Africa represents a uniquely important context for twin research, given its consistently high rates of dizygotic (DZ) twinning, rapid demographic growth, and exceptional genetic, cultural, and environmental diversity (Monden et al., Reference Monden, Pison and Smits2021; Ouedraogo et al., Reference Ouedraogo, Pison, le Coeur and Soura2025; Pison et al., Reference Pison, Monden and Smits2015; Smits & Monden, Reference Smits and Monden2011). Across human populations, twinning rates vary markedly by geography, with the highest natural rates observed in sub-Saharan Africa and the lowest in East and Southeast Asia. Africa has the highest twinning rates globally, particularly within a recognized ‘twin belt’ stretching across West and Central Africa. Countries such as Benin, Nigeria, Côte d’Ivoire, the Central African Republic, and the Democratic Republic of the Congo record some of the highest twin birth rates in the world, often exceeding 20 twin deliveries per 1000 births (Figure 1), compared with approximately 6–9 per 1000 in many Asian populations and intermediate rates in Europe and the Americas (Monden et al., Reference Monden, Pison and Smits2021; Smits & Monden, Reference Smits and Monden2011). This pattern is largely driven by elevated DZ twinning, whereas monozygotic (MZ) twinning rates appear relatively stable worldwide (REF).
Average twinning rates in Africa and countries with twin registries participating in the African Twin Registry (AfTR). Twin deliveries per 1000 total deliveries (Smits & Monden, Reference Smits and Monden2011).
Recent evidence further shows that twinning in Africa has remained high over time, even as patterns elsewhere have changed substantially. In many high-income countries, twin rates rose sharply from the 1980s onward, largely due to delayed childbearing and the widespread introduction of medically assisted reproduction, before stabilizing in recent years (Monden et al., Reference Monden, Pison and Smits2021; Pison et al., Reference Pison, Monden and Smits2015). By contrast, data from 42 sub-Saharan African countries covering 1986–2016 demonstrate persistently elevated twinning rates, with regional variation but no comparable dependence on assisted reproductive technologies (Ouedraogo et al., Reference Ouedraogo, Pison, le Coeur and Soura2025). Comparisons between 1980–1985 and 2010–2015 suggest that while Europe and North America experienced pronounced increases in twin maternities, many African populations maintained already high baseline levels, with moderate increases in some countries reflecting demographic and maternal age changes rather than fertility treatment effects (Monden et al., Reference Monden, Pison and Smits2021; Ouedraogo et al., Reference Ouedraogo, Pison, le Coeur and Soura2025).
Because Africa has also undergone substantial population growth during the same period, the absolute number of twin births has increased markedly. As total births rose across many African countries between the 1980s and 2010s, the number of twins born annually expanded in parallel, resulting in Africa accounting for a growing share of all twin births worldwide (Monden et al., Reference Monden, Pison and Smits2021). Thus, while twinning rates remained comparatively stable and high, twin birth counts increased because of rising fertility and expanding population size. This combination of high natural twinning prevalence and increasing numbers of births makes Africa critically important for future twin-based epidemiological, developmental, and genetic research.
Notably, twins continue to account for a large proportion of neonatal, infant and child mortality in Africa. This is often due to prematurity, low birth weight and other obstetric complications, as well as malnutrition during early life. Previously, it has been estimated that the under-5 years mortality is three times higher among twins than singletons, while for neonates the excess mortality up to five times higher (Christensen & Bjerregaard-Andersen, Reference Christensen and Bjerregaard-Andersen2017). In order to address this, interventions to improve antenatal and emergency obstetric care are needed. This includes identification of twin pregnancies antenatally, where data from Guinea-Bissau show that many twin mothers are unfortunately often unaware of this status (Bjerregaard-Andersen et al., Reference Bjerregaard-Andersen, Lund, Jepsen, Camala, Gomes, Christensen, Christiansen, Jensen, Aaby, Beck-Nielsen, Benn and Sodemann2012). But twins also need additional focus in the months after birth, including home visits to identify malnourished twins failing to thrive (Bjerregaard-Andersen et al., Reference Bjerregaard-Andersen, Biering-Sorensen, Gomes, Bidonga, Jensen, Rodrigues, Christensen, Aaby, Beck-Nielsen, Benn and Sodemann2014).
Recent evidence from Nigerian populations further substantiates the biological and genetic basis of DZ twinning. In a large sample of mothers of DZ twins (N ≈ 1000), strong familial aggregation was observed, with an average of 4 twin pairs among relatives compared to .5 in controls, supporting a substantial genetic contribution (Hur et al., Reference Hur, Martin, Oginni, Boomsma, Hubers and Mbarek2024). Nigeria also exhibits some of the highest twinning rates worldwide (>20 per 1000 births), far exceeding rates observed in other regions. Moreover, mothers of DZ twins display higher parity and earlier age at first birth, reinforcing the link between twinning and female fertility. Together, these findings underscore the scientific importance of African populations for studying reproductive biology and genetic determinants of twinning (Hur et al., Reference Hur, Martin, Oginni, Boomsma, Hubers and Mbarek2024).
