The human sex ratio from conception to birth

Effects of hazardous chemicals on secondary sex ratio: A comprehensive review

The secondary sex ratio (SSR), defined as the ratio of male to female offspring at birth, has garnered significant scientific interest due to its potential impact on population dynamics and evolution. In recent years, there has been a growing concern regarding the potential consequences of environmental chemicals on the SSR, given their widespread exposure and potential enduring ramifications on the reproductive system. While SSR serves as an indicator of health, ongoing research and scientific inquiry are being conducted to explore the potential relationship between chemicals and offspring ratio. Although some studies have suggested a possible correlation, others have yielded inconclusive results, indicating that the topic is intricate and still needs to be elucidated. The precise mechanism by which chemical agents exert their influence on the SSR remains ambiguous, with disruption of the endocrine system being a prominent justification. In light of the complex interplay between chemical exposure and SSR, the present review aims to comprehensively examine and synthesize existing scientific literature to gain a deeper understanding of how specific chemical exposures may impact SSR. Insights into chemical hazards that shift SSR patterns or trends could guide prevention strategies, including legislative bans of certain chemicals, to minimize environmental and public health risks.

Female-biased birth sex ratio in a female dispersal primate suggests local resource competition

Group living may entail local resource competition (LRC) which can be reduced if the birth sex ratio (BSR) is biased towards members of the dispersing sex who leave the group and no longer compete locally with kin. In primates, the predicted relationship between dispersal and BSR is generally supported although data for female dispersal species are rare and primarily available from captivity. Here, we present BSR data for Phayre's leaf monkeys (Trachypithecus phayrei crepusculus) at the Phu Khieo Wildlife Sanctuary, Thailand (N = 104). In this population, nearly all natal females dispersed, while natal males stayed or formed new groups nearby. The slower reproductive rate in larger groups suggests that food can be a limiting resource. In accordance with LRC, significantly more females than males were born (BSR 0.404 males/all births) thus reducing future competition with kin. This bias was similar in 2-year-olds (no sex-differential mortality). It became stronger in adults, supporting our impression of particularly fierce competition among males. To better evaluate the importance of BSR, more studies should report sex ratios throughout the life span, and more data for female dispersal primates need to be collected, ideally for multiple groups of different sizes and for several years.

Sex-specific effects of environmental temperature during gestation on fluctuating asymmetry in deciduous teeth

OBJECTIVES

External environmental heat exposure during gestation impacts the physiology of human development in utero, but evidence for these impacts has not yet been explored in dentition. We examined deciduous teeth for fluctuating asymmetry (FA), a measure of developmental instability, together with gestational environmental temperature data drawn from historical weather statistics.

MATERIALS AND METHODS

We measured dental casts from the longitudinal Burlington Growth Study, representing 172 participants (ages 3-6 years) with health records. FA was calculated from crown dimensions and intercuspal distances that develop during gestation. Multiple regression separated by sex (nfemale = 81) examined the effects of mean temperatures in each trimester, controlling for birth year.

RESULTS

In females, increased temperatures during the first trimester are significantly associated with an increase in FA (p = 0.03), specifically during the second and third prenatal months (p = 0.03). There is no relationship between temperature and FA for either sex in the second or third trimesters, when enamel is formed.

DISCUSSION

Dental instability may be sensitive to temperature in the first trimester in females during the scaffolding of crown shape and size in the earliest stages of tooth formation. Sexual dimorphism in growth investment strategies may explain the differences in results between males and females. Using enduring dental characteristics, these results advance our understanding of the effects of temperature on fetal physiology within a discrete period.

Impact of sex, race, and social determinants of health on neonatal outcomes

Despite the global improvements in neonatal outcomes, mortality and morbidity rates among preterm infants are still unacceptably high. Therefore, it is crucial to thoroughly analyze the factors that affect these outcomes, including sex, race, and social determinants of health. By comprehending the influence of these factors, we can work towards reducing their impact and enhancing the quality of neonatal care. This review will summarize the available evidence on sex differences, racial differences, and social determinants of health related to neonates. This review will discuss sex differences in neonatal outcomes in part I and racial differences with social determinants of health in part II. Research has shown that sex differences begin to manifest in the early part of the pregnancy. Hence, we will explore this topic under two main categories: (1) Antenatal and (2) Postnatal sex differences. We will also discuss long-term outcome differences wherever the evidence is available. Multiple factors determine health outcomes during pregnancy and the newborn period. Apart from the genetic, biological, and sex-based differences that influence fetal and neonatal outcomes, racial and social factors influence the health and well-being of developing humans. Race categorizes humans based on shared physical or social qualities into groups generally considered distinct within a given society. Social determinants of health (SDOH) are the non-medical factors that influence health outcomes. These factors can include a person's living conditions, access to healthy food, education, employment status, income level, and social support. Understanding these factors is essential in developing strategies to improve overall health outcomes in communities.

A developmental framework for understanding the influence of sex and gender on health: Pediatric pain as an exemplar

Sex differences are a robust finding in many areas of adult health, including cardiovascular disease, psychiatric disorders, and chronic pain. However, many sex differences are not consistently observed until after the onset of puberty. This has led to the hypothesis that hormones are primary contributors to sex differences in health outcomes, largely ignoring the relative contributions of early developmental influences, emerging psychosocial factors, gender, and the interaction between these variables. In this paper, we argue that a comprehensive understanding of sex and gender contributions to health outcomes should start as early as conception and take an iterative biopsychosocial-developmental perspective that considers intersecting social positions. We present a conceptual framework, informed by a review of the literature in basic, clinical, and social science that captures how critical developmental stages for both sex and gender can affect children's health and longer-term outcomes. The literature on pediatric chronic pain is used as a worked example of how the framework can be applied to understanding different chronic conditions.

Overexpression of Human sFLT1 in the Spongiotrophoblast Is Sufficient to Induce Placental Dysfunction and Fetal Growth Restriction in Transgenic Mice

Preeclampsia (PE) is characterized by maternal hypertension and placental dysfunction, often leading to fetal growth restriction (FGR). It is associated with an overexpression of the anti-angiogenic sFLT1 protein, which originates from the placenta and serves as a clinical biomarker to predict PE. To analyze the impact of sFLT1 on placental function and fetal growth, we generated transgenic mice with placenta-specific human sFLT1 (hsFLT1) overexpression. Immunohistochemical, morphometrical, and molecular analyses of the placentas on 14.5 dpc and 18.5 dpc were performed with a focus on angiogenesis, nutrient transport, and inflammation. Additionally, fetal development upon placental hsFLT1 overexpression was investigated. Dams exhibited a mild increase in serum hsFLT1 levels upon placental hsFLT1 expression and revealed growth restriction of the fetuses in a sex-specific manner. Male FGR fetuses expressed higher amounts of placental hsFLT1 mRNA compared to females. FGR placentas displayed an altered morphology, hallmarked by an increase in the spongiotrophoblast layer and changes in labyrinthine vascularization. Further, FGR placentas showed a significant reduction in placental glycogen storage and nutrient transporter expression. Moreover, signs of hypoxia and inflammation were observed in FGR placentas. The transgenic spongiotrophoblast-specific hsFLT1 mouse line demonstrates that low hsFLT1 serum levels are sufficient to induce significant alterations in fetal and placental development in a sex-specific manner.

Highly cooperative chimeric super-SOX induces naive pluripotency across species

Our understanding of pluripotency remains limited: iPSC generation has only been established for a few model species, pluripotent stem cell lines exhibit inconsistent developmental potential, and germline transmission has only been demonstrated for mice and rats. By swapping structural elements between Sox2 and Sox17, we built a chimeric super-SOX factor, Sox2-17, that enhanced iPSC generation in five tested species: mouse, human, cynomolgus monkey, cow, and pig. A swap of alanine to valine at the interface between Sox2 and Oct4 delivered a gain of function by stabilizing Sox2/Oct4 dimerization on DNA, enabling generation of high-quality OSKM iPSCs capable of supporting the development of healthy all-iPSC mice. Sox2/Oct4 dimerization emerged as the core driver of naive pluripotency with its levels diminished upon priming. Transient overexpression of the SK cocktail (Sox+Klf4) restored the dimerization and boosted the developmental potential of pluripotent stem cells across species, providing a universal method for naive reset in mammals.

