + 6.57 cm³; p ≈ .05). Disconnection probability in the left corticospinal tract was increased (+52.7%, p = .039). Microbiota analysis revealed reduced Sutterella abundance in MS twins, consistent with prior studies; other microbial shifts were exploratory. Conclusion: This pilot study demonstrates that white matter volume loss, lesion burden, and tract disconnection in MS can occur independently of genetic background, supporting their role as disease-driven changes. Preliminary microbiota findings, including reduced Sutterella, suggest potential gut–brain interactions in MS pathogenesis.

Gut Microbiome in Twins Affected by Breast Cancer

Adam Domonkos Tarnoki^1,2, Fruzsina Martinovszky², Szilard Veres¹, Beatrix Beszedics^1,2, Mark Di Giovanni³, Bettina Budai², Istvan Szabo¹, Janos Juhasz^4,5, Nora Makra⁴, Dora Szabo⁴, Henriett Butz⁶, Attila Patocs⁶, Bálint Török¹, Mátyás Ujlaki¹ and David Laszlo Tarnoki^1,2

¹Oncologic Imaging and Invasive Diagnostic Centre and the National Tumor Biology Laboratory, National Institute of Oncology, Budapest, Hungary ²Medical Imaging Centre, Semmelweis University, Budapest, Hungary, ³Doctoral School, Semmelweis University, Budapest, ⁴Institute of Medical Microbiology, Semmelweis University, Budapest, Hungary, ⁵Faculty of Information Technology and Bionics, Pazmany Peter Catholic University, Budapest, Hungary, ⁶Molecular Genetic Department and the National Tumor Biology Laboratory, National Institute of Oncology, Budapest, Hungary

Introduction: Breast density is a known risk factor for breast cancer and is influenced by both genetic and environmental factors. Emerging evidence suggests the gut microbiome may contribute to cancer development through metabolic and immune pathways. This study aimed to explore the relationship between gut microbiome composition and breast cancer. Materials & Methods: Twenty-eight twins (11 monozygotic, 3 dizygotic pairs; average age 54.2 ± 14.3 years) from the Hungarian Twin Registry participated. At least one twin in each pair had a history of breast cancer, including two with active disease. Participants underwent breast imaging (mammography and ultrasound), genetic testing for cancer predisposition, blood sampling (for DNA and epigenetics), lifestyle questionnaires, and provided stool samples for microbiome analysis. Results: At the phylum level, Actinobacteria were more abundant in tumor-affected twins, while Proteobacteria were consistently more prevalent in non-tumor individuals. Members of the order Rhodospirillales appeared more often in non-tumor twins of discordant pairs. The genus Bifidobacterium was more abundant in tumor-affected individuals, whereas Agathobacter was typically higher in non-tumor samples, though this varied across pairs. No significant differences were found between individuals with and without hereditary predisposition. Microbiomes of concordant twin pairs were not more similar than those of discordant pairs. Conclusions: Our findings support a link between gut microbiome composition and breast cancer, particularly the roles of Proteobacteria and Bifidobacterium. These differences may influence breast tissue characteristics like density, suggesting a potential role for microbiome profiling in risk assessment and personalized prevention.

Causal Associations Between Cardiometabolic Risk Factors and Anxiety and Depression in Sri Lanka

F. A. Brenes-Castillo^1,2, M. Herle³, A. Sumathipala⁴, F. V. Rijsdijk ⁵, L. Dissanayake ⁴, K. Jayaweera⁴, S. Jabir ⁴ and H. M. S. Zavos¹

¹Department of Psychology, Institute of Psychiatry, Psychology & Neuroscience, Kings College London, London, UK, ²National Institute for Health and Care Research (NIHR) Maudsley Biomedical Research Centre (BRC), London, UK, ³Social, Genetic & Developmental Psychiatry Centre, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK, ³Department of Psychology, Institute of Psychiatry, Psychology & Neuroscience, Kings College London, London, UK, ⁴Institute for Research and Development in Health and Social Care, Sri Lanka, ⁵Anton de Kom Universiteit van Suriname (ADeKUS), Paramaribo, Suriname

