Prenatal stress and gender role behavior in girls and boys: a longitudinal, population study

Prenatal androgen exposure and sex-typical play behaviour: A meta-analysis of classic congenital adrenal hyperplasia studies

Thousands of non-human mammal experiments have demonstrated that early androgen exposure exerts long-lasting effects on neurobehavioural sexual differentiation. In humans, females with classic congenital adrenal hyperplasia (CAH) are exposed to unusually high concentrations of androgens prenatally, whereas prenatal concentrations of androgens in males with CAH are largely normal. The current meta-analysis included 20 independent samples and employed multi-level meta-analytic models. Consistently across all 7 male-typical and female-typical play outcomes, in the expected directions, the present study found significant and large average differences between control males and control females (gs = 0.83-2.78) as well as between females with CAH and control females (gs = 0.95-1.08), but differences between males with CAH and control males were mostly negligible and were non-significant for 6 of the 7 outcomes (gs = 0.04-0.27). These meta-analytic findings suggest that prenatal androgen exposure masculinises and defeminises play behaviour in humans. Broader implications in relation to sex chromosomes, brain development, oestrogens, socio-cognitive influences, other aspects of sex-related behavioural development, and gender nonconformity are discussed.

Early prenatal sex steroids and sex-typed play behavior at 4 years of age

During pregnancy, estrogens and testosterone influence brain development, resulting in sex-typical behavioral phenotypes. Prenatal testosterone exposure is associated with more male-typical behaviors in rodents, monkeys, and humans; however, few studies have examined the relationship between maternal sex hormones within the normal range and sex-dimorphic behaviors. In this study, we examined associations between prenatal estrogens and testosterone and sex-typical play in The Infant Development and the Environment Study (TIDES), a multicenter pregnancy cohort. We collected prenatal serum during the first trimester (mean=11.1 ± 2.6 weeks) and assessed child play behavior using the maternally completed Pre-School Activities Inventory (PSAI) at a mean age of 4.5 ± 0.3 years. This analysis includes mother-child pairs with complete data on hormones, play behavior, and covariates (n = 192 boys and 207 girls). No associations were seen between testosterone and PSAI scores in boys or girls or between estrogens and PSAI scores in boys. In girls, we observed an inverse relationship between feminine PSAI scores and both estradiol (E2) and estriol (E3) in multivariable linear regression analyses (E2: -0.11 [95% CI -0.20, -0.02]; E3: -0.44 [95% CI -0.83,-0.04]). Because the relationship between sex hormones and PSAI scores appeared nonlinear, we fit piecewise regression models to better fit the data and identify inflection points (point at which there is a significant change in slope). Piecewise regression analyses yielded inverse associations between masculine PSAI scores and estrone (E1) at values of E1 > 1340 pg/mL and E2 at values of E2 > 2870 pg/mL in girls. Further studies are needed to better understand the role of prenatal sex steroids on sexually dimorphic behavior.

Sex-typical behavior in children born preterm at very low birth weight

BACKGROUND

Perinatal events may alter psychosexual development. We aimed to assess whether a preterm birth at very low birth weight (VLBW; <1500 g) or antenatal synthetic glucocorticoids (sGC) given to the mother are associated with altered sex-typical behavior in childhood.

METHODS

Sex-typical behavior was assessed using the Pre-school Activities Inventory (PSAI) at the mean age of 4.9 years (SD 1.6) in 879 children, of whom 143 were preterm with VLBW (PT <1500 g, all exposed to sGC), 282 were preterm with birth weight ≥1500 g (PT ≥1500 g, 171 exposed to sGC), and 454 were full term (FT, 166 exposed to sGC).

RESULTS

Antenatal sGC was not associated with PSAI scores in either sex. PT <1500 g boys had less male-typical PSAI scores than other boys, even in multivariate model adjusting for age, maternal age, antenatal sGC, number of brothers and sisters, and motor or cognitive impairment. PT <1500 g girls had less female-typical PSAI scores than other girls in the multivariate model. The effect size was small (d = 0.03) for both sexes.

CONCLUSIONS

Preterm birth with VLBW is associated with reduced sex-typical behavior in childhood, which is in line with the previous data indicating altered psychosexual development in adults born preterm. Mechanisms underlying these observations are not fully understood.

IMPACT

Preterm birth is associated with reduced rates of marriage and reproduction in adulthood, but sex-typical behavior in children born preterm has not been studied before. The results of this study indicate that preterm birth with very low birth weight <1500 g is associated with reduced sex-typical behavior in childhood in both sexes. These observations are in line with the previous data indicating altered psychosexual development in adults born preterm. Mechanisms underlying these observations are not fully understood and require further studies.