Prenatal caffeine exposure induces autism-like behaviors in offspring under a high-fat diet via the gut microbiota-IL-17A-brain axis

Prenatal caffeine exposure (PCE) is a significant contributor to intrauterine growth retardation (IUGR) in offspring, which has been linked to an increased susceptibility to autism spectrum disorder (ASD) later in life. Additionally, a high-fat diet (HFD) has been shown to exacerbate ASD-like behaviors, but the underlying mechanisms remain unclear. In this study, we first noted in the rat model of IUGR induced by PCE that male PCE offspring exhibited typical ASD-like behaviors post-birth, in contrast to their female counterparts. The female PCE offspring demonstrated only reduced abilities in free exploration and spatial memory. Importantly, both male and female PCE offspring displayed ASD-like behaviors when exposed to HFD. We further observed that PCE + HFD offspring exhibited damaged intestinal mucus barriers and disturbed gut microbiota, resulting in an increased abundance of Escherichia coli (E. coli). The induced differentiation of colonic Th17 cells by E. coli led to an increased secretion of IL-17A, which entered the hippocampus through peripheral circulation and caused synaptic damage in hippocampal neurons, ultimately resulting in ASD development. Our strain transplantation experiment suggested that E. coli-mediated increase of IL-17A may be the core mechanism of ASD with a fetal origin. In conclusion, PCE and HFD are potential risk factors for ASD, and E. coli-mediated IL-17A may play a crucial role in fetal-originated ASD through the gut-brain axis.

Variant spectrum of F8 and F9 in hemophilia patients from southern China and 26 novel variants

Hemophilia, an X-linked recessive disorder, is characterized by spontaneous or trauma-induced prolonged bleeding. It is classified as hemophilia A when caused by variants in the F8 gene, and hemophilia B when caused by F9 variants. Few studies have described hemophilia variants in the Chinese population. This study aimed to investigate the clinical and genetic profiles of 193 hemophilia patients from southern China. Utilizing Sanger sequencing, multiplex ligation-dependent probe amplification, gap detection, long-range PCR, and multiplex PCR, we identified both F8 and F9 gene variants. Pregnant women with a history of hemophilia A offspring underwent amniocentesis or villus sampling for the variant detection. Variants in F8 and F9 were pinpointed in 183 patients, with 26 being novel discoveries. Notably, genetic testing was absent in the initial evaluation of 133 out of 161 patients, leading to a protracted average definitive diagnosis timeline of 2 years. Remarkably, two hemophilia A cases with anticipated severe phenotypes due to protein-truncating variants presented with only moderate or mild clinical manifestations. Among the 40 fetuses tested, 34 were males, with 17 exhibiting hemizygous variants in the F8 gene. Our results contribute to the broader understanding of F8 and F9 variant spectrum and highlight the underuse of genetic analyses in southern China.

Seasonal variation in air pollutant levels and its effects on the sex ratio at birth on Fukue island, Japan

BACKGROUND

In general, a slightly higher number of boys are born than girls, and the sex ratio at birth (number of male births/number of female births) is reported to be 1.03-1.07 in many countries. However, pregnant women exposed to high levels of atmospheric particulate matter have a reduced sex ratio at birth. Exposure to air pollutants can also lead to premature birth, suggesting that inflammation within the body may affect pregnancy maintenance and fetal development. On the other hand, the effects of air pollutants carried from afar by monsoons on the sex ratio at birth in downstream areas have not been evaluated. We focused on the Goto Islands, where various air pollutants flow from the Eurasian continent. The objective of this study was to clarify the effects of the atmospheric level of each pollutant on the sex ratio at birth on the Goto Islands.

METHODS

We extracted observation data of particulate matter 2.5, sulfur dioxide, oxidants, nonmethane hydrocarbons, and methane from the National Institute for Environmental Studies database. In addition, the monthly sex ratio at birth was calculated using birth data from the National Statistics Center. To evaluate the effect of substance exposure just before fertilization on the sex ratio at birth, we analyzed the relationship between the observed pollutant level and the sex ratio at birth 9 months later. A stepwise generalized linear model was used to analyze the effects of air pollutant levels on the sex ratio at birth.

RESULTS

The observed values for all pollutants were significantly different between seasons, including the particulate matter 2.5 (p < 0.0001), sulfur dioxide (p = 0.0026), oxidant (p < 0.0001), nonmethane hydrocarbon (p < 0.0001), and methane (p < 0.0001) values. In the target population in the target period, the total number of births was 1835, and the sex ratio at birth was 0.967. Univariate analysis showed that the values of particulate matter 2.5 (p = 0.0157) and oxidants (p = 0.0047) correlated negatively with the sex ratio at birth. In addition, the results of multivariate analysis using the stepwise method in the model equation indicated that every 1 ppm increase in the observed OX value resulted in a 0.311 decrease in the sex ratio at birth (p = 0.0034).

CONCLUSIONS

We evaluated the relationship between seasonal variations in air pollutant levels and the sex ratio at birth 9 months later on the Goto Islands. We found that an increase in oxidant levels just before and after conception may be a risk factor for a lower sex ratio at birth. Due to the previously reported vulnerability of male fetuses, females who become pregnant when air pollutant concentrations are high may be more likely to have a female baby. It is necessary to evaluate the effects of oxidants on various aspects of pregnancy and childbirth.

Fetal growth at term and placental oxidative stress in a tissue micro-array model: a histological and immunohistochemistry study

This study examines 8-hydroxyguanine (8-oxo-Gua) staining in placental tissue samples based on fetal size at birth as well as its relationships with placental histology and other pregnancy variables. This prospective cohort study included women > 18 years with a singleton pregnancy, a live fetus, fluency in Italian, and delivery at term. A total of 165 pregnancies were included in the study. The nuclear syncytiotrophoblast 8-oxo-Gua staining score in LGA was substantially greater than in late FGR (p < 0.05), although the cytoplasm score was lower in SGA and LGA than in AGA (p < 0.05). Furthermore, a sex-specific pattern of 8-oxo-Gua staining was discovered in single-term placentas, with more oxidative damage found in the nuclei of syncytiotrophoblast cells and stromal and endothelial cells in AGA males compared to AGA females (p < 0.05). Second, the histological pattern of late FGR placentae differed by gender. Finally, a significant correlation (p < 0.05) was found between high-intensity 8-oxo-Gua staining in the cytoplasm of syncytiotrophoblast cells and thrombi in the chorionic plate or villi in males. On the other hand, female fetuses demonstrated a significant connection (p < 0.05) between high-intensity 8-oxo-Gua staining in endothelial and stromal cells and high birthweight MoM values. Our findings indicated a significant variation in the oxidative stress pattern between male and female placentae, implying that fetal growth is regulated differently in the two sexes.

Factors affecting male-to-female ratio at birth in frozen-thawed embryo transfer cycles: a large retrospective cohort study

Background

ICSI (intracytoplasmic sperm injection) leads to a reduced male-to-female ratio at birth, whereas blastocyst transfer results in an increased male-to-female ratio. However, limited knowledge exists regarding the impact of these factors on the live birth rate for each gender. This study aimed to investigate the influence of patient characteristics and treatment parameters on the live birth rate for each gender, as well as the ultimate male-to-female ratio at birth in frozen-thawed embryo transfer (FET) cycles.

Method

This retrospective cohort study involved a total of 28,376 FET cycles and 9,217 subsequent deliveries, spanning from January 2003 to December 2015. The study consisted of two parts. First, logistic regression models were constructed to determine the factors influencing the male-to-female ratio among babies born after FET. Second, we aimed to investigate the mechanisms underlying this sex ratio imbalance by analyzing data from all transfer cycles. Generalized estimated equations were employed to assess the impact of risk factors on rates of male and female live births separately.

Results

ICSI resulted in a lower proportion of male offspring compared to in vitro fertilization (IVF) (50.1% vs. 53.7%, aOR: 0.87, 95% CI: 0.80-0.96). Conversely, blastocyst transfer yielded a higher proportion of male offspring than cleavage-stage embryo transfer (58.7% vs. 51.6%, aOR: 1.32, 95% CI: 1.17-1.48). Analysis of all cycles indicated that ICSI resulted in a reduced likelihood of male live birth in comparison to IVF (19.8% vs. 21.6%, aOR: 0.90, 95% CI: 0.83-0.97). However, the transfer of blastocysts rather than cleavage-stage embryos not only increased the chance of male live birth (26.9% vs. 20.2%, aOR: 1.70, 95% CI:1.56-1.85) but also facilitated female live birth (20.3% vs. 19.3%, aOR: 1.26, 95% CI: 1.15-1.39).

Conclusion

ICSI was associated with a reduction in the male-to-female sex ratio and a lower rate of male live births, while blastocyst transfer was associated with an increased male-to-female sex ratio at birth and a higher rate of male live births.