Introduction: Cardiovascular disease is one of the leading causes of mortality in Sri Lanka. People with cardiovascular disease often experience anxiety and depression symptoms, reduced quality of life, and worse prognosis. However, no previous study has explored whether there are causal associations between cardiometabolic risk factors and anxiety and depression in a Sri Lankan twin cohort. This study aims to apply a direction of causation twin model to assess causal associations between two latent factors, cardiometabolic risk factors and mental health in the Colombo Twin and Singleton Study (COTASS) dataset. Materials & Methods: We will conduct a secondary data analysis with the COTASS dataset. We will use data from the second wave 2012−2015 (2934 twins and 1035 singletons) since participants were interviewed about their cardiovascular and mental health. We will apply a direction of causation twin model to assess causal associations between two latent factors, cardiometabolic risk factors (fasting blood glucose; blood pressure; fasting blood insulin; HDL cholesterol; triglyceride; and waist circumference) and mental health (i.e., anxiety and depression). The direction of causation analysis will look at patterns of cross-twin and cross-trait correlations. Results: This research is ongoing. Based on previous research, we expect to find a bidirectional causal association between cardiometabolic risk factors and anxiety and depression. Conclusions: This genetically informed study will help improve the representativeness and diversity of twin studies, determine whether causal relationships between cardiometabolic risk factors and mental health are bidirectional, and provide guidance to inform public healthcare strategies at local levels.

Birth DNA Methylation and Full-Scale IQ at Age 11: Insights From a Twin-Based Epigenome-Wide Analysis

Rashadul Islam¹, Yen Ting Wong¹, Tim J. Silk^2,3 and Jeffrey M. Craig ^1,3

¹The Institute for Mental and Physical Health and Clinical Translation (IMPACT) and School of Medicine, Deakin University, Waurn Ponds, VIC, Australia, ²Centre for Social and Early Emotional Development (SEED) and School of Psychology, Deakin University, Melbourne, VIC, Australia, ³Murdoch Children’s Research Institute, Melbourne, VIC, Australia

Introduction: Epigenetic variation at birth may influence later cognitive development, but the extent to which birth DNA methylation relates to intellectual outcomes remains unclear. Most prior studies have not adequately addressed shared genetic and environmental influences. This study examines associations between DNA methylation at birth and Full-Scale IQ (FSIQ) at age 11 using a twin design. Materials & Methods: We analyzed 59 same-sex twin pairs from the Peri/post-natal Epigenetic Twin Study (PETS). DNA methylation was measured in buccal swabs collected at birth using the Illumina MethylationEPIC array. After quality control, preprocessing and normalization, approximately 690,000 CpG sites were retained. Two complementary models were used: (1) a decomposition model separating within- and between-pair effects, and (2) a within-pair difference model that captures associations based on methylation and IQ differences between co-twins. Models included covariates such as sex, zygosity, birthweight-for-gestational-age, BMI, batch, and epithelial cell composition. The top 1000 CpG sites from each model will be used for gene annotation and pathway analysis. Results: Analysis is ongoing. Initial results aim to identify methylation sites at birth that are consistently related to cognitive scores across both models. Enrichment analyses will explore biological processes involved in neurodevelopment and cognitive function. Conclusions: This study uses a twin-based design to isolate early-life epigenetic variation linked to later cognitive performance. Findings will provide insight into mechanisms influencing cognitive development and inform early identification strategies relevant to twins, multiples, and broader child health research.

Dissecting Arterial Stiffness and Lifestyle Contributions to White Matter Hyperintensity Burden: An Exploratory Twin Study

Amirreza Alijanpourotaghsara¹, Amirmasoud Alijanpourotaghsara¹, Arsalan Vessal¹, Seyed Sina Banihashemi¹, Beatrix Beszedics¹, Marton Piroska¹, Aliz Persely^1,2, Helga Szabó^1,3, János Juhász^4,5, Nora Makra⁴, Dora Szabo⁴, David Laszlo Tarnoki¹ and Adam Domonkos Tarnoki¹

¹Medical Imaging Centre, Semmelweis University, Budapest, Hungary, ²Neurology Department, Medical Centre Hungarian Defence Forces, Budapest, Hungary, ³Central Radiological Diagnostic Department, Medical Centre Hungarian Defence Forces Budapest, Hungary, ⁴Institute of Medical Microbiology, Semmelweis University, Budapest, Hungary, ⁵Faculty of Information Technology and Bionics, Pazmany Peter Catholic University, Budapest, Hungary