Human gender development

Human gender-related behavior/psychology is shaped by a developmental system that involves numerous influences interacting over time. Understanding of the full range of elements in the system and how they interact is currently incomplete. The available evidence suggests, however, that early exposure to testosterone, postnatal socialization, e.g., by parents and peers, and self-socialization related to cognitive understanding of gender are important elements. This article focuses on prenatal and early neonatal influences of testosterone on gender-related psychological/behavioral outcomes, and contextualizes these hormonal influences within an understanding of socialization influences. There is consistent evidence that early testosterone exposure influences childhood gender role behavior, including sex-typical toy play, as well as gender identity and sexual orientation. Evidence for similar hormonal influences on spatial ability and on traits related to autism, or autistic spectrum disorder, is inconsistent. Evidence from girls exposed to elevated testosterone prenatally suggests that they experience alterations in processes of external socialization, as well as self-socialization, and that these, along with early testosterone exposure, shape gender-related outcomes.

Parent-Reports of Sex-Typed Play Preference in Preschool Children: Relationships to 2D:4D Digit Ratio and Older Siblings' Sex

Sex-typed play behavior shows large sex differences and seems to be affected by prenatal sex hormones. For example, a smaller, more male-typical ratio between the second and fourth digit length (2D:4D), a proposed marker for prenatal testosterone exposure, has been shown to be related to sex-typed play preference in childhood. Nevertheless, it is still being debated whether 2D:4D displays a stable sex difference throughout childhood, as there are few longitudinal studies. In the present study, children's 2D:4D was measured on both hands on four occasions from early infancy to early childhood (T1: 5 months, T2: 9 months, T3: 20 months, and T4: 40 months) providing the rare possibility to test the temporal stability of the sex difference. Parents completed the Preschool Activities Inventory at T4 and reported on the number of older brothers and sisters as a measure for socialization influences. Parents described boys as playing more masculine and less feminine than girls. Boys had smaller 2D:4D than girls at all measurements (T1-T4) and on both hands (right/left). Nevertheless, 2D:4D increased significantly from T3 to T4 in both sexes. Girls, but not boys, who were described as playing more masculine and less feminine had more masculine 2D:4D ratios at T1-T4 on both hands (except for right 2D:4D at T2 and T3) and had more older brothers and fewer older sisters. These data underline the stability of the sex difference in 2D:4D and show the importance of both biological and social influences on sex-typed play behavior.

Prenatal anxiety, breastfeeding and child growth and puberty: linking evolutionary models with human cohort studies

Background: Stress experienced by mothers during pregnancy can have both immediate and long-term effects on child development, potentially mediated by breastfeeding.Aim: Using a UK birth cohort study, we asked how maternal stress relates to breastfeeding and consequences for growth and puberty onset.Subjects and methods: We analysed data from the Avon Longitudinal Study of Parents and Children, collected via questionnaires and clinic visits (N: 698-8,506). We used reports of prenatal anxiety, breastfeeding, early growth and age at menarche or first voice change. Confounding by maternal age, parity, smoking, education and body mass index (BMI) was considered.Results: Mothers with higher levels of reported anxiety were less likely to breastfeed (Odds ratio (OR): 0.83, 95% confidence interval (CI): 0.71, 0.97). Breastfed infants had slower growth before weaning, although growth differences were unclear thereafter. Being breastfed for more than six months was associated with later puberty onset in females (2.76 months later than non-breastfed; CI: 0.9, 4.63), although the association was attenuated by confounders and BMI (1.51 months, CI: -0.38, 3.40). No association between breastfeeding and puberty onset in males was found.Conclusion: Our studies fit results shown previously, and we consider these in light of evolutionary life history theory while discussing key challenges in such an approach.

2D:4D Suggests a Role of Prenatal Testosterone in Gender Dysphoria

Gender dysphoria (GD) reflects distress caused by incongruence between one's experienced gender identity and one's natal (assigned) gender. Previous studies suggest that high levels of prenatal testosterone (T) in natal females and low levels in natal males might contribute to GD. Here, we investigated if the 2D:4D digit ratio, a biomarker of prenatal T effects, is related to GD. We first report results from a large Iranian sample, comparing 2D:4D in 104 transwomen and 89 transmen against controls of the same natal sex. We found significantly lower (less masculine) 2D:4D in transwomen compared to control men. We then conducted random-effects meta-analyses of relevant studies including our own (k = 6, N = 925 for transwomen and k = 6, N = 757 for transmen). In line with the hypothesized prenatal T effects, transwomen showed significantly feminized 2D:4D (d ≈ 0.24). Conversely, transmen showed masculinized 2D:4D (d ≈ - 0.28); however, large unaccounted heterogeneity across studies emerged, which makes this effect less meaningful. These findings support the idea that high levels of prenatal T in natal females and low levels in natal males play a part in the etiology of GD. As we discuss, this adds to the evidence demonstrating the convergent validity of 2D:4D as a marker of prenatal T effects.