Sex differences in placenta-derived markers and later autistic traits in children

Autism is more prevalent in males and males on average score higher on measures of autistic traits. Placental function is affected significantly by the sex of the fetus. It is unclear if sex differences in placental function are associated with sex differences in the occurrence of autistic traits postnatally. To assess this, concentrations of angiogenesis-related markers, placental growth factor (PlGF) and soluble fms-like tyrosine kinase (sFlt-1) were assessed in maternal plasma of expectant women in the late 1^st (mean= 13.5 [SD = 2.0] weeks gestation) and 2^nd trimesters (mean=20.6 [SD = 1.2] weeks gestation), as part of the Generation R Study, Rotterdam, the Netherlands. Subsequent assessment of autistic traits in the offspring at age 6 was performed with the 18-item version of the Social Responsiveness Scale (SRS). Associations of placental protein concentrations with autistic traits were tested in sex-stratified and cohort-wide regression models. Cases with pregnancy complications or a later autism diagnosis (n = 64) were also assessed for differences in placenta-derived markers. sFlt-1 levels were significantly lower in males in both trimesters but showed no association with autistic traits. PlGF was significantly lower in male pregnancies in the 1^st trimester, and significantly higher in the 2^nd trimester, compared to female pregnancies. Higher PlGF levels in the 2^nd trimester and the rate of PlGF increase were both associated with the occurrence of higher autistic traits (PlGF-2^nd: n = 3469,b = 0.24 [SE = 0.11], p = 0.03) in both unadjusted and adjusted linear regression models that controlled for age, sex, placental weight and maternal characteristics. Mediation analyses showed that higher autistic traits in males compared to females were partly explained by higher PlGF or a faster rate of PlGF increase in the second trimester (PlGF-2^nd: n = 3469, ACME: b = 0.005, [SE = 0.002], p = 0.004). In conclusion, higher PlGF levels in the 2^nd trimester and a higher rate of PlGF increase are associated with both being male, and with a higher number of autistic traits in the general population.

Sex differences in the effects of prematurity and/or low birthweight on neurodevelopmental outcomes: systematic review and meta-analyses

BACKGROUND

Premature birth and/or low birthweight have long-lasting effects on cognition. The purpose of the present systematic review is to examine whether the effects of prematurity and/or low birth weight on neurodevelopmental outcomes differ between males and females.

METHODS

Web of Science, Scopus, and Ovid MEDLINE were searched for studies of humans born premature and/or of low birthweight, where neurodevelopmental phenotypes were measured at 1 year of age or older. Studies must have reported outcomes in such a way that it was possible to assess whether effects were greater in one sex than the other. Risk of bias was assessed using both the Newcastle-Ottawa scale and the National Institutes of Health Quality assessment tool for observational cohort and cross-sectional studies.

RESULTS

Seventy-five studies were included for descriptive synthesis, although only 24 presented data in a way that could be extracted for meta-analyses. Meta-analyses found that severe and moderate prematurity/low birthweight impaired cognitive function, and severe prematurity/low birthweight also increased internalizing problem scores. Moderate, but not severe, prematurity/low birthweight significantly increased externalizing problem scores. In no case did effects of prematurity/low birthweight differ between males and females. Heterogeneity among studies was generally high and significant, although age at assessment was not a significant moderator of effect. Descriptive synthesis did not identify an obvious excess or deficiency of male-biased or female-biased effects for any trait category. Individual study quality was generally good, and we found no evidence of publication bias.

CONCLUSIONS

We found no evidence that the sexes differ in their susceptibility to the effects of severe or moderate prematurity/low birthweight on cognitive function, internalizing traits or externalizing traits. Result heterogeneity tended to be high, but this reflects that one sex is not consistently more affected than the other. Frequently stated generalizations that one sex is more susceptible to prenatal adversity should be re-evaluated.

Pregnancy bias toward boys or girls: The Japan Environment and Children's Study

The sex of the conceived child is a significant concern for parents. To verify whether there women have pregnancy bias toward boys or girls, we investigated whether the history of continuous same-sex pregnancy was associated with the subsequent child's sex. We prospectively analyzed data from the Japan Environment and Children's Study, a birth cohort study. We included all cases of singleton live births (n = 98 412). Women with pregnancy due to infertility treatment were excluded (n = 6255); Similarly, women with a history of miscarriage, artificial abortion, stillbirth, and multiple pregnancies, and those with missing data on the sex of the previous child were excluded. Altogether, 62 718 women were included. For the first live birth, a male-biased sex ratio of 1.055 was observed. Further, no significant difference was found in the sex ratio of the conceived child between women with one boy and those with one girl previously. However, when there were more than two children previously, the subsequently conceived child's male/female sex ratio was significantly higher among boy-only mothers than among girl-only mothers. The results indicated that several pregnant women are biased toward conceiving either boys or girls.

Sex as a Factor in Murine Radiation Research: Implications for Countermeasure Development

There is an increased threat of exposure to ionizing radiation; in the event of such exposure, the availability of medical countermeasures will be vital to ensure the protection of the population. Effective countermeasures should be efficacious across a varied population and most importantly amongst both males and females. Radiation research must be conducted in animal models which act as a surrogate for the human response. Here, we identify differences in survival in male and female C57BL/6 in both a total body irradiation (TBI) model using the Armed Forces Radiobiology Research Institute (AFRRI) 60Co source and a partial body irradiation (PBI) model using the AFRRI Linear Accelerator (LINAC) with 4 MV photons and 2.5% bone marrow shielding. In both models, we observed a higher degree of radioresistance in female animals and a corresponding radiosensitivity in males. One striking difference in male and female rodents is body size/weight and we investigated the role of pre-irradiation body weight on survivability for animals irradiated at the same dose of irradiation (8 Gy TBI, 14 Gy PBI). We found that weight does not influence survival in the TBI model and that heavier males but lighter females have increased survival in the PBI model. This incongruence in survival amongst the sexes should be taken into consideration in the course of developing radiation countermeasures for response to a mass casualty incident.

Chromosomal abnormalities in recurrent pregnancy loss and its association with clinical characteristics

OBJECTIVE

To evaluate the distribution of chromosomal abnormalities in a recurrent pregnancy loss (RPL) cohort and explore the associations between chromosomal abnormalities and clinical characteristics.

METHOD

Over a 5-year period, fresh products of conception (POC) from women with RPL were analyzed by single-nucleotide polymorphism (SNP) array at our hospital. After obtaining the information on clinical characteristics, we investigated the associations between the causative chromosomal abnormalities and clinical characteristics by the chi-squared test or Fisher's exact test and logistic regression.

RESULTS

A total of 2383 cases were enrolled. Overall, 56.9% (1355/2383) were identified with causative chromosomal abnormalities, of which 92.1% (1248/1355) were numerical abnormalities, 7.5% (102/1355) were structural variants, and 0.4% (5/1355) were loss of heterozygosity (LOH). The risk of numerical abnormalities was increased in women with maternal age ≥ 35 years (OR, 1.71; 95% CI, 1.41-2.07), gestational age at pregnancy loss ≤ 12 weeks (OR, 2.78; 95% CI, 1.79-4.33), less number of previous pregnancy losses (twice: OR, 2.32; 95% CI, 1.84-2.94; 3 times: OR, 1.59; 95% CI, 1.23-2.05, respectively), and pregnancy with a female fetus (OR, 1.37; 95% CI, 1.15-1.62). The OR of pregnancy loss with recurrent abnormal CMA was 4.00 (95% CI: 1.87-8.58, P < 0.001) and the adjusted OR was 5.05 (95% CI: 2.00-12.72, P = 0.001). However, the mode of conception was not associated with the incidence of numerical abnormality. No association was noted between structural variants and clinical characteristics.

CONCLUSION

Chromosomal abnormality was the leading cause of RPL. Numerical chromosome abnormality was more likely to occur in cases with advanced maternal age, an earlier gestational age, fewer previous pregnancy losses, and pregnancy with a female fetus.

The Role of Maternal Preconception Adiposity in Human Offspring Sex and Sex Ratio

We evaluated relationships between preconception adiposity and human offspring sex and sex ratio. Using data from a prospective preconception cohort nested within a randomized controlled trial based at 4 US clinical sites (2006-2012), we used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for male:female sex ratio, and log-identity regression to estimate risk differences (RDs) and 95% CIs for male and female livebirth according to preconception adiposity measures. Inverse-probability weights accounted for potential selection bias. Among 603 women attempting pregnancy, there were meaningful reductions in sex ratio for the highest category of each adiposity measure. The lowest sex ratios were observed for obesity (body mass index of ≥30, calculated as weight (kg)/height (m)2, OR = 0.48, 95% CI: 0.26, 0.88) relative to normal body mass index, and the top tertiles (tertile 3) of serum leptin (OR = 0.50, 95% CI: 0.32, 0.80) and skinfold measurements (OR = 0.50, 95% CI: 0.32, 0.79) relative to the lowest tertiles. Reductions were driven by 11-15 fewer male livebirths per 100 women (for obesity, RD = -15, 95% CI: -23, -6.7; for leptin tertile 3, RD = -11, 95% CI: -20, -3.2; and for skinfolds tertile 3, RD = -11, 95% CI: -19, -3.3). We found that relationships between preconception adiposity measures and reduced sex ratio were driven by a reduction in male births.