Introduction: White matter hyperintensities (WMH) are prevalent in aging brains and are linked to increased risk of stroke and dementia. While genetic factors contribute to WMH, the role of arterial stiffness and lifestyle factors remains incompletely understood. Monozygotic twin studies allow control for genetic background, providing a unique opportunity to explore environmental and vascular influences on WMH burden. Methods: We studied 29 monozygotic twin pairs with MRI WMH volumes, carotid Intima-Media Thickness (IMT), aortic Pulse Wave Velocity (PWV), lifestyle data and cognitive scores. Absolute differences within twin pairs defined discordance status, split at the median total WMH volume difference (0.51 cm³). Mann–Whitney U tests compared discordant and concordant groups on vascular, lifestyle, and cognitive measures. Correlation analyses evaluated relationships between vascular measures and WMH burden. Results: Discordant twin pairs exhibited significantly greater differences in aortic PWV (median 2.0 m/s vs. 1.2 m/s, p = .03), highlighting arterial stiffness as a key contributor to WMH burden discordance. While differences in lifestyle scores, carotid IMT, and MOCA scores were observed between groups, these did not reach statistical significance. Correlation analysis showed a modest inverse relationship between PWV differences and WMH volume differences (r = –.27, p = .11), further supporting vascular stiffness as a potential mechanistic factor. Conclusion: Our findings demonstrate that arterial stiffness, measured by PWV, is significantly associated with WMH burden differences in genetically identical twins, underscoring the importance of vascular health beyond genetics in cerebral small vessel disease. Although lifestyle factors showed trends towards association, larger studies are needed for confirmation. Targeting vascular stiffness may represent a modifiable strategy to slow WMH progression and cognitive decline.

Addressing Patient-Provider Communication Gaps in Vanishing Twin Syndrome: Implications for Patient Care and Clinical Guidelines

N. Cubbage¹, S. L. P. Schilit², A. Groff³, S. Ernst⁴ and M. Nascarella¹

¹Department of Public Health, Behavioral and Health Sciences, Massachusetts College of Pharmacy and Health Sciences, Boston, MA, USA, ²Myriad Genetic Laboratories, Inc., USA, ³Capital Women’s Care, USA, ⁴TAPS Foundation, the Netherlands

Introduction: Vanishing twin syndrome (VTS) refers to the in-utero demise of one or more fetuses in a multiple pregnancy, often with physical remains persisting throughout gestation or at birth. Despite increased detection via early ultrasound and the use of assisted reproductive technologies (ART, clinical protocols for VTS remain inadequate. This systematic review assessed physical and psychological risks, patient-provider communication, and international guideline gaps in VTS care. Materials & Methods: A systematic literature review was conducted using key search terms including but not limited to ‘vanishing twin* syndrome’, ‘patient-provider communicat*’, and ‘bereave* care’. Studies were selected based on relevance to patient experiences, international clinical guidelines, and the physical and psychological impacts of vanishing twin syndrome. Results: Patients with VTS report inconsistent disclosure, inadequate emotional support, and confusion regarding the management of fetal remains. Physical risks to surviving multiples include low birth weight, placental pathology, and neurodevelopmental concerns. Maternal serum screening and cfDNA results are often confounded due to lingering fetal DNA or hormones from the demised fetus. These complications are underreported and poorly explained in current research and clinical guidance. Conclusions: Improved VTS management requires early chorionicity assessment, updated screening protocols, and training on compassionate disclosure. Evidence-based guidelines should account for screening artifacts, placental sequelae, and bereavement care. Future studies must stratify outcomes by gestational age at loss, chorionicity, and ART exposure to clarify risks and optimize care.

Mental Health Problems in Mothers of Twins

Yoon-Mi Hur and Suk Kyung Nam

Kookmin Twin Research Institute, Kookmin University, Seoul, South Korea

Introduction: The rate of twin births has increased markedly in recent decades in South Korea and other developed countries, largely due to the widespread use of assisted reproductive technology (ART). Given the heightened demands associated with raising two children simultaneously and the common experience of subfertility among mothers of twins, these mothers may be at increased risk for mental health problems. Materials & Methods: An online survey was conducted using the General Health Questionnaire (GHQ) along with a demographic questionnaire. Participants included 780 South Korean mothers of twins and 912 mothers with at least two singleton children. After controlling for maternal age, education, and number of children, mental health outcomes were compared between mothers of singletons and mothers of twins. Results: In both groups — mothers of singletons and mothers of twins — those who conceived via ART reported significantly higher levels of mental health problems compared to those who conceived spontaneously. Furthermore, mothers of twins exhibited significantly higher levels of mental health problems than mothers of singletons. Among mothers who conceived spontaneously, those with dizygotic twins reported more mental health problems than those with monozygotic twins; this difference was not observed in the ART group. Conclusions: These findings have implications for the interpretation of classical twin studies on mental health. Moreover, they highlight the need for targeted intervention and prevention strategies to support the mental health of mothers of twins.