The biological basis of sexual orientation: How hormonal, genetic, and environmental factors influence to whom we are sexually attracted

Humans develop relatively stable attractions to sexual partners during maturation and present a spectrum of sexual orientation from homosexuality to heterosexuality encompassing varying degrees of bisexuality, with some individuals also displaying asexuality. Sexual orientation represents a basic life phenomenon for humans. However, the molecular mechanisms underlying these diverse traits of sexual orientation remain highly controversial. In this review, we systematically discuss recent advancements in sexual orientation research, including those related to measurements and associated brain regions. Current findings regarding sexual orientation modulation by hormonal, genetic, maternal immune system, and environmental factors are summarized in both human and model systems. We also emphasize that future studies should recognize the differences between males and females and pay more attention to minor traits and the epigenetic regulation of sexual orientation. A comprehensive view of sexual orientation may promote our understanding of the biological basis of sex, and that of human reproduction, and evolution.

Neuroscience and Sex/Gender: Looking Back and Forward

Phoenix et al. (1959) reported that treating pregnant guinea pigs with testosterone had enduring effects on the sex-related behavior of their female offspring. Since then, similar enduring effects of early testosterone exposure have been found in other species, including humans, and for other behaviors that show average sex differences. In humans, the affected outcomes include gender identity, sexual orientation, and children's sex-typical play behavior. The evidence linking early testosterone exposure to sex-typed play is particularly robust, and sex-typed play is also influenced by many other factors, including socialization by parents and peers and self-socialization, based on cognitive understanding of gender. In addition to influencing behavior, testosterone and hormones produced from testosterone affect mammalian brain structure. Studies using human autopsy material have found some sex differences in the human brain similar to those seen in other species, and have reported that some brain sex differences correlate with sexual orientation or gender identity, although the causes of these brain/behavior relationships are unclear. Studies that have imaged the living human brain have found only a small number of sex differences, and these differences are generally small in magnitude. In addition, they have not been linked to robust psychological or behavioral sex differences. Future research might benefit from improved imaging technology, and attention to other brain characteristics. In addition, it might usefully explore how different types of factors, such as early testosterone exposure and parental socialization, work together in the developmental system that produces sex/gender differences in human brain and behavior.

Birth order and recalled childhood gender nonconformity in Samoan men and fa'afafine

Having a greater than average number of older biological brothers is a robust correlate of male androphilia (i.e., sexual attraction and arousal to adult males). Previous investigations have sought to understand whether this fraternal birth order (FBO) effect is also systematically related to recalled indicators of childhood gender nonconformity (CGN). However, these investigations have relied on data from low-fertility Western populations in which expressions of femininity in male children are routinely stigmatized and consequently, suppressed. The present study examined the FBO effect (among other sibship characteristics) and recalled indicators of CGN in Samoa, a high-fertility population, whose members are relatively tolerant of male femininity. Indeed, Samoans identify feminine androphilic males as belonging to an alternative gender category, known locally as fa'afafine. The present study compared the sibship characteristics of 231 fa'afafine and 231 opposite-sex attracted men from Samoa, as well as how these characteristics related to recalled CGN. Results replicated the well-established FBO effect for predicting male sexual orientation, with each older brother increasing the odds of being androphilic by 21%. However, no relationship was found between the number of older brothers (or other siblings) a participant had and their recalled CGN. Although fa'afafine reported significantly more CGN than Samoan men, CGN did not mediate the FBO effect, nor did the FBO effect and CGN interact to predict male sexual orientation. These findings are consistent with previous studies suggesting that the FBO effect is associated with male sexual orientation, but not childhood female-typical gender expression among androphilic males.

Evolution of Sex Differences in Trait- and Age-Specific Vulnerabilities

Traits that facilitate competition for reproductive resources or that influence mate choice generally have a heightened sensitivity to stressors. They have evolved to signal resilience to infectious disease and nutritional and social stressors, and they are compromised by exposure to man-made toxins. Although these traits can differ from one species or sex to the next, an understanding of the dynamics of competition and choice can in theory be used to generate a priori predictions about sex-, age-, and trait-specific vulnerabilities for any sexually reproducing species. I provide a review of these dynamics and illustrate associated vulnerabilities in nonhuman species. The age- and sex-specific vulnerability of such traits is then illustrated for stressor-related disruptions of boys’ and girls’ physical growth and play behavior, as well as for aspects of boys’ and girls’ and men’s and women’s personality, language, and spatial abilities. There is much that remains to be determined, but enough is now known to reframe trait sensitivity in ways that will allow scientists and practitioners to better identify and understand vulnerable human traits, and eventually ameliorate or prevent their expression.