Sex roles and sex ratios in animals

In species with separate sexes, females and males often differ in their morphology, physiology and behaviour. Such sex-specific traits are functionally linked to variation in reproductive competition, mate choice and parental care, which have all been linked to sex roles. At the 150th anniversary of Darwin's theory on sexual selection, the question of why patterns of sex roles vary within and across species remains a key topic in behavioural and evolutionary ecology. New theoretical, experimental and comparative evidence suggests that variation in the adult sex ratio (ASR) is a key driver of variation in sex roles. Here, we first define and discuss the historical emergence of the sex role concept, including recent criticisms and rebuttals. Second, we review the various sex ratios with a focus on ASR, and explore its theoretical links to sex roles. Third, we explore the causes, and especially the consequences, of biased ASRs, focusing on the results of correlational and experimental studies of the effect of ASR variation on mate choice, sexual conflict, parental care and mating systems, social behaviour, hormone physiology and fitness. We present evidence that animals in diverse societies are sensitive to variation in local ASR, even on short timescales, and propose explanations for conflicting results. We conclude with an overview of open questions in this field integrating demography, life history and behaviour.

Infant sex at birth and long-term maternal mortality

BACKGROUND

Maternal adaptations may vary by foetal sex. Whether male infants influence long-term mortality in mothers remains uncertain.

OBJECTIVE

The objective of the study was to examine whether male infants increase the risk of maternal mortality.

METHODS

This study included pregnant women enrolled at 12 US sites from 1959 to 1966 in the Collaborative Perinatal Project (CPP). Collaborative Perinatal Project records were linked to the National Death Index and the Social Security Master Death File to ascertain deaths until 2016. Foetal sex was determined by infant sex at birth, defined as the total number of male or female infants in pregnancies prior to or during enrolment in the CPP. In secondary analyses, exposure was defined as infant sex at the last CPP delivery. Outcomes included all-cause and underlying causes of mortality. We used Cox proportional hazards models weighted by the number of prior live births and stratified our models by parity and race/ethnicity.

RESULTS

Among 48,188 women, 50.8% had a male infant at their last registered CPP pregnancy and 39.0% had a recorded death after a mean follow-up of 47.8 years (SD 10.5 years). No linear association was found between the number of liveborn males and all-cause mortality (primipara women: HR 1.02, 95% CI 0.95, 1.09, multipara women, 1 prior live birth: HR 0.96, 95% CI 0.89, 1.03, multipara women, ≥2 prior live births: HR 0.97, 95% CI 0.85, 1.11). A similar trend was noted for cardiovascular- and cancer-related mortality. At the last delivery, women with a male infant did not have an increased risk of all-cause or cause-specific mortality compared to women with a female infant. These findings were consistent across racial/ethnic groups.

CONCLUSIONS

Women who give birth to male infants, regardless of number, are not at increased risk of all-cause and cause-specific mortality. These findings suggest that giving birth to male infants may not independently influence the long-term health of women.

Comparative cytogenetics of anembryonic pregnancies and missed abortions in human

Miscarriage is an important problem in human reproduction, affecting 10-15 % of clinically recognized pregnancies. The cases of embryonic death can be divided into missed abortion (MA), for which the ultrasound sign of the embryo death is the absence of cardiac activity, and anembryonic pregnancy (AP) without an embryo in the gestational sac. The aim of this study was to compare the frequency of chromosomal abnormalities in extraembryonic tissues detected by conventional cytogenetic analysis of spontaneous abortions depending on the presence or absence of an embryo. This is a retrospective study of 1551 spontaneous abortions analyzed using GTG-banding from 1990 to 2022 (266 cases of AP and 1285 cases of MA). A comparative analysis of the frequency of chromosomal abnormalities and the distribution of karyotype frequencies depending on the presence of an embryo in the gestational sac was carried out. Statistical analysis was performed using a chi-square test with a p <0.05 significance level. The total frequency of chromosomal abnormalities in the study was 53.6 % (832/1551). The proportion of abnormal karyotypes in the AP and MA groups did not differ significantly and amounted to 57.1 % (152/266) and 52.9 % (680/1285) for AP and MA, respectively (p = 0.209). Sex chromosome aneuploidies and triploidies were significantly less common in the AP group than in the MA group (2.3 % (6/266) vs 6.8 % (88/1285), p = 0.005 and 4.9 % (13/266) vs 8.9 % (114/1285), p = 0.031, respectively). Tetraploidies were registered more frequently in AP compared to MA (12.4 % (33/266) vs. 8.2 % (106/1285), p = 0.031). The sex ratio among abortions with a normal karyotype was 0.54 and 0.74 for AP and MA, respectively. Thus, although the frequencies of some types of chromosomal pathology differ between AP and MA, the total frequency of chromosomal abnormalities in AP is not increased compared to MA, which indicates the need to search for the causes of AP at other levels of the genome organization, including microstructural chromosomal rearrangements, monogenic mutations, imprinting disorders, and epigenetic abnormalities.

Severe cyclones and sex-specific birth outcomes in Queensland, Australia: An interrupted time-series analysis

OBJECTIVES

A male is less adaptable to biological stressors than a female fetus with consequent higher morbidity and mortality. Adverse birth outcomes increase and male livebirths decrease after environmental disasters, economic crises, and terrorist events. We hypothesized the ratio of male to female livebirths would decrease in areas affected by severe tropical cyclones (TCs) in Queensland, Australia. Additionally, in male livebirths, there would be an increase in preterm and low birthweight births. Lastly, we hypothesized that the pregnancy stage at which exposure occurred would modify the association between TC exposure and observed outcomes.

METHODS

Interrupted time series analysis was used to analyze Queensland administrative birth records from July 2007 to June 2018 for significant changes in the sex ratio at birth, measured as the proportion of male livebirths. Adjusted generalized linear models were fitted to births in areas affected by two category five TCs: cyclones Yasi (February 2011) and Marcia (February 2015). To explore male mortality and morbidity risk, additional analysis was conducted on the proportion of male stillborn, low birthweight, and preterm births. The association between estimated pregnancy stage during the TC and the proportion of male births was also analyzed.

RESULTS

Contrary to our hypothesis, increases in the proportion of male livebirths were observed following early-pregnancy exposure to cyclone Yasi and mid-pregnancy exposure to Marcia, although the latter was not statistically significant. No significant changes were observed in proportions of male stillborn, low birthweight, and preterm births.

CONCLUSIONS

This study found a significant association between severe TCs and sex ratio at birth. The stage of pregnancy at which maternal stressors were experienced modified this association. Among people exposed in early to mid-pregnancy, the proportion of male births was higher. This may be because of differential loss of females in utero. Studying sex differences in birth outcomes provides insight into in utero vulnerabilities associated with environmental stressors. Climate change is increasing the intensity and frequency of natural disasters. Understanding fetal vulnerability to environmental stressors will provide crucial information supporting early life health interventions that mitigate the immediate and long-term effects.

Gender bias in fetal malformations: A cross-sectional study in Asian populations

OBJECTIVES

The aim of this study was to detect any gender bias in fetal malformation cases.

DESIGN

This study was a cross-sectional, quantitative survey.

SUBJECTS

Overall, 1,661 Asian fetal malformation cases involving induced abortions in the obstetrics department of the first Affiliated Hospital of Zhengzhou University from 2012 to 2021 were included.

MAIN OUTCOME MEASURES

Measurements of ultrasound detectable structural malformations were classified into 13 subtypes. Karyotyping, single nucleotide polymorphism (SNP) array, or sequencing diagnosis of these fetus was also included in the outcome measures.

RESULTS

The sex ratio (male/female) of all malformation types was 1.446. Cardiopulmonary had the highest proportion of all malformation types with 28%. Diaphragmatic hernia, omphalocele, gastroschisis, nuchal translucency (NT), and Multy malformations had significantly higher proportions of males (p < 0.05). Digestive system malformations had a significantly higher proportion of females (p < 0.05). Maternal age was associated with genetic factors (r = 0.953, p < 0.001) and inversely associated with brain malformations (r = -0.570, p = 0.002). More males were found with trisomy 21, trisomy 18, and monogenetic diseases, while duplications, deletions, and uniparental disomy (UPD) had similar sex ratios between males and females, but not statistically significant.

CONCLUSION

Sex differences are common with fetal malformations, with higher proportions of males. Genetic testing has been proposed to account for these differences.

Epidemiologic and clinical characteristics of selected congenital anomalies at the largest Bosnian pediatric surgery tertiary center

Congenital anomalies (CA) are any abnormality present at birth, either structural or functional, that may potentially affect an infant's health, development, and/or survival. There is a paucity of studies on clinical characteristics and outcomes of CA in Bosnia and Herzegovina, mainly due to the lack of a nationwide congenital malformations monitoring system. A 5-year hospital-based study was conducted to determine the prevalence at birth and clinical characteristics of selected major CA in Sarajevo Canton, Bosnia and Herzegovina. Ninety-one CA were observed from 2012 to 2016 (the overall prevalence was 39.6 cases/10,000 live births). The mean age of neonates at diagnosis was 3 days. The gastrointestinal tract was the most commonly affected system (76.9%), with esophageal atresia (EA) being the most frequent (17.6% of all CA). Major CA were more prevalent among preterm infants than term infants (P = .001), particularly in males (61.5% vs. 38.5%; P = .028; M:F ratio was 1.59). Multiple CA were seen in 37.4% of neonates. The overall mortality rate of neonates was 11%, and the median length of hospital stay was 19.8 days. Our study revealed the distribution and clinical patterns of common major CA in the largest tertiary care facility in Bosnia and Herzegovina. It also confirmed a relatively high mortality rate, which requires further efforts to improve the quality of neonatal care in the country.

