Discussion

The relationship between multiple measures of childhood adversity and menarcheal timing, as well as the relationship between menarcheal timing and intended age of reproduction, was investigated in a cohort of urban English adolescent girls. Of the ten childhood adversity measures, only frequency of residential relocations and number of half/stepsisters was associated with accelerated menarche. Girls who had moved house more times were more likely to experience menarche at a given age than those who had never moved. The effect of residential relocations on menarcheal timing was cumulative. Compared with those who had never moved, relocating one to four or five or more times doubled or tripled the chance of reaching menarche, respectively. In addition, the more half/stepsisters a participant had the more likely she was to have reached menarche. This accelerating effect of half/stepsisters on menarche was present even when comparing those participants with no half/stepsisters with those with one or more. There was no association between intended reproductive timing and menarcheal timing.

The family- and neighbourhood-level childhood adversity factors that have previously been associated with menarcheal and reproductive timing were not associated with menarcheal age in this sample (see Introduction for references). However, the sample size in this study was smaller than in previous studies investigating antecedents of these reproductive life events (Moffitt et al., Reference Moffitt, Caspi, Belsky and Silva1992; Wilson & Daly, Reference Wilson and Daly1997; McCulloch, Reference McCulloch2001; Hoier, Reference Hoier2003; Padez, Reference Padez2003; Quinlan, Reference Quinlan2003; Romans et al., Reference Romans, Martin, Gendall and Herbison2003; Matchock & Susman, Reference Matchock and Susman2006; Belsky et al., Reference Belsky, Steinberg, Houts, Friedman, DeHart and Cauffman2007; Alvergne et al., Reference Alvergne, Faurie and Raymond2008; Blell et al., Reference Blell, Pollard and Pearce2008; Bogaert, Reference Bogaert2008; Johns, Reference Johns2011). Furthermore, some studies have found that it is the duration of father absence or stepfather presence that matters most (Moffitt et al., Reference Moffitt, Caspi, Belsky and Silva1992; Ellis & Garber, Reference Ellis and Garber2000; Hoier, Reference Hoier2003; Quinlan, Reference Quinlan2003; Alvergne et al., Reference Alvergne, Faurie and Raymond2008). To determine if duration of father absence had an effect on menarche in this sample a Cox regression was run including the ten childhood adversity variables but replacing the ‘Timing of father absence’ variable with a ‘Duration of father absence’ variable (duration of stepfather presence was not collected in this sample). However, the substitution of father duration made no difference to the model (details not shown).

Surprisingly, the only family structure variable that had a significant accelerating effect on menarche was the number of half/stepsisters. In this sample 57 (63%) of the participants with half/stepsister(s) (n=91) also had a half/stepbrother(s), a stepfather or both. These three variables were significantly positively correlated with each other. Thus it is possible the presence of half/stepsister(s) was acting as a proxy for exposure to unrelated males, a phenomenon observed by others to be related to early menarche (Ellis & Garber, Reference Ellis and Garber2000; Matchock & Susman, Reference Matchock and Susman2006). It is important to bear in mind that although participants were asked explicitly if a stepparent co-resided with them this was not the case for siblings, where in the interest of brevity participants were only asked about the number and type of sibling. Alternatively it is possible that having genetically dissimilar females present, such as half/stepsisters, increases intrasexual competition activating early reproductive development. Recently intrasexual competition between females has garnered attention in the animal literature for the role it plays in reproductive success (Clutton-Brock & Huchard, Reference Clutton-Brock and Huchard2013). The result observed here, that is an acceleration of menarche in the presence of half/stepsisters, is in contrast to a previous finding in this sample of a decrease in ideal age at parenthood in the presence of half/stepbrothers (Clutterbuck et al., Reference Clutterbuck, Adams and Nettle2014). It should be noted that birth order was not collected in this sample. However, it is unclear how useful this information would have been as there is little consensus within the literature on the effect of birth order on menarcheal timing (Hoier, Reference Hoier2003; Bogaert, Reference Bogaert2008, as reviewed in Matchock & Susman, Reference Matchock and Susman2006; Padez, Reference Padez2003)