Maternal stress before and during pregnancy and subsequent infertility in daughters: a nationwide population-based cohort study

STUDY QUESTION

Is maternal stress following the death of a close relative before or during pregnancy associated with the risk of infertility in daughters?

SUMMARY ANSWER

Compared with unexposed women, women whose mothers had experienced bereavement stress during, or in the year before, pregnancy had a similar risk of infertility overall, but those exposed to maternal bereavement during the first trimester had a higher risk of infertility.

WHAT IS KNOWN ALREADY

Animal studies have shown that prenatal maternal stress results in reduced offspring fertility. In humans, there is evidence that girls who have been prenatally exposed to stress have a more masculine behaviour and a slight delay in having their first child.

STUDY DESIGN, SIZE AND DURATION

This population-based cohort study, included 660 099 females born in Denmark between 1 January 1973 and 31 December 1993 to mothers of Danish origin and with at least one living relative in the exposure window, and followed the women through 31 December 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Overall, 13 334 women (2.0%) were considered prenatally exposed to stress because their mother had lost a spouse/partner, a child, a parent, or a sibling during pregnancy or in the year before conception. Infertility was defined as any record of infertility treatment or diagnosis of female infertility. We considered the date of onset as the date of the first appearance of any such record. The association between exposure and outcome was examined using hazard ratios (HR) with 95% confidence intervals (CI).

MAIN RESULTS AND THE ROLE OF CHANCE

Based on our definition, 40 052 (6.5%) women were infertile in the follow-up period (median age at the end of follow-up: 26.7 years, maximum age: 39 years). Overall, prenatal exposure to maternal stress was not associated with risk of infertility (adjusted HR = 1.04 [CI: 0.95-1.14]). However, women prenatally exposed during the first trimester had a higher estimated risk (adjusted HR = 1.40 [CI: 1.05-1.86]). These findings were consistent in subgroups defined by the relationship of the mother to the deceased and in several sensitivity analyses, including a sibling-matched analysis, and in analyses restricted to women who were married or cohabitating with a man, or to women born at term.

LIMITATIONS, REASONS FOR CAUTION

We did not have a direct measure of stress, but bereavement due to death of a close relative is likely to be very stressful. We based the timing of exposure on the date of the death of the family member, although the stress may well have started earlier. Infertility was also defined indirectly, and many women in the cohort were too young at the end of the follow-up to have been diagnosed. However, misclassification of the outcome was most likely non-differential, and the similar results from all sensitivity analyses suggest that it is unlikely that the effect observed in first trimester exposure would be due to chance.

WIDER IMPLICATIONS OF THE FINDINGS

Prenatal exposure to maternal stress in the first trimester may affect the later fecundity of daughters.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by a grant from the European Research Council (ERC-2010-StG-260242-PROGEURO) to the ProgEuro project (http://progeuro.au.dk). O.P.-R. is partly supported by a fellowship from Aarhus University and a travel grant from Oticon Fonden. The authors report no conflict of interests.

Multimodal sex-related differences in infant and in infant-directed maternal behaviors during months three through twelve of development

Using the concepts of sensory and affective experience, this work relates the concepts of socialization and cognitive development to the embodiment of gender in the human infant. Evidence obtained from biweekly observations from 30 children and their mothers observed from age 3 months to age 12 months revealed measurable sex-related differences in how mothers handle and touch their infants. This work offers novel approaches to visualizing combinations of behaviors with the aim of encouraging researchers to think in terms of suites of action rather than singular sensory or motor systems. New avenues of research into the mechanisms which produce sex-related differences in behavior are suggested.