Early Steps in African Twin Studies
The obstetrician and epidemiologist Percy Nylander at the University of Ibadan in Nigeria carried out a series of influential twin studies in the 1960s–1980s, with a focus on the extremely high frequency of twins in southwestern Nigeria, especially among the Yoruba population. His work was primarily based at the University of Ibadan and is often considered the first systematic scientific investigation of the ‘Yoruba twinning phenomenon’. Nylander (Reference Nylander1969) showed that south-western Nigeria had the highest recorded twin birth rates in the world, with 45–50 twin maternities per 1000 births in Western Nigeria, a number that is about 3–4 times higher than in Europe or North America. His analyses of large maternity cohorts in Ibadan showed that the excess was almost entirely due to DZ twinning, while MZ rates were similar to those elsewhere. In a comparative study carried out in in Western Nigeria and a Caucasian population in Scotland, it was found that DZ twinning rates varied with maternal age and parity, while the MZ twinning rate remaining constant. A major association in the two populations was maternal serum follicular stimulating hormone (FSH) level (Nylander, Reference Nylander1973). These levels were much higher in the Nigerian than in the Scottish population.
Remarkably, in the Scottish population, twin-prone and nontwin-prone women had similar serum FSH levels, but FSH levels were much higher in twin-prone women in the Nigerian population (Nylander, Reference Nylander1981). This finding is consistent with the most recent findings in the genetic etiology of DZ twinning (Mbarek et al., Reference Mbarek, Gordon, Duffy, Hubers, Mortlock, Beck, Hottenga, Pool, Dolan, Actkins, Gerring, Van Dongen, Ehli, Iacono, Mcgue, Chasman, Gallagher, Schilit, Morton and Martin2024), which identified the FSHB locus as a key genomic region. Nylander (Reference Nylander1979) also suggested that the high incidence might partly reflect dietary exposure to estrogen-like substances. Although these pioneering studies demonstrated Africa’s exceptional value for twin research, they were at the time not followed by continent-wide investment in sustained registries, longitudinal cohorts, or integrated research infrastructure. This gap remains highly visible today.
In parallel with early African studies, broader genetic investigations of human populations provided important insights into the biological basis of twinning, demonstrating substantial variation in DZ twinning rates across populations, with the highest frequencies observed in African populations, intermediate levels in Europeans, and the lowest rates in East Asian populations (Bulmer, Reference Bulmer1970; Morton et al., Reference Morton, Chung and Mi1967). Analyses of interracial populations also provided early evidence that DZ twinning is primarily determined by maternal factors and expressed only in women, with transmission occurring through both maternal and paternal lines but phenotypic expression limited to the mother. Within this framework, White and Wyshak (Reference White and Wyshak1964) and Bulmer (Reference Bulmer1970) later proposed a sex-limited, partially recessive genetic model, with expression occurring in women through increased ovulation. Observations from admixed populations tended to suggest nonadditive genetic effects, as twinning rates in hybrid groups were often lower than expected under a simple additive model of parental-population rates. Together, these findings laid an important conceptual foundation for later molecular genetic studies of twinning and fertility (Mbarek et al., Reference Mbarek, Gordon, Duffy, Hubers, Mortlock, Beck, Hottenga, Pool, Dolan, Actkins, Gerring, Van Dongen, Ehli, Iacono, Mcgue, Chasman, Gallagher, Schilit, Morton and Martin2024).
The Need for Twin Research Infrastructure in Africa
Despite the importance and obvious scientific value of twin data from Africa, the continent remains underrepresented in twin registries, twin research infrastructure, and genomic discovery efforts. In a landmark meta-analysis of heritability estimates based on 2748 twin studies conducted over five decades, only .2% of studies originated from Africa (Polderman et al., Reference Polderman, van Dongen and Boomsma2011). This underrepresentation limits the global generalizability of findings on the genetic and environmental architecture of health, disease, and complex human traits. It also perpetuates broader inequities in human genetics, where African populations remain disproportionately absent from genomic databases and association studies, despite containing the greatest human genetic diversity.