Ghosts, Divination, and Magic among the Nuosu: An Ethnographic Examination from Cognitive and Cultural Evolutionary Perspectives

I present a detailed ethnographic study of magic and divination of the Nuosu people in southwest China and offer a cognitive account of the surprising prevalence of these objectively ineffective practices in a society that has ample access to modern technology and mainstream Han culture. I argue that in the belief system of the Nuosu, ghosts, divination, and magical healing rituals form a closely interconnected web that gives sense and meaning to otherwise puzzling practices, and such a belief system is importantly supported and reinforced by individual's everyday experiences. Contemporary Nuosu people overwhelmingly treat these practices as instruments for achieving specific ends and often entertain considerable uncertainty regarding their efficacy, which may be overestimated for a number of reasons, including the following: (1) the intuitive plausibility of divination for ghost identification and exorcist rituals is enhanced by the belief in the existence of ghosts as a result of abductive reasoning, (2) negative instances (divinatory or healing ritual failures) are underreported, and (3) people's misperception of the probability of uncertain events' occurrence often prevents them from realizing that the efficacies of magical/divinatory practices do not outperform chance. I conclude with some comments on the generalizability of the psychological and social mechanisms discussed.

The Male to Female Ratio in Treatment-Warranted Retinopathy of Prematurity: A Systematic Review and Meta-analysis

Importance

Literature and anecdotal evidence suggest a relationship between male sex and retinopathy of prematurity (ROP). It is not known whether a difference, if present, is sex-related pathophysiologic predisposition or sex difference in meeting ROP screening criteria.

Objective

To evaluate the association of sex with the development of treatment-warranted ROP.

Data Sources

PubMed, Embase, and Web of Science databases were searched from 2000 to 2022. The search strategy used keywords including retinopathy of prematurity or ROP or retrolental fibroplasia and treatment or anti-VEGF or bevacizumab or ranibizumab or aflibercept or conbercept or laser or cryotherapy and gender or sex or male or female and medical subject headings terms.

Study Selection

All studies reporting on treatment with anti-vascular endothelial growth factor, laser photocoagulation, and/or cryotherapy for ROP were identified. Studies reporting sex distribution in the treatment group were included in the meta-analysis. Exclusion criteria included case reports, case series of fewer than 10 treated patients, systematic reviews, conference abstracts, letters to the editor, animal studies, and non-English records.

Data Extraction and Synthesis

Two reviewers independently screened and extracted the data following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The proportions of treated male and female infants were combined using random-effects meta-analysis.

Main Outcomes and Measures

Numbers and percentages of male and female infants treated for ROP.

Results

Of 11 368 identified studies, 316 met inclusion criteria, yielding a total of 31 026 treated patients. A higher percentage of male infants were treated for ROP (55% [95% CI, 0.54%-0.55%]), with low heterogeneity between studies (I2 = 34%; P < .001). Thirty-eight studies reported sex distribution in the screened population (170 053 patients; 92 612 [53%] male vs 77 441 [47%] female). There was no significant difference in the odds of receiving treatment between screened male and female infants (pooled odds ratio, 1.04 [95% CI, 0.91-1.18]; P = .67).

Conclusions and Relevance

More male infants are treated for ROP than female infants. This could be due to a known relative pathophysiological fragility of preterm male infants in addition to a difference in ROP screening rates, with more male infants meeting the criteria than female infants. These findings have implications for future studies and may prompt more careful clinical monitoring of male neonates.

Some Aspects of Women’s Health in Republic of Macedonia

INTRODUCTION: Sex and gender "matters" in terms of the health status as well as a result of both biological and gender-related differences. AIM: To analyze sex and gender-based differences in North Macedonia through analysis of some aspects of mortality, the knowledge and attitudes related to women’s health. METHODS: Analysis of the general and age-standardized mortality patterns and CAPI (Computer-assisted personal interview) composed on different topics including women's health for the period 2017-2020 were used. RESULTS: Age-standardized mortality rates (all-causes of death, circulatory and respiratory diseases and neoplasms) are prevalent and higher in the male population in North Macedonia. A significantly higher all-cause mortality trend for both sexes was found in 2020 making this year hardly comparable with the previous years. A decreasing trend of malignant neoplasms rate of female genital organs and an increasing trend of breast cancer mortality is observed. The majority of the respondents (50.6%) rated their current health status as excellent with a statistically significant difference between the age and ethnical groups. One-third of the respondents reported regular physical activity, mostly on a daily basis. The majority (39.3%) are overweight and 27.5% belongs to the obesity class I without a significant difference in terms of ethnicity. Respondents (27%), reported that have high blood pressure, 20.2% vaginal infections, 19.9% allergies, heart issues 15.1%, anemia 11.7%, while diabetes and cancer 8.5% and 2.5% respectively. The youngest and oldest age group of Albanian women are the least informed about the early detection procedures of malignant compared to Macedonian women and other ethnic groups. CONCLUSIONS: Analyzing some aspects of women's health in North Macedonia through the mortality, knowledge and attitudes of Macedonian women, we provide some further evidence for the development and implementation of targeted interventions and policies aimed to reduce the sex and gender-based health inequalities in the country.

Pandemic influenza and gender imbalance: Mortality selection before births

This study uses data from the 1918-1920 influenza pandemic in Japan along with newly digitized and complete census records on births and infant deaths to analyze mortality selection in utero. I find that fetal exposure to the influenza pandemic during the first trimester of the pregnancy decreases the proportion of males at birth. The results from mechanism analysis suggest that this decline in male births is associated with the deterioration of fetal and infant health. This result supports a wide range of existing literature on the long-run adverse effects of pandemic influenza.

First Trimester of Pregnancy as the Sensitive Period for the Association between Prenatal Mosquito Coil Smoke Exposure and Preterm Birth

Mosquito coils are efficient mosquito repellents and mosquito coil smoke (MCS) contributes to indoor air pollution. However, no prior population-based study has investigated whether prenatal MCS exposure is a risk factor for preterm birth (PTB) and whether exposure to MCS in different trimesters of pregnancy is associated with different levels of risk. The sample involved 66,503 mother-child dyads. Logistic regression models were used to examine the relationships between prenatal MCS exposure during different trimesters of pregnancy and PTB. We found that prenatal MCS exposure was associated with a greater likelihood of PTB (OR = 1.12, 95%CI: 1.05-1.20). The prenatal MCS exposure during the first trimester was associated with 1.17 (95%CI: 1.09-1.25) times the odds of being PTB, which was higher than exposure during the second trimester (OR = 1.11, 95%CI: 1.03-1.19) and during the third trimester (OR = 1.08, 95%CI: 1.01-1.16). In the stratified analysis, prenatal MCS exposure significantly increased PTB risk among girls but not among boys. Our results indicated that maternal MCS exposure during pregnancy was associated with PTB and that the first trimester might be the sensitive period. In light of these findings, public health interventions are needed to reduce prenatal exposure to MCS, particularly during the first trimester of pregnancy.

Differential expression of placental 11β-HSD2 induced by high maternal glucocorticoid exposure mediates sex differences in placental and fetal development

A variety of adverse environmental factors during pregnancy cause maternal chronic stress. Caffeine is a common stressor, and its consumption during pregnancy is widespread. Our previous study showed that prenatal caffeine exposure (PCE) increased maternal blood glucocorticoid levels and caused abnormal development of offspring. However, the placental mechanism for fetal development inhibition caused by PCE-induced high maternal glucocorticoid has not been reported. This study investigated the effects of PCE-induced high maternal glucocorticoid level on placental and fetal development by regulating placental 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) expression and its underlying mechanism. First, human placenta and umbilical cord blood samples were collected from women without prenatal use of synthetic glucocorticoids. We found that placental 11β-HSD2 expression was significantly correlated with umbilical cord blood cortisol level and birth weight in male newborns but not in females. Furthermore, we established a rat model of high maternal glucocorticoids induced by PCE (caffeine, 60 mg/kg·d, ig), and found that the expression of 11β-HSD2 in male PCE placenta was decreased and negatively correlated with the maternal/fetal/placental corticosterone levels. Meanwhile, we found abnormal placental structure and nutrient transporter expression. In vitro, BeWo cells were used and confirm that 11β-HSD2 mediated inhibition of placental nutrient transporter expression induced by high levels of glucocorticoid. Finally, combined with the animal and cell experiments, we further confirmed that high maternal glucocorticoid could activate the GR-C/EBPα-Egr1 signaling pathway, leading to decreased expression of 11β-HSD2 in males. However, there was no significant inhibition of placental 11β-HSD2 expression, placental and fetal development in females. In summary, we confirmed that high maternal glucocorticoids could regulate placental 11β-HSD2 expression in a sex-specific manner, leading to differences in placental and fetal development. This study provides the theoretical and experimental basis for analyzing the inhibition of fetoplacental development and its sex difference caused by maternal stress.