Exposure to prenatal life events stress is associated with masculinized play behavior in girls

Previous research has shown that prenatal exposure to endocrine-disrupting chemicals can alter children's neurodevelopment, including sex-typed behavior, and that it can do so in different ways in males and females. Non-chemical exposures, including psychosocial stress, may disrupt the prenatal hormonal milieu as well. To date, only one published study has prospectively examined the relationship between exposure to prenatal stress and gender-specific play behavior during childhood, finding masculinized play behavior in girls who experienced high prenatal life events stress, but no associations in boys. Here we examine this question in a second prospective cohort from the Study for Future Families. Pregnant women completed questionnaires on stressful life events during pregnancy, and those who reported one or more events were considered "stressed". Families were recontacted several years later (mean age of index child: 4.9 years), and mothers completed a questionnaire including the validated Preschool Activities Inventory (PSAI), which measures sexually dimorphic play behavior. In sex-stratified analyses, after adjusting for child's age, parental attitudes toward gender-atypical play, age and sex of siblings, and other relevant covariates, girls (n=72) exposed to prenatal life events stress had higher scores on the PSAI masculine sub-scale (β=3.48, p=0.006) and showed a trend toward higher (more masculine) composite scores (β=2.63, p=0.08). By contrast, in males (n=74), there was a trend toward an association between prenatal stress and higher PSAI feminine sub-scale scores (β=2.23, p=0.10), but no association with masculine or composite scores. These data confirm previous findings in humans and animal models suggesting that prenatal stress is a non-chemical endocrine disruptor that may have androgenic effects on female fetuses and anti-androgenic effects on male fetuses.

Mechanisms of prenatal programing: identifying and distinguishing the impact of steroid hormones

Developmental programing is gaining considerable leverage as a conceptual framework for understanding individual variability in human behavioral and somatic health. The current mini-review examines some of the key conceptual and methodological challenges for developmental programing research focused on fetal sex steroid exposure and physical, behavioral, physiological, and health outcomes. Specifically, we consider the bases for focusing on sex steroids, methods for assessing prenatal steroid hormone exposure, confounding factors, and the most relevant postnatal outcomes. We conclude with a brief consideration, based on current knowledge, of the applications of the existing findings for further research and practice.

Gender-Typed Play Behavior in Early Childhood: Adopted Children with Lesbian, Gay, and Heterosexual Parents

This study examined whether the gender-typed play of young children varies as a function of family structure. Using a sample of 126 couples (44 lesbian couples, 34 gay male couples, and 48 heterosexual couples) located throughout the United States, with an adopted child between the age of 2 and 4 years old (mean = 2.5 years), we examined parent reports of children's gender-typed play behavior utilizing the Pre-School Activities Inventory (PSAI; Golombok & Rust, 1993). Findings revealed that the perceived play behaviors of boys and girls in same-gender parent families were more similar (i.e., less gender-stereotyped) than the perceived play behavior of boys and girls in heterosexual-parent families (which were more divergent; that is, gender-stereotyped). Sons of lesbian mothers were less masculine in their play behavior than sons of gay fathers and sons of heterosexual parents. Our findings have implications for researchers who study gender development in children and adolescents.

Testosterone measured in infancy predicts subsequent sex-typed behavior in boys and in girls

The testes are active during gestation, as well as during early infancy. Testosterone elevation during fetal development has been shown to play a role in human neurobehavioral sexual differentiation. The role of early postnatal gonadal activation in human psychosexual development is largely unknown, however. We measured testosterone in 48 full term infants (22 boys, 26 girls) by monthly urinary sampling from day 7 postnatal to age 6 months, and related the area under the curve (AUC) for testosterone during the first 6 months postnatal to subsequent sex-typed behavior, at the age of 14 months, using the Pre-School Activities Inventory (PSAI), and playroom observation of toy choices. In boys, testosterone AUC correlated significantly with PSAI scores (Spearman's rho = 0.54, p = 0.04). In addition, play with a train and with a baby doll showed the anticipated sex differences, and play with the train correlated significantly and positively with testosterone AUC in girls (Spearman's rho = 0.43, p = 0.05), while play with the doll correlated significantly and negatively with testosterone AUC in boys (Spearman's rho = -0.48, p < 0.03). These results may support a role for testosterone during early infancy in human neurobehavioral sexual differentiation.

Early-life soy exposure and gender-role play behavior in children

BACKGROUND

Soy-based infant formula contains high levels of isoflavones. These estrogen-like compounds have been shown to induce changes in sexually dimorphic behaviors in animals exposed in early development.

OBJECTIVE

We examined gender-role play behavior in relation to soy-based and non-soy-based infant feeding methods among children in the Avon Longitudinal Study of Parents and Children.

METHODS

We studied 3,664 boys and 3,412 girls. Four exposure categories were created using data from questionnaires administered at 6 and 15 months postpartum: primarily breast, early formula (referent), early soy, and late soy. Gender-role play behavior was assessed using the Pre-School Activities Inventory (PSAI). Associations between infant feeding and PSAI scores at 42 months of age were assessed using linear regression. Post hoc analyses of PSAI scores at 30 and 57 months were also conducted.