Existing examples demonstrate both feasibility and value. The Nigerian Twin and Sibling Registry was established as a community-based resource enrolling twins and siblings for behavioral genetic and health research (Hur et al., Reference Hur, Kim, Chung, Shin, Jeong and Auta2013). The Guinea-Bissau Twin Registry was developed through the demographic and health surveillance system (HDSS) within the Bandim Health Project (www.bandim.org), with emphasis on survival, growth, metabolic health, and infectious disease outcomes (Bjerregaard-Andersen et al., Reference Bjerregaard-Andersen, Gomes, Joaquím, Rodrigues, Jensen, Christensen, Benn, Aaby, Beck-Nielsen and Sodemann2013). Subsequent work has highlighted continuing opportunities for twin research in Nigeria, particularly in mental health and developmental outcomes (Oginni et al., Reference Oginni, Ayorinde, Ayodele, Opara, Mapayi and Mosaku2024). A recent scoping review further showed that family, twin, and adoption studies of severe mental disorders in sub-Saharan Africa remain limited, underscoring the need for expanded genetically informative research infrastructure across the region (Onu et al., Reference Onu, Olatayo, Okorie and Ohaeri2023). Most other African countries contribute to twin research through cohort studies rather than structured national registries, highlighting a gap between high twinning prevalence and research infrastructure. Together, these initiatives show that twin registries can be successfully established in diverse African settings and can support both classical twin designs and longitudinal public health research.
From a global perspective, strengthening African twin infrastructure could help address longstanding imbalances in twin science. African populations offer opportunities to study diverse ancestries, heterogeneous environments, infectious and noncommunicable disease burdens, fertility patterns, nutrition transitions, and rapid urbanization within genetically informative designs. The establishment of coordinated twin registries with harmonized phenotyping, sustainable follow-up, and secure record linkage systems would therefore benefit not only African public health research, but also international efforts in precision medicine, developmental science, and population health. Addressing the described excess mortality among African twins during early life would also be a key priority here.
African Twins and Multiple Births Research Foundation (ATMBRF) and African Twin Registry (AfTR)
The ATMBRF (https://africantwinsresearch.org), established in 2025, was created to address this gap through coordinated research, advocacy, and infrastructure development. The Foundation aims to advance interdisciplinary research on the biological, clinical, psychological, and sociocultural dimensions of twin and multiple births across Africa. Its mission includes promoting collaborative twin research across African countries, supporting registry development and harmonized data collection, engaging communities and healthcare systems, improving awareness of maternal and child health issues related to multiple births, and building international scientific partnerships.
Central to this mission is the AfTR, a continent-wide initiative designed to systematically identify and follow twins and higher-order multiples across Africa. The ATR is conceived as both a research platform and a public health resource, consistent with best practices in population-based twin registries. Its design emphasizes standardized data collection, longitudinal follow-up, and scalability across diverse national contexts. Currently, while in the establishing phase, the AfTR is receiving inputs from the Nigerian Twin and Sibling Registry (NTSR), and Guinea-Bissau Twin Registry within the Bandim Health Project (BHP).
In Guinea-Bissau, the registry has followed twins within the BHP HDSS since 2009, primarily with the aim of addressing early twin mortality as well as metabolic twin health later in life (Bjerregaard-Andersen et al., Reference Bjerregaard-Andersen, Rodrigues, Benn, Aaby, Christensen and Sodemann2019). As of 2026, a newborn cohort followed since birth includes 46 twins in total, including 21 twin pairs and 4 single twins. A metabolic twin cohort followed since childhood, adolescence and early adulthood counts 372 in total, including 128 twin pairs, 2 triplet sets, and 100 single twins. The cohort is currently between 14 to 46 years old. It is linked to the HDSS using unique ID numbers, enabling the long-term follow-up. Previous genetic analyses among newborn twin pairs in the registry found that approximately 19% are MZ and 81% DZ (Bjerregaard-Andersen et al., Reference Bjerregaard-Andersen, Lund, Jepsen, Camala, Gomes, Christensen, Christiansen, Jensen, Aaby, Beck-Nielsen, Benn and Sodemann2012).
Record Linkage Approaches
A defining feature of the AfTR will be its integration of record linkage methodologies. By linking registry data with civil registration and vital statistics systems, hospital records, and demographic surveillance platforms, the AfTR aims to overcome challenges associated with incomplete or fragmented data systems, ensuring representative groups of participants (e.g., children from hospital records, adults from other sources such as hospital and maternity records, research cohort studies, community-based surveys, national census and survey data, genetic and epidemiological studies) putting into consideration different approaches in different countries.
Operation and Infrastructure
Operationally, the AfTR incorporates both prospective and retrospective recruitment strategies. Community engagement and partnerships with healthcare providers facilitate case identification, while standardized protocols guide zygosity determination and phenotypic data collection. Where feasible, genomic data integration is anticipated, further enhancing the registry’s scientific value.