Skewed X-Chromosome Inactivation as a Possible Marker of X-Linked CNV in Women with Pregnancy Loss

Skewed X-chromosome inactivation (sXCI) can be a marker of lethal genetic variants on the X chromosome in a woman since sXCI modifies the pathological phenotype. The aim of this study was to search for CNVs in women with miscarriages and sXCI. XCI was assayed using the classical method based on the amplification of highly polymorphic exon 1 of the androgen receptor (AR) gene. The XCI status was analysed in 313 women with pregnancy loss and in 87 spontaneously aborted embryos with 46,XX karyotype, as well as in control groups of 135 women without pregnancy loss and 64 embryos with 46,XX karyotype from induced abortions in women who terminated a normal pregnancy. The frequency of sXCI differed significantly between women with miscarriages and women without pregnancy losses (6.3% and 2.2%, respectively; p = 0.019). To exclude primary causes of sXCI, sequencing of the XIST and XACT genes was performed. The XIST and XACT gene sequencing revealed no known pathogenic variants that could lead to sXCI. Molecular karyotyping was performed using aCGH, followed by verification of X-linked CNVs by RT-PCR and MLPA. Microdeletions at Xp11.23 and Xq24 as well as gains of Xq28 were detected in women with sXCI and pregnancy loss.

Are there sex differences in fetal growth strategies and in the long-term effects of pregnancy complications on cognitive functioning?

Males and females have been proposed to have different prenatal growth strategies, whereby males invest more in fetal growth and less in placental development, leaving them more susceptible to early-life adversity. We tested predictions of this hypothesis using data from the National Collaborative Perinatal Project. Male newborns were heavier than females, but there was no difference in placental weight, adjusting for birthweight. Among infants born prior to 33 weeks, the difference in birthweight between males and females was greater among those who did not survive than among those who did, potentially reflecting a strategy whereby males maintained growth in the face of prenatal insults, while females adjusted growth. However, there was no significant difference in mortality between the sexes. Being born small-for-gestational age or very preterm (prior to 33 weeks) was associated with significantly reduced performance for most of the cognitive traits examined at 7 years, although maternal preeclampsia was associated with reduced performance in fewer traits. Generally, these effects of early-life adversity (poor fetal growth, prematurity, and preeclampsia) did not differ between the sexes. However, analyzing the sexes separately (rather than testing the interaction between sex and adversity) resulted in numerous spurious sex-specific effects, whereby the effect of early-life adversity appeared to be significant in one sex but not the other. Overall, we found little support for the hypothesis that males prioritize growth more than females, and that this makes them more susceptible to early-life adversity. Furthermore, our results show that analyzing the sexes separately, rather than testing the adversity by sex interaction, can be highly misleading.

The association between the 2D:4D ratio and offspring sex at birth: A cross-sectional study in Ghana

OBJECTIVES

The 2D:4D ratio is the putative marker of prenatal androgen exposure. Low maternal 2D:4D ratio has been associated with high or male-biased secondary sex ratio. Hitherto, there has not been any study in Ghana regarding the maternal 2D:4D ratio and sex ratio at birth. This study sought to investigate this observation in a Ghanaian population.

METHOD

The study was cross-sectional from December 2020 to April 2021 involving 272 first-time mothers. The mean ± SD age of the mothers was 23.9 ± 3.67 years. The right (2D:4DR), the left (2D:4DL), the mean (M2D:4D) digit ratios and the right-left difference (Dr-l) of the mothers were measured using computer-assisted analysis. The mothers were stratified by their digit ratios, and the cohort sex ratio (CSR) for each stratum was then calculated as the proportion of sons.

RESULTS

The mean ± SD of the 2D:4DR of mothers-with-daughters and mothers-with-sons were 0.941 ± 0.032 and 0.933 ± 0.037, respectively. The mean ± SD of the 2D:4DL of mothers-with-daughters was 0.934 ± 0.034, while that of mothers-with-sons was 0.931 ± 0.039. The offspring sex at birth and the CSR was not associated with either the mother's right, left, mean 2D:4D ratio or their difference (Dr-l). However, mothers-with-daughters showed rightward asymmetry in their 2D:4D ratios as the Dr-l significantly and positively deviated from zero (p < .010).

CONCLUSION

The maternal 2D:4D ratio may not be associated with their offspring sex at birth among first-time mothers. This study adds to the limited data on studies regarding offspring sex at birth and the 2D:4D ratio in Ghana and Sub-Saharan Africa.

X Chromosome Inactivation Timing is Not eXACT: Implications for Autism Spectrum Disorders

The etiology of autism spectrum disorders (ASD) is complex, involving different combinations of genetic and environmental factors. My lab's approach has been to investigate DNA methylation as a tractable genome-wide modification at the interface of these complex interactions, reflecting past and future events in the molecular pathogenesis of ASD. Since X-linked genes were enriched in DNA methylation differences discovered from cord blood from newborns later diagnosed with ASD, this has prompted me to review and revisit the recent advancements in the field of X chromosome inactivation (XCI), particularly in humans and other primates. In this Perspective, I compare XCI mechanisms in different mammalian species, including the finding of the noncoding transcript XACT associated with X chromosome erosion in human pluripotent stem cells and recent findings from non-human primate post-implantation embryos. I focus on the experimentally challenging peri- and post-implantation stages of human development when the timing of XCI is prolonged and imprecise in humans. Collectively, this research has raised some important unanswered questions involving biased sex ratios in human births and the male bias in the incidence of ASD.

Placental energy metabolism in health and disease-significance of development and implications for preeclampsia

The placenta is a highly metabolically active organ fulfilling the bioenergetic and biosynthetic needs to support its own rapid growth and that of the fetus. Placental metabolic dysfunction is a common occurrence in preeclampsia although its causal relationship to the pathophysiology is unclear. At the outset, this may simply be seen as an "engine out of fuel." However, placental metabolism plays a vital role beyond energy production and is linked to physiological and developmental processes. In this review, we discuss the metabolic basis for placental dysfunction and propose that the alterations in energy metabolism may explain many of the placental phenotypes of preeclampsia such as reduced placental and fetal growth, redox imbalance, oxidative stress, altered epigenetic and gene expression profiles, and the functional consequences of these aberrations. We propose that placental metabolic reprogramming reflects the dynamic physiological state allowing the tissue to adapt to developmental changes and respond to preeclampsia stress, whereas the inability to reprogram placental metabolism may result in severe preeclampsia phenotypes. Finally, we discuss common tested and novel therapeutic strategies for treating placental dysfunction in preeclampsia and their impact on placental energy metabolism as possible explanations into their potential benefits or harm.

Extraordinarily precise nematode sex ratios: adaptive responses to vanishingly rare mating opportunities

Sex ratio theory predicts both mean sex ratio and variance under a range of population structures. Here, we compare two genera of phoretic nematodes (Parasitodiplogaster and Ficophagus spp.) associated with 12 fig pollinating wasp species in Panama. The host wasps exhibit classic local mate competition: only inseminated females disperse from natal figs, and their offspring form mating pools that consist of scores of the adult offspring contributed by one or a few foundress mothers. By contrast, in both nematode genera, only sexually undifferentiated juveniles disperse and their mating pools routinely consist of 10 or fewer adults. Across all mating pool sizes, the sex ratios observed in both nematode genera are consistently female-biased (approx. 0.34 males), but markedly less female-biased than is often observed in the host wasps (approx. 0.10 males). In further contrast with their hosts, variances in nematode sex ratios are also consistently precise (significantly less than binomial). The constraints associated with predictably small mating pools within highly subdivided populations appear to select for precise sex ratios that contribute both to the reproductive success of individual nematodes, and to the evolutionary persistence of nematode species. We suggest that some form of environmental sex determination underlies these precise sex ratios.

Girls start life on an uneven playing field

Background and objectives

Evolutionary research on the sex ratio at birth (SRB) has focused on explaining variability within and between populations, and whether parental fitness is maximized by producing daughters or sons. We tested predictors of SRB in a low-income setting, to understand whether girls differ from boys in their likelihood of being born into families with the capacity to invest in them, which has implications for their future health and fitness.

Methodology

We used data from a cluster randomized control trial from lowland rural Nepal (16 115 mother-child dyads). We applied principal component analysis to extract two composite indices reflecting maternal socio-economic and reproductive (parity, age) capital. We fitted mixed-effects logistic regression models to estimate odds ratios of having a girl in association with these individual factors and indices.

Results

The SRB was 112. Compared to the global reference SRB (105), there were seven missing girls per 100 boys. Uneducated, early-marrying, poorer and shorter mothers were more likely to give birth to girls. Analysing composite maternal indices, lower socio-economic and reproductive capital were independently associated with a greater likelihood of having a girl.