RESULTS

Early-infancy soy use was reported for approximately 2% of participants. Mean [95% confidence interval (CI)] PSAI scores at 42 months were 62.3 (62.0, 62.6) and 36.9 (36.6, 37.2) for boys and girls, respectively. After adjustment, early soy (vs. early formula) feeding was associated with higher (less feminine) PSAI scores in girls (β = 2.66; 95% CI: 0.19, 5.12) but was not significantly associated with PSAI scores in boys. The association between soy exposure and PSAI scores in girls was substantially attenuated at 30 and 57 months.

CONCLUSIONS

Although not consistent throughout childhood, early-life soy exposure was associated with less female-typical play behavior in girls at 42 months of age. Soy exposure was not significantly associated with play behavior in boys.

Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior

Both sexual orientation and sex-typical childhood behaviors, such as toy, playmate and activity preferences, show substantial sex differences, as well as substantial variability within each sex. In other species, behaviors that show sex differences are typically influenced by exposure to gonadal steroids, particularly testosterone and its metabolites, during early development (prenatally or neonatally). This article reviews the evidence regarding prenatal influences of gonadal steroids on human sexual orientation, as well as sex-typed childhood behaviors that predict subsequent sexual orientation. The evidence supports a role for prenatal testosterone exposure in the development of sex-typed interests in childhood, as well as in sexual orientation in later life, at least for some individuals. It appears, however, that other factors, in addition to hormones, play an important role in determining sexual orientation. These factors have not been well-characterized, but possibilities include direct genetic effects, and effects of maternal factors during pregnancy. Although a role for hormones during early development has been established, it also appears that there may be multiple pathways to a given sexual orientation outcome and some of these pathways may not involve hormones.

Sex-related variation in human behavior and the brain

Male and female fetuses differ in testosterone concentrations beginning as early as week 8 of gestation. This early hormone difference exerts permanent influences on brain development and behavior. Contemporary research shows that hormones are particularly important for the development of sex-typical childhood behavior, including toy choices, which until recently were thought to result solely from sociocultural influences. Prenatal testosterone exposure also appears to influence sexual orientation and gender identity, as well as some, but not all, sex-related cognitive, motor and personality characteristics. Neural mechanisms responsible for these hormone-induced behavioral outcomes are beginning to be identified, and current evidence suggests involvement of the hypothalamus and amygdala, as well as interhemispheric connectivity, and cortical areas involved in visual processing.

Maternal corticosterone but not testosterone level is associated with the ratio of second-to-fourth digit length (2D:4D) in field vole offspring (Microtus agrestis)

The steroid environment encountered by a foetus can strongly affect its post-natal physiology and behaviour. It has been proposed that steroid concentrations experienced in utero could be estimated from adults by measuring their second-to-fourth digit length ratio (2D:4D). However, there is still little direct evidence that intra-uterine steroid levels affect individual 2D:4D. We examined whether maternal pre-pregnancy testosterone and corticosterone levels (as estimates of intra-uterine testosterone and corticosterone exposure) affected the 2D:4D of pups in non-domesticated field voles (Microtus agrestis), measured by X-rays at the age of weaning (21 days). Furthermore, for the first time in a non-human species, we studied whether testosterone and corticosterone levels correlated with 2D:4D in adult females. We found that the maternal pre-pregnancy level of testosterone was not associated with offspring 2D:4D in either the left or the right paw. Instead, maternal pre-pregnancy corticosterone level was positively correlated with offspring 2D:4D in the right paw, but unrelated to 2D:4D in the left paw. In addition, the 2D:4D of adult females was not associated with either their circulating testosterone or corticosterone levels. Our results suggest that in field voles maternally administered testosterone is not a major determinant of offspring 2D:4D, whereas maternal stress appears to account for some of the variation in the 2D:4D of their offspring.

Physical and mental health outcomes of prenatal maternal stress in human and animal studies: a review of recent evidence

Prenatal maternal stress (PNMS) has been linked with adverse health outcomes in the offspring through experimental studies using animal models and epidemiological studies of human populations. The purpose of this review article is to establish a parallel between animal and human studies, while focusing on methodological issues and gaps in knowledge. The review examines the quality of recent evidence for prevailing PNMS theoretical models, namely the biopsychosocial model for adverse pregnancy outcomes and the fetal programming model for chronic diseases. The investigators used PubMed (2000-06) to identify recently published original articles in the English language literature. A total of 103 (60 human and 43 animal) studies were examined. Most human studies originated from developed countries, thus limiting generalisability to developing nations. Most animal studies were conducted on non-primates, rendering extrapolation of findings to pregnant women less straightforward. PNMS definition and measurement were heterogeneous across studies examining similar research questions, thus precluding the conduct of meta-analyses. In human studies, physical health outcomes were often restricted to birth complications while mental health outcomes included postnatal developmental disorders and psychiatric conditions in children, adolescents and adults. Diverse health outcomes were considered in animal studies, some being useful models for depression, schizophrenia or attention deficit hyperactivity disorder in human populations. The overall evidence is consistent with independent effects of PNMS on perinatal and postnatal outcomes. Intervention studies and large population-based cohort studies combining repeated multi-dimensional and standardised PNMS measurements with biomarkers of stress are needed to further understand PNMS aetiology and pathophysiology in human populations.