Hungarian Twin Study on COVID-19 Vaccination Status

G. Szabó^1,2, Á. D. Tárnoki^2,3, M. Piroska³, M. D. Giovanni¹ and D. L. Tárnoki^2,3

¹Doctoral School, Semmelweis University, Budapest, Hungary, ²Oncologic Imaging and Invasive Diagnostic Centre and the National Tumor Biology Laboratory, National Institute of Oncology, Budapest, Hungary, ³Medical Imaging Centre, Semmelweis University, Budapest, Hungary

Introduction: The SARS-CoV-2 pandemic has had profound global health, economic, and social impacts, with over 770 million confirmed cases and more than 7 million deaths reported to WHO. Although several effective vaccines have been developed, public willingness to get vaccinated has varied substantially across regions and demographic groups, influenced by trust, access, misinformation, and perceived risks. Understanding the determinants of vaccination behavior — including genetic and environmental contributions — can guide targeted public health interventions. Our study aimed to identify factors influencing vaccine uptake and assess familial and genetic effects on vaccination status in Hungary. Materials & Methods: We conducted a questionnaire-based online survey among members of the Hungarian Twin Registry from July 2022 to April 2023, following the fifth wave of the COVID-19 pandemic, to assess vaccination status and attitudes. Results: A total of 813 twins responded (74.7% women; 460 monozygotic [MZ], 353 dizygotic [DZ]; age range 19–84 years). Discordant vaccination status was found in 19/160 (11.9%) MZ and 14/95 (14.8%) DZ pairs. Vaccination status was significantly influenced by the co-twin’s status (p < .001), while zygosity had no significant effect (p = .61; p = .13 when adjusted for gender in DZ pairs). Reasons for nonvaccination were not more similar among unvaccinated twin pairs than in the general population (p = .96). Conclusions: Co-twin influence plays a significant role in COVID-19 vaccination decisions, whereas genetic similarity does not, suggesting shared familial and environmental factors are more important than genetic predisposition in vaccine uptake.

Analysis of Twin Pregnancy Trends and Maternal and Infant Complications From 2015 to 2024: A Single-Center Retrospective Cohort Study

Yangyang Li, Shaowei Yin, Chuang Li, Jun Wei and Caixia Liu

Department of Obstetrics & Gynecology, Shengjing Hospital of China Medical University, Shenyang, China

Introduction: With the development of ART, the incidence of twin pregnancy has increased, and the number of older parturients has increased. Precise health care during twin pregnancy is particularly important. Materials & Methods: Parturients and their perinatal infants who were hospitalized in Shengjing Hospital from 2015 to 2024 and delivered at gestational age ≥ 28 weeks were selected as study subjects. The change trend of twin pregnancy incidence, maternal characteristics and differences of maternal complications were retrospectively analyzed. Results: From 2015 to 2024, the delivery rate of twin pregnancy decreased from 4.16% to 3.01%, showing an overall downward trend (χ² trend = 61.06, p < .001), and the incidence rate of age ≥ 32 years old showed an upward trend (χ² trend = 15.73, p < .001), the incidence of IVF-ET showed an upward trend (χ² trend = 46.94, p < .001). The incidence of GDM showed an increasing trend (p < .05). The incidence of premature labor and late premature labor showed a decreasing trend (p < .001). Compared with 2015−2019, the incidence of age ≥ 32 years old, IVF-ET, and GDM increased significantly in 2020−2024 (p < .05), while the incidence of preterm birth and late preterm birth decreased significantly (p < .05). Conclusions: The proportion of pregnant women ≥32 years old in twin pregnancy increases, and the incidence of maternal complications increases. Accurate pregnancy management and health care of twin pregnancy are particularly important.