Conclusions and implications

In this population, girls start life facing composite disadvantages, being more likely than boys to be born to mothers with lower socio-economic status and reproductive capital. Both physiological and behavioural mechanisms may contribute to these epidemiological associations. Differential early exposure by sex to maternal factors may underpin intergenerational cycles of gender inequality, mediated by developmental trajectory, education and socio-economic status.

Blastocyst quality and perinatal outcomes of frozen-thawed single blastocyst transfer cycles

OBJECTIVE

To investigate the effects of blastocyst quality and morphological grade on the perinatal outcomes in patients undergoing frozen-thawed single blastocyst transfer cycles.

METHODS

This single-center retrospective cohort study included 2648 singleton neonates resulting from frozen-thawed single blastocyst transfers performed between January 2017 and September 2021. Multivariate logistic regression was performed to evaluate perinatal outcomes for their association with blastocyst quality and morphological parameters.

RESULT

Transfer of a good-quality blastocyst in a frozen-thawed cycle was associated with a lower rate of preterm delivery (PTD, adjusted OR =0.7, 95% CI 0.5-0.9; P=0.020) and a higher likelihood of a male neonate (adjusted OR =1.2, 95%CI 1.0-1.5; P=0.048). Compared with grade C inner cell mass (ICM) blastocyst transfer, grade B ICM (adjusted OR =0.5, 95%CI 0.2-0.9; P=0.027) and grade A ICM (adjusted OR =0.6, 95%CI 0.3-1.5; P=0.290) blastocyst transfers were associated with a lower rate of PTD, which was more evident for grade B ICM. After adjusting for confounders, the likelihood of a male neonate (grade B TE, OR =1.2, 95%CI 1.0-1.5, P=0.037; grade A TE OR =1.9, 95%CI 1.3-28, P=0.002) increased with increasing trophectoderm (TE) quality. Compared with expansion stage 4, the likelihood of a male neonate was 1.5 times greater with transfer of a stage 6 blastocyst (OR =1.5, 95%CI 1.0-2.3; P=0.06), and the risk of small for gestational age (SGA) was greater with transfer of a stage 5 blastocyst (adjusted OR =3.5, 95%CI 1.5-8.0; P=0.004). The overall grading of the blastocyst, expansion stage, ICM grade, and TE grade were not associated with length at birth, birthweight, large for gestational age (LGA), or birth defects (all P>0.05).

CONCLUSIONS

In frozen-thawed single blastocyst transfer cycles, transfer of a good-quality blastocyst was associated with a lower rate of PTD and a greater likelihood of a male neonate. Transfer of grade B ICM blastocysts decreased the rate of PTD, and TE quality was positively correlated with the likelihood of a male neonate.

Twinning during the pandemic: Evidence of selection in utero

Background and objectives

The suspicion that a population stressor as profound as the COVID-19 pandemic would increase preterm birth among cohorts in gestation at its outset has not been supported by data collected in 2020. An evolutionary perspective on this circumstance suggests that natural selection in utero, induced by the onset of the pandemic, caused pregnancies that would otherwise have produced a preterm birth to end early in gestation as spontaneous abortions. We test this possibility using the odds of a live-born twin among male births in Norway as an indicator of the depth of selection in birth cohorts.

Methodology

We apply Box–Jenkins methods to 50 pre-pandemic months to estimate counterfactuals for the nine birth cohorts in gestation in March 2020 when the first deaths attributable to SARS-CoV-2 infection occurred in Norway. We use Alwan and Roberts outlier detection methods to discover any sequence of outlying values in the odds of a live-born twin among male births in exposed birth cohorts.

Results

We find a downward level shift of 27% in the monthly odds of a twin among male births beginning in May and persisting through the remainder of 2020.

Conclusions and implications

Consistent with evolutionary theory and selection in utero, birth cohorts exposed in utero to the onset of the COVID-19 pandemic yielded fewer male twins than expected.

Lay Summary

Our finding of fewer than expected male twin births during the onset of the COVID-19 pandemic provides more evidence that evolution continues to affect the characteristics and health of contemporary populations.

Observable variations in human sex ratio at birth

The human sex ratio at birth (SRB), defined as the ratio between the number of newborn boys to the total number of newborns, is typically slightly greater than 1/2 (more boys than girls) and tends to vary across different geographical regions and time periods. In this large-scale study, we sought to validate previously-reported associations and test new hypotheses using statistical analysis of two very large datasets incorporating electronic medical records (EMRs). One of the datasets represents over half (∼ 150 million) of the US population for over 8 years (IBM Watson Health MarketScan insurance claims) while another covers the entire Swedish population (∼ 9 million) for over 30 years (the Swedish National Patient Register). After testing more than 100 hypotheses, we showed that neither dataset supported models in which the SRB changed seasonally or in response to variations in ambient temperature. However, increased levels of a diverse array of air and water pollutants, were associated with lower SRBs, including increased levels of industrial and agricultural activity, which served as proxies for water pollution. Moreover, some exogenous factors generally considered to be environmental toxins turned out to induce higher SRBs. Finally, we identified new factors with signals for either higher or lower SRBs. In all cases, the effect sizes were modest but highly statistically significant owing to the large sizes of the two datasets. We suggest that while it was unlikely that the associations have arisen from sex-specific selection mechanisms, they are still useful for the purpose of public health surveillance if they can be corroborated by empirical evidences.

The human sex ratio at birth (SRB), usually slightly greater than 1/2, have been reported to vary in response to a wide array of exogenous factors. In the literature, many such factors have been posited to be associated with higher or lower SRBs, but the studies conducted so far have focused on no more than a few factors at a time and used far smaller datasets, thus prone to generating spurious correlations. We performed a series of statistical tests on 2 large, country-wide health datasets representing the United States and Sweden to investigate associations between putative exogenous factors and the SRB, and were able to validate a set of previously-reported associations while also discovering new signals. We propose to interpret these results simply as public health indicators awaiting further empirical confirmation rather than as implicated in (adaptive) sexual selection mechanisms.

The Placenta's Role in Sexually Dimorphic Fetal Growth Strategies

Fetal sex affects the risk of pregnancy complications and the long-term effects of prenatal environment on health. Some have hypothesized that growth strategies differ between the sexes, whereby males prioritize growth whereas females are more responsive to their environment. This review evaluates the role of the placenta in such strategies, focusing on (1) mechanisms underlying sexual dimorphism in gene expression, (2) the nature and extent of sexual dimorphism in placental gene expression, (3) sexually dimorphic responses to nutrient supply, and (4) sexual dimorphism in morphology and histopathology. The sex chromosomes contribute to sex differences in placental gene expression, and fetal hormones may play a role later in development. Sexually dimorphic placental gene expression may contribute to differences in the prevalence of complications such as preeclampsia, although this link is not clear. Placental responses to nutrient supply frequently show sexual dimorphism, but there is no consistent pattern where one sex is more responsive. There are sex differences in the prevalence of placental histopathologies, and placental changes in pregnancy complications, but also many similarities. Overall, no clear patterns support the hypothesis that females are more responsive to the maternal environment, or that males prioritize growth. While male fetuses are at greater risk of a variety of complications, total prenatal mortality is higher in females, such that males exposed to early insults may be more likely to survive and be observed in studies of adverse outcomes. Going forward, robust statistical approaches to test for sex-dependent effects must be more widely adopted to reduce the incidence of spurious results.

Sex-Biased Mortality and Sex Reversal Shape Wild Frog Sex Ratios

Population sex ratio is a key demographic factor that influences population dynamics and persistence. Sex ratios can vary across ontogeny from embryogenesis to death and yet the conditions that shape changes in sex ratio across ontogeny are poorly understood. Here, we address this issue in amphibians, a clade for which sex ratios are generally understudied in wild populations. Ontogenetic sex ratio variation in amphibians is additionally complicated by the ability of individual tadpoles to develop a phenotypic (gonadal) sex opposite their genotypic sex. Because of sex reversal, the genotypic and phenotypic sex ratios of entire cohorts and populations may also contrast. Understanding proximate mechanisms underlying phenotypic sex ratio variation in amphibians is important given the role they play in population biology research and as model species in eco-toxicological research addressing toxicant impacts on sex ratios. While researchers have presumed that departures from a 50:50 sex ratio are due to sex reversal, sex-biased mortality is an alternative explanation that deserves consideration. Here, we use a molecular sexing approach to track genotypic sex ratio changes from egg mass to metamorphosis in two independent green frog (Rana clamitans) populations by assessing the genotypic sex ratios of multiple developmental stages at each breeding pond. Our findings imply that genotypic sex-biased mortality during tadpole development affects phenotypic sex ratio variation at metamorphosis. We also identified sex reversal in metamorphosing cohorts. However, sex reversal plays a relatively minor and inconsistent role in shaping phenotypic sex ratios across the populations we studied. Although we found that sex-biased mortality influences sex ratios within a population, our study cannot say at this time whether sex-biased mortality is responsible for sex ratio variation across populations. Our results illustrate how multiple processes shape sex ratio variation in wild populations and the value of testing assumptions underlying how we understand sex in wild animal populations.