Effects of prenatal stress on sexual partner preference in mice

Three-month old, male Swiss Webster mice were born to either control dams or dams who had been prenatally stressed with light, heat, noise and handling during the last week of gestation. As adults, male offspring were tested on sexual partner preference and sexual behavior (mounting, intromissions and lordosis) with a sexually experienced male stimulus animal and a stimulus estrous female. In comparison to males born to control dams, prenatally stressed males showed a sexual partner preference for the sexually active male as demonstrated by a negative partner preference score, more and longer visits to the male's compartment, fewer and shorter visits to the female's compartment and longer latencies to and lower frequencies of mounts and intromissions of females. In addition, stressed males showed a greater frequency of lordosis and a higher lordosis quotient than did control males. This study is the first to investigate the effects of prenatal stress alone, without hormonal manipulation, on sexual partner preference using both a partner preference paradigm and measures of sexual behavior such as mounting, intromissions and lordosis. These findings support the suggestion that prenatal stress alone is enough to significantly affect sexual partner preference in male mice.

Maternal psychological distress during pregnancy in relation to child development at age two

Concern exists that a constellation of negative maternal emotions during pregnancy generates persistent negative consequences for child development. Maternal reports of anxiety, pregnancy-specific and nonspecific stress, and depressive symptoms were collected during mid-pregnancy and at 6 weeks and 24 months after birth in a sample of healthy women with low risk pregnancies. Developmental assessment and cardiac vagal tone monitoring were administered to 94 children at age 2. Higher levels of prenatal anxiety, nonspecific stress, and depressive symptoms were associated with more advanced motor development in children after postnatal control for each psychological measure; anxiety and depression were also significantly and positively associated with mental development. Mild to moderate levels of psychological distress may enhance fetal maturation in healthy populations.

Two monozygotic twin pairs discordant for female-to-male transsexualism

Two monozygotic female twin pairs discordant for transsexualism are described. These reports double the number of such case studies in the current scientific literature. Interviews with the twins and their families indicated that unusual medical and life history factors did not play causal roles. However, inspection of medical records for one transsexual twin suggested that some early life experiences may have exacerbated tendencies toward male gender identification. In both pairs, the twins' gender identity differences emerged early, consistent with, but not proof of, co-twin differences in prenatal hormonal influences. The identification of additional discordant MZ female twin pairs can advance biological and psychological understanding of transsexualism. Suggestions for future research, based upon findings from these two twin pairs and from studies of female-to-male transsexuals, are provided.

Measurement of psychosexual differentiation

Since the early 1990s, there has been a surge in interest in the study of infants, children, adolescents, and adults with physical intersex conditions or other congenital conditions that affect, among other things, the configuration of the external genitalia. Regarding psychologic evaluation, an important aspect of both short-term and long-term outcome concerns gender differentiation. This article provides an overview of various measures pertaining to gender identity, gender role, and sexual orientation that have been used in assessment studies of samples of either children and adults with gender identity disorder and/or children and adults with various physical intersex conditions. All of the measures have good psychometric quality although some have been studied more systematically than others. It is hoped that this overview will provide a template for the new generation of studies that are looking at both gender development and sexual orientation in people born with physical intersex conditions.

Genetic and Environmental Influences on Sex-Typed Behavior During the Preschool Years

The genetic and environmental etiologies of sex-typed behavior were examined during the preschool years in a sample of 3,990 three- to four-year-old twin and non-twin sibling pairs. Results showed moderate genetic and significant shared environmental influence for boys and substantial genetic and moderate shared environmental influence for girls. For both boys and girls, twin-specific shared environmental effects contributed to twins' similarity in gender role behavior and accounted for approximately 22% of the shared environmental variance. These findings extend previous research conducted with older samples by showing not only important genetic contributions to gender role behavior but also an important role for shared environment. The inclusion of non-twin siblings showed that some of the shared environmental influence is specific to twins.