To the authors' knowledge no previous studies investigating childhood adversity factors on menarcheal timing have explored the role of frequency of residential relocations. However, associations have been reported between residential relocations and both early sexual initiation and early childbearing (Crowder & Teachman Reference Crowder and Teachman2004; South et al. Reference South, Haynie and Bose2005; Ellis et al. Reference Ellis, Figueredo, Brumbach and Schlomer2009; Nettle et al. 2010b). Relocating indicates instability within the family and is likely to cause disruption to a child's social networks, which are essential in buffering against life's stressors (Cohen & Wills, Reference Cohen and Wills1985). The social networks of mothers and/or fathers are likewise potentially disrupted when relocating, increasing parental stress levels and potentially decreasing support available for the child. Certainly, in this sample, frequent residential relocation was associated with presence of a stepfather (indicating absence of at least one biological parent), increased number of half/stepsiblings and reduced feelings of family support. What is more, the effects of residential relocations on children are far reaching, including negative health outcomes, higher adult mortality rates, increased substance abuse, internalizing and externalizing symptoms and poor educational performance (Astone & McLanahan, Reference Astone and McLanahan1994; Tucker et al., Reference Tucker, Marx and Long1998; Jelleyman & Spencer, Reference Jelleyman and Spencer2008; Oishi & Schimmack, Reference Oishi and Schimmack2010). Many of these outcomes, it should be noted, are also associated with outcomes of early puberty and menarche (Van Jaarsveld et al., Reference Van Jaarsveld, Fidler, Simon and Wardle2007; Copeland et al., Reference Copeland, Shanahan, Miller, Costello, Angold and Maughan2010; Prentice & Viner, Reference Prentice and Viner2013).

The absence of an association between menarche and intended reproductive timing in this sample is perhaps not surprising given that this relationship tends to be indirect and mediated by sexual initiation (Udry, Reference Udry1979; Andersson-Ellström et al., Reference Andersson-Ellström, Forssman and Milsom1996; Deardorff et al., Reference Deardorff, Gonzales, Christopher, Roosa and Millsap2005; Dunbar et al., Reference Dunbar, Sheeder, Lezotte, Dabelea and Stevens-Simon2008; Savolainen et al., Reference Savolainen, Mason, Hughes, Ebeling, Hurtig and Taanila2012). Although it is possible that some of the sample were sexually active it is likely to be only a small proportion. In addition, although intended age at reproduction has been found to be well correlated with actual age at first birth (Nettle et al., Reference Nettle, Coall and Dickins2010), these variables are not interchangeable and intended age at reproduction tends to change with age and maturity. This was the case in this sample, where older participants tended to state an older ideal age at first birth.

To the authors' knowledge this study is the first to explore relationships between family-level and neighbourhood-level child adversity, as well as intended reproductive timing on menarcheal age. In addition, the study is unique in using a cohort of peri-pubescent participants rather than adults. Compared with study designs using retrospective recall with adults, participants in this study were reporting on current, or relatively recent, life events and circumstances allowing for potentially more reliable recall.

This study was part of a larger study that focused on recruiting girls within a specific age range and not by pubertal stage (Clutterbuck et al., Reference Clutterbuck, Adams and Nettle2014). Thus the proportion of post-menarcheal participants was small. The larger study included two ‘interest in infants’ tasks as well as the questionnaire. As such the authors were conscious to limit the number of questionnaire items to ensure participation did not prove too onerous for the young participants. Unfortunately, this meant the omission of possibly useful family structure information such as duration of stepfather presence, sibling co-residence and birth order, as discussed above. Other factors known to correlate with menarcheal timing, such as body mass index or maternal age at menarche, might also have explained some of the variation in menarcheal timing in this sample (Posner, Reference Posner2006). However, obtaining these measures was beyond the scope of this study. Additionally, it is not clear how much mother's menarcheal age would add to the overall picture of adversity and menarcheal timing because it is difficult to determine if the mother–daughter menarcheal relationship is truly genetic or due instead to intergenerational similarities in developmental environments.

Due to the age of the cohort, socioeconomic position was also omitted from the questionnaire because the authors could not be confident in the reliability of responses to questions about parental income, educational attainment or employment. However, there is support for the utility of neighbourhood socioeconomic position as a proxy for individual socioeconomic position (Adams et al., Reference Adams, Ryan and White2004). Furthermore, investigating relationships between neighbourhood environment and physical development could have positive implications for real life. Lessons on pubertal development could be brought forward in schools where early development might be more likely in female pupils. As well, because early menarche is often associated with early childbearing (see Introduction for references) it could add valuable information to the emerging debate (Johns et al., Reference Johns, Dickins and Clegg2011) that the route to reducing teenage pregnancy rates is through reducing disadvantage and inequality.

Future research should explore the circumstances that strengthen the relationship between residential relocations and menarche. Two possible avenues are critical age of exposure, outlined as important in Belsky et al.'s theory (Reference Belsky, Steinberg and Draper1991), and type of relocation such as just home, just school or both. For a child or adolescent, moving house can come with a host of uncertainty and stress. It requires the establishment of new social networks and adjustment to a new environment with all its potential risks. It often indicates disruption to home life, possibly through the break up and/or the merging of families. Rather than a benign event in a young female's life, residential relocation, in this sample, appears to be an important factor in menarche exhibiting a cumulative impact on its timing.