Public Health Outreach
The public health implications of the establishing of the AfTR are substantial. Multiple births are associated with increased risks of adverse maternal and neonatal outcomes, particularly in resource-limited settings. By generating high-quality, context-specific data, the AfTR can inform clinical guidelines, health system planning, and targeted interventions. The inclusion of sociocultural variables will also enable examination of how very diverse local beliefs and practices influence outcomes among twins and their families.
Beyond maternal and child health, Africa faces a substantial burden of both infectious and noncommunicable diseases. Expanded twin registries linked to health and administrative data can support locally relevant studies of disease susceptibility, treatment response, biomarkers, and prevention strategies.
Discussion
This article presents the ATMBRF and the AfTR as complementary initiatives intended to strengthen twin research infrastructure across Africa. Their importance lies not only in expanding registry coverage, but in proposing a coordinated framework that combines standardized phenotyping, longitudinal follow-up, and secure record linkage across diverse national settings. Such an approach can help move twin research in Africa from isolated studies toward sustainable population infrastructure.
Well-characterized twin registries provide an invaluable platform for these advances by enabling repeated measures, within-pair comparisons, co-twin control analyses, and an integration of clinical, environmental, and molecular data (Odintsova et al., Reference Odintsova, Willemsen, Dolan, Hottenga, Martin, Slagboom, Ordoñana and Boomsma2018). Modern twin research increasingly combines classical genetically informative designs with omics technologies and linkage to electronic health, environmental, and administrative data, creating powerful resources for studying health and disease across the life course (Hagenbeek et al., Reference Hagenbeek, Hirzinger, Breunig, Bruins, Kuznetsov, Schut, Odintsova and Boomsma2023). Through linkage with civil registration systems, hospital records, demographic surveillance sites, and future biobank resources, the AfTR could support research on maternal and child health, growth and development, infectious and noncommunicable diseases, mental health, education, and healthy aging across diverse African settings.
The AfTR also offers an important platform for future genomic and multi-omics research in populations that remain insufficiently represented in international datasets. African populations harbor the greatest human genetic diversity and often shorter-range linkage disequilibrium patterns, creating exceptional opportunities for gene discovery and fine-mapping of causal variants. Integrating twin designs with genomic, epigenomic, transcriptomic, metabolomic, and other molecular data may improve understanding of heritability, developmental mechanisms, gene-environment interplay, causal pathways, and biomarkers relevant to African populations and beyond. Such efforts could also strengthen pharmacogenomics and precision medicine by making genetic tests and polygenic scores more accurate, equitable, and transferable for populations of African ancestry. Africa remains critically underrepresented in genotype data resources. When such resources are realized, DZ twinning and fertility genomewide association studies (GWAS) are valuable as the DZ twinning phenotype is common, and in this sense, high-prevalence DZ twinning settings offer a rare chance to pair an informative reproductive phenotype with much-needed African genomic data, improving both biological insight and ancestry diversity in (GWAS).
Implementation will require sustained funding, harmonized governance, data-protection safeguards, community engagement, and equitable partnerships. Because healthcare systems, regulatory environments, and digital infrastructures vary across countries, phased and locally adapted models of participation are likely to be most effective.
To summarize, the African Twins and Multiple Births Research Foundation and the African Twin Registry can be described as initiatives currently in development, supported by an emerging governance structure, including a board of directors, and active collaborations and partnerships. At present, the African Twin Registry is in the establishment and development phase rather than being a fully operational continental registry. The initiative has been conceived as a first step toward building a coordinated platform for twin research collaboration across Africa, including the future collection and harmonization of twin-related demographic, clinical, and biological data.
The registry is being coordinated from Lagos, Nigeria. Administrative and scientific coordination activities are currently being developed through collaborations with researchers, healthcare institutions, and academic partners across the continent. Regarding data and sample access, we are still in the early stages of establishing the governance structures, ethical approvals, consent frameworks, and infrastructure required for systematic data and biospecimen collection and management. At this stage, access to datasets and biological samples remains under development and will evolve progressively as the initiative expands.
Currently, our immediate focus is on:
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• strengthening institutional and research collaborations across Africa
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• developing frameworks for future twin data coordination and management
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• creating awareness and engagement among researchers and healthcare stakeholders
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• laying the foundation for future participant recruitment and registry expansion.
The African Twin Registry represents an initial step toward the development of a broader long-term research infrastructure. At present, the number of contributing collaborators remains limited; however, future iterations and expanded partnerships are expected to increase participation and strengthen the scope and utility of the initiative. It represents a timely and strategic step toward strengthening twin research capacity in Africa. By combining registry development with secure record linkage, longitudinal follow-up, and readiness for omics integration, these initiatives can generate locally relevant evidence while contributing to global research on health, development, and human diversity. If sustainably supported, the AfTR could become a major resource for the next generation of twin, genomic, and population science.