Prenatal sex hormone effects on child and adult sex-typed behavior: methods and findings

There is now good evidence that human sex-typed behavior is influenced by sex hormones that are present during prenatal development, confirming studies in other mammalian species. Most of the evidence comes from clinical populations, in which prenatal hormone exposure is atypical for a person's sex, but there is increasing evidence from the normal population for the importance of prenatal hormones. In this paper, we briefly review the evidence, focusing attention on the methods used to study behavioral effects of prenatal hormones. We discuss the promises and pitfalls of various types of studies, including those using clinical populations (concentrating on those most commonly studied, congenital adrenal hyperplasia, androgen insensitivity syndrome, ablatio penis, and cloacal exstrophy), direct measures of hormones in the general population (assayed through umbilical cord blood, amniotic fluid, and maternal serum during pregnancy), and indirect measures of hormones in the general population (inferred from intrauterine position and biomarkers such as otoacoustic emissions, finger length ratios, and dermatoglyphic asymmetries). We conclude with suggestions for interpreting and conducting studies of the behavioral effects of prenatal hormones.

Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men

Meta-analysis of aggregate data from 14 samples representing 10,143 male subjects shows that homosexuality in human males is predicted by higher numbers of older brothers, but not by higher numbers of older sisters, younger brothers, or younger sisters. The relation between number of older brothers and sexual orientation holds only for males. This phenomenon has therefore been called the fraternal birth order effect. Research on birth order, birth weight, and sexual orientation suggests that the developmental pathway to homosexuality initiated by older brothers operates during prenatal life. Calculations assuming a causal relation between older brothers and sexual orientation have estimated the proportion of homosexual men who owe their sexual orientation to fraternal birth order at 15% in one study and 29% in another. The maternal immune hypothesis proposes that the fraternal birth order effect reflects the progressive immunization of some mothers to male-specific antigens by each succeeding male fetus and the increasing effects of such immunization on sexual differentiation of the brain in each succeeding male fetus. There are at least three possible mechanisms by which the mother's immune response could influence the fetus: the transfer of anti-male antibodies across the placenta from the maternal into the fetal compartment, the transfer of maternal cytokines across the placenta, and maternal immune reactions affecting the placenta itself. This hypothesis is consistent with recent studies showing that the quantity of fetal cells that enter the maternal circulation is greater than previously thought, and that the number of male-specific proteins encoded by Y-chromosome genes is greater than previously thought.

Androgen and psychosexual development: core gender identity, sexual orientation and recalled childhood gender role behavior in women and men with congenital adrenal hyperplasia (CAH)

We assessed core gender identity, sexual orientation, and recalled childhood gender role behavior in 16 women and 9 men with CAH and in 15 unaffected female and 10 unaffected male relatives, all between the ages of 18 and 44 years. Women with congenital adrenal hyperplasia (CAH) recalled significantly more male-typical play behavior as children than did unaffected women, whereas men with and without CAH did not differ. Women with CAH also reported significantly less satisfaction with the female sex of assignment and less heterosexual interest than did unaffected women. Again, men with CAH did not differ significantly from unaffected men in these respects. Our results for women with CAH are consistent with numerous prior reports indicating that girls with CAH show increased male-typical play behavior. They also support the hypotheses that these women show reduced heterosexual interest and reduced satisfaction with the female sex of assignment. Our results for males are consistent with most prior reports that boys with CAH do not show a general alteration in childhood play behavior. In addition, they provide initial evidence that core gender identity and sexual orientation are unaffected in men with CAH. Finally, among women with CAH, we found that recalled male-typical play in childhood correlated with reduced satisfaction with the female gender and reduced heterosexual interest in adulthood. Although prospective studies are needed, these results suggest that those girls with CAH who show the greatest alterations in childhood play behavior may be the most likely to develop a bisexual or homosexual orientation as adults and to be dissatisfied with the female sex of assignment.

Sex Steroids and Human Behavior: Prenatal Androgen Exposure and Sex-Typical Play Behavior in Children

Gonadal hormones, particularly androgens, direct certain aspects of brain development and exert permanent influences on sex-typical behavior in nonhuman mammals. Androgens also influence human behavioral development, with the most convincing evidence coming from studies of sex-typical play. Girls exposed to unusually high levels of androgens prenatally, because they have the genetic disorder, congenital adrenal hyperplasia (CAH), show increased preferences for toys and activities usually preferred by boys, and for male playmates, and decreased preferences for toys and activities usually preferred by girls. Normal variability in androgen prenatally also has been related to subsequent sex-typed play behavior in girls, and nonhuman primates have been observed to show sex-typed preferences for human toys. These findings suggest that androgen during early development influences childhood play behavior in humans at least in part by altering brain development.