Sexual dimorphism in placental development and its contribution to health and diseases

According to the Developmental Origin of Health and Disease (DOHaD), intrauterine exposure to adverse environments can affect fetus and birth outcomes and lead to long-term disease susceptibility. Evidence has shown that neonatal outcomes and the timing and severity of adult diseases are sexually dimorphic. As the link between mother and fetus, the placenta is an essential regulator of fetal development programming. It is found that the physiological development trajectory of the placenta has sexual dimorphism. Furthermore, under pathological conditions, the placental function undergoes sex-specific adaptation to ensure fetal survival. Therefore, the placenta may be an important mediator of sexual dimorphism in neonatal outcomes and adult disease susceptibility. Few systematic reviews have been conducted on sexual dimorphism in placental development and its underlying mechanisms. In this review, sex chromosomes and sex hormones, as the main reasons for sexual differentiation of the placenta, will be discussed. Besides, in the etiology of fetal-originated adult diseases, overexposure to glucocorticoids is closely related to adverse neonatal outcomes and long-term disease susceptibility. Studies have found that prenatal glucocorticoid overexposure leads to sexually dimorphic expression of placental glucocorticoid receptor isoforms, resulting in different sensitivity of the placenta to glucocorticoids, and may further affect fetal development. The present review examines what is currently known about sex differences in placental development and the underlying regulatory mechanisms of this sex bias. This review highlights the importance of placental contributions to the origins of sexual dimorphism in health and diseases. It may help develop personalized diagnosis and treatment strategies for fetal development in pathological pregnancies.

Projecting sex imbalances at birth at global, regional and national levels from 2021 to 2100: scenario-based Bayesian probabilistic projections of the sex ratio at birth and missing female births based on 3.26 billion birth records

INTRODUCTION

Skewed levels of the sex ratio at birth (SRB) due to sex-selective abortions have been observed in several countries since the 1970s. They will lead to long-term sex imbalances in more than one-third of the world's population with yet unknown social and economic impacts on affected countries. Understanding the potential evolution of sex imbalances at birth is therefore essential for anticipating and planning for changing sex structures across the world.

METHODS

We produced probabilistic SRB projections from 2021 to 2100 based on different scenarios of sex ratio transition and assessed their implications in terms of missing female births at global, regional and national levels. Based on a comprehensive SRB database with 3.26 billion birth records, we project the skewed SRB and missing female births with a Bayesian hierarchical time series mixture model. The SRB projections under reference scenario S1 assumed SRB transitions only for countries with strong statistical evidence of SRB inflation, and the more extreme scenario S2 assumed a sex ratio transition for countries at risk of SRB inflation but with no or limited evidence of ongoing inflation.

RESULTS

Under scenario S1, we projected 5.7 (95% uncertainty interval (1.2; 15.3)) million additional missing female births to occur by 2100. Countries affected will be those already affected in the past by imbalanced SRB, such as China and India. If all countries at risk of SRB inflation experience a sex ratio transition as in scenario S2, the projected missing female births increase to 22.1 (12.2; 39.8) million with a sizeable contribution of sub-Saharan Africa.

CONCLUSION

The scenario-based projections provide important illustrations of the potential burden of future prenatal sex discrimination and the need to monitor SRBs in countries with son preference. Policy planning will be needed in the years to come to minimise future prenatal sex discrimination and its impact on social structures.

Maternal stress and sex ratio at birth in Sweden over two and a half centuries: a retest of the Trivers-Willard hypothesis

STUDY QUESTION

Is there a negative relationship, as predicted in the Trivers–Willard hypothesis (TWH), between the intensity of maternal stress and sex ratio at birth (SRB)?

SUMMARY ANSWER

Using a comprehensive data set with multiple indicators of maternal stress, most measures of stress show no statistically significant association with SRB over a period spanning 243 years, indicating no support for the TWH.

WHAT IS KNOWN ALREADY

Evolutionary biologists have proposed a widely discussed hypothesis that women in poor and stressful conditions during pregnancy are more likely to give birth to girls, and exposure to stressful events may therefore lead to a reduction in sex (male-to-female) ratio at birth. The empirical evidence so far is mixed.

STUDY DESIGN, SIZE, DURATION

Annual time series data, spanning 243 years between 1749 and 1991 for Sweden at the national level, were drawn from multiple sources. The outcome is defined as the percentage of male births relative to all births in Sweden in a given year. The covariates include a set of economic and climatic variables as proxies for maternal stress.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We conduct a series of ARIMA (autoregressive integrated moving average) models to examine the relationship between maternal stress and SRB during three periods: 1749–1991, 1749–1861 and 1862–1991.

MAIN RESULTS AND THE ROLE OF CHANCE

In 1749–1991, economic proxies for maternal stress showed no statistically significant association with SRB. In 1749–1861, two indicators were significantly associated with SRB, but the coefficients were opposite in direction to the TWH. In 1862–1991, five out of six covariates showed no significant association with SRB. An additional analysis found no significant correlation between sex ratio of stillbirths and all covariates in 1862–1991. Our results are incompatible with the TWH and suggest that previous findings in support of the TWH are not robust.

LIMITATIONS, REASONS FOR CAUTION

This study provides population-level evidence that may not necessarily reflect the nature of all individuals due to the ecological fallacy. The time series analysed in this study are annual data, and we cannot examine the potential seasonality due to the lack of disaggregated monthly data. Our findings may not be generalised to the contexts of extreme maternal stress conditions such as famine and war.

WIDER IMPLICATIONS OF THE FINDINGS

The results from existing studies in this topic may be speculative, and additional research with more comprehensive design, data and covariates is needed to reconsider the robustness of previous findings.

STUDY FUNDING/COMPETING INTEREST(S)

The author receives no external funding and has no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Cohort Selection In Utero against Male Twins and Childhood Cancers: A Population-Based Register Study

BACKGROUND

Cancer ranks as the second leading cause of death among children ages 1 to 14 years in the United States. Previous research finds that strong cohort selection in utero against males precedes a reduction in live-born males considered frail. We examine whether such cohort selection in utero may similarly affect the frequency of childhood cancers among male live births.

METHODS

We examined 1,368 childhood cancers among males born in Sweden over 144 months, from January 1990 to December 2001, and followed to age 15 in the Swedish Cancer Registry. We retrieved the count of male twins by birth month from the Swedish Birth Registry. We applied autoregressive, integrated, moving average time-series methods to identify and control for temporal patterns in monthly childhood cancers and to evaluate robustness of results.

RESULTS

Fewer childhood cancers occur among monthly male birth cohorts with elevated selection in utero (i.e., a low count of live-born male twins). This association appears in the concurrent month (coef = 0.04; 95% CI, 0.001-0.079) as well as in the following month in which most births from the twin's conception cohort are "scheduled" to be born (coef = 0.055; 95% CI, 0.017-0.094).

CONCLUSIONS

Elevated cohort selection in utero may reduce the number of frail male gestations that would otherwise have survived to birth and received a cancer diagnosis during childhood.

IMPACT

This novel result warrants further investigation of prenatal exposures, including those at the population level, that may induce cohort selection in utero for some cancer types but not others.

Sex, gender, and retinoblastoma: analysis of 4351 patients from 153 countries

Objective

To investigate in a large global sample of patients with retinoblastoma whether sex predilection exists for this childhood eye cancer.

Methods

A cross-sectional analysis including 4351 treatment-naive retinoblastoma patients from 153 countries who presented to 278 treatment centers across the world in 2017. The sex ratio (male/female) in the sample was compared to the sex ratio at birth by means of a two-sided proportions test at global level, country economic grouping, continent, and for selected countries.

Results

For the entire sample, the mean retinoblastoma sex ratio, 1.20, was higher than the weighted global sex ratio at birth, 1.07 (p < 0.001). Analysis at economic grouping, continent, and country-level demonstrated differences in the sex ratio in the sample compared to the ratio at birth in lower-middle-income countries (n = 1940), 1.23 vs. 1.07 (p = 0.019); Asia (n = 2276), 1.28 vs. 1.06 (p < 0.001); and India (n = 558), 1.52 vs. 1.11 (p = 0.008). Sensitivity analysis, excluding data from India, showed that differences remained significant for the remaining sample (χ² = 6.925, corrected p = 0.025) and for Asia (χ² = 5.084, corrected p = 0.036). Excluding data from Asia, differences for the remaining sample were nonsignificant (χ² = 2.205, p = 0.14).

Conclusions

No proof of sex predilection in retinoblastoma was found in the present study, which is estimated to include over half of new retinoblastoma patients worldwide in 2017. A high male to female ratio in Asian countries, India in specific, which may have had an impact on global-level analysis, is likely due to gender discrimination in access to care in these countries, rather than a biological difference between sexes.

Fisher vs. the Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms that Produce Them

Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two "seminal" contributions of G. A. Parker.