Perinatal Outcomes of Monochorionic Monoamniotic Twin Pregnancies Followed Up in a Single Tertiary Level Centre

S. Roero¹, S. Arduino¹, A. Ingala¹, C. Peila², C. Bossotti¹, I. Ferrando¹, M. Folino Gallo¹, A. Aiello¹, M.F. Greco¹, A. Coscia² and A. Revelli¹

¹Gynaecology and Obstetrics 2U, Sant’Anna Hospital, Azienda Ospedaliero Universitaria Città della Salute e della Scienza di Torino, University of Turin, Turin, Italy, ²Department of Public Health and Pediatrics, A.O.U. Città della Salute e della Scienza, University of Turin, Turin, Italy

Introduction: Monochorionic monoamniotic (MCMA) pregnancy is the rarest type of twin pregnancy, with very high risk of fetal loss. The aim of the present work is to describe perinatal outcomes and risk of early- and late-pregnancy fetal loss of a cohort of MCMA twin pregnancies followed up in a single center over a 20-year period and to identify which obstetric variables mostly influence the incidence of neonatal adverse outcome. Materials & Methods: Retrospective cohort study including MCMA twin pregnancies followed up at the Twin Pregnancy Care Unit of Sant’Anna Hospital in Turin (Italy) between 2005 and 2024. Chorionicity and amnionicity were diagnosed in the first trimester. Results: A total number of 53 MCMA twin pregnancies have been included in the study, of which 42 progressed beyond 24 weeks of gestation. The rate of fetal loss before 24 weeks of GA was 19.8%, while that of intrauterine fetal demise after 24 weeks resulted 3.6%; the incidence of overall intrauterine losses was 23.6%; 80.5% of liveborn twins were female. Around one fourth of the newborn babies (26.8%) had an adverse outcome, which was significantly influenced by gestational age at birth, birthweight and presence of malformations. The incidence of congenital malformations in our sample was 13.4%. Conclusions: Most fetal losses occur before 24 weeks of gestation and the rate of fetal demise after this cutoff is quite low. It could be worth postponing elective delivery to 34 weeks of gestational age or beyond, to reduce perinatal complications associated with premature birth.

Intrahepatic Cholestasis in Twin Pregnancy

S. Roero, S. Arduino, A. Ingala, C. Bossotti, I. Ferrando, M. Folino Gallo, A. Aiello, M. F. Greco and A. Revelli

Gynaecology and Obstetrics 2U, Sant’Anna Hospital, Azienda Ospedaliero Universitaria Città della Salute e della Scienza di Torino, University of Turin, Turin, Italy

Introduction: Intrahepatic cholestasis (ICP) is the most common liver disease in pregnancy, and it is associated to maternal as well as fetal-neonatal complications. Incidence of ICP is reported to be higher in twin gestations compared to singletons. The aim of the present study is to describe perinatal outcomes of twin pregnancies with ICP by comparing them to twin pregnancies without ICP. Materials & Methods: A retrospective cohort study including twin pregnancies followed up at the Twin Pregnancy Care Unit of Sant’Anna Hospital in Turin (Italy) between January 2016 and December 2024. Twin pregnancies complicated by ICP formed the case group, while those without ICP formed the control group. ICP was defined by the presence of pruritus associated to non-fasting total serum bile acids (TSBA) ≥ 19 µmol/L. Results: A total of 712 twin pregnancies were included in the study, of which 40 were complicated by ICP and 672 were not. Women presenting with ICP were significantly older (37.4 vs. 33.4 years, p < .001) and more often nulliparous (80.0% vs. 54.8%, p < .002); also, they were more likely to have conceived via assisted reproduction (42.5% vs. 21.8%, p < .002). Twin pregnancies complicated by ICP had a higher incidence of both reduced cervical length (40.0% vs. 22.0%, p < .009) and hypertensive disorders or pregnancy (15.0% vs. 8.2%, p < .043). Conclusions: ICP in twin pregnancy is associated with a higher risk of threatened preterm labour and hypertensive disorders of pregnancy. Close monitoring of twin pregnancies with this complication is needed to improve maternal and fetal outcomes.

Adult Twin Relationship Quality and Aggression: An Experimental Study

B. Dinić¹, M. Oljača¹, Ž. Nikolašević² and S. Smederevac¹

¹Department of Psychology, Faculty of Philosophy, University of Novi Sad, Serbia, ²Department of Psychology, Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia

Introduction: Previous research on twin relationship quality has mainly focused on children and adolescents, while little is known about adult twin dynamics. This experimental study extends previous work on adult twinship by examining several aspects of twin relationships — such as warmth and aggression — through the lens of their genetic and environmental underpinnings, as well as the effects of zygosity and sex constellation on these relational outcomes. Materials & Methods: On a sample comprised 336 twins (75.3% females, average age was 24.21, all White) from Serbian Twin Registry, the Adult Sibling Relationship Questionnaire (with dimensions of warmth, conflict, and rivalry) was used and the Competitive Reaction Time Task for inducting aggression toward twin pair. Zygosity was determined by DNA analysis of buccal swabs. Results: Results showed that dimensions of twin relationship quality and aggression toward a twin pair can be explained based only on environmental factors, with higher contributions shown by specific both shared and non-shared environmental factors (0.3−0.56) compared to common ones (0.01−0.28). Furthermore, monozygotic twins exhibited higher warmth towards each other (ηp² = .05), while sex constellation showed no significant effects on twin relationship quality aspects. Among the zygosity, sex constellation, and dimensions of twin relationship quality, only conflict showed a significant and positive effect on aggression toward twin pair (ηp² = .02). Conclusions: The results revealed that conflict is the primary factor contributing to aggression toward a twin pair, while zygosity is the key factor influencing the positive aspects of twin relationship quality. These findings underscore the distinct mechanisms underlying closeness and conflict in adult twinship and pointing to the need for targeted, environment-focused interventions to support healthier sibling dynamics in adulthood.

The Role of Multiple Birth Organizations in Research

C. E. Lister

International Council of Multiple Birth Organisations

One of the objectives of the International Council of Multiple Birth Organisations (ICOMBO) is to ‘Conduct and participate in ethical research projects for the benefit of multiples and their families and disseminate their findings’. Multiple birth organizations (MBOs) can play a key role in research projects from inception to conclusion. Collaboration between researchers and MBOs can help make meaningful differences for multiple birth families. Understanding the views of multiples and their families is a critical consideration to make sure the rights and needs of study participants are considered. A 2018 ICOMBO study provided insights into the willingness of multiples and their families to participate in research. This included how the study aligned with their values and what was required of the participants (e.g., simple measures vs. taking biological samples). ICOMBO has assisted with research grant applications by providing letters of support vouching for the importance of studies to our member families and how we can contribute. MBOs also play a key role in assisting with recruitment for studies. Finally, ICOMBO provides a way to communicate the findings of studies to the multiples community and has provided multiple birth family perspectives in research papers. Lay summaries of recent research studies are written for our quarterly newsletters and summaries of research projects are also available on our website. In conclusion, MBOs have an important role to play in contributing to research projects. We want to encourage more partnerships between twin researchers ICOMBO/MBOs worldwide, for the benefit of both parties.

The Experiences of Patients With Vanishing Twin Syndrome: A Mixed-Methods Exploration of Patient Satisfaction and Miscarriage Information

Nichole M. Cubbage¹, Nicholas Embleton² and Carly Levy¹

¹Department of Public Health, Behavioral and Health Sciences, Massachusetts College of Pharmacy and Health Sciences, Boston, MA, USA, ²Newcastle University and Newcastle Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK

Introduction: Vanishing twin syndrome is a miscarriage of multiples where one or more fetuses ‘vanishes’ (i.e., partial or full resorption or via calcification) during pregnancy, often before detection via ultrasound. It affects 30−50% of multifetal pregnancies, with most cases resulting in full resorption within the first trimester. Despite its recognition since 1945 and rising occurrence in both natural and assisted pregnancies, standardized clinical guidelines remain inadequate, leading to inconsistent diagnosis, counseling, and communication from healthcare providers. This study examines the experiences of mothers and gestational carriers diagnosed with VTS, focusing on patient-provider communication, risks, and symptom disclosure. Materials & Methods: A global online survey collected qualitative and quantitative data from 153 participants across 17 countries. Results: Results show that most patients with formal diagnoses experienced negative interactions with healthcare providers, with an average sentiment score of −0.7 (on a scale from −2 to 2). Over 53.4% rated their communication experience as −1, and the average satisfaction score for the amount of information received was 3.5/10. Additionally, 43% of respondents were not informed about chorionicity, a key factor affecting fetal outcomes. Significant discrepancies in care were observed across different countries. Conclusion: The findings highlight major gaps in patient-provider communication and inconsistent clinical practices regarding VTS. Addressing these issues through improved education, clearer protocols, and standardized guidelines could enhance patient experiences and decision-making. Future research should focus on provider training and evidence-based strategies to improve the management of VTS and other types of miscarriage and death of multiples during pregnancy and postpartum.