Sex ratio at birth following prenatal maternal exposure to severe life events: a population-based cohort study

Maternal Risk Factors Associated with Preterm Births among Pregnant Women in Mogadishu, Somalia

Background: Premature birth impacts millions of newborns annually. Sixty percent of the world’s preterm births occur in Sub-Saharan Africa and South Asia. Somalia’s premature birth rates and maternal risk factors are poorly studied; hence, this study aims to identify maternal risk factors related to premature births in Mogadishu, Somalia. Methods: This unmatched case-control study was conducted at four maternity hospitals in Mogadishu, Somalia. The cases were newborns with gestational ages of less than 37 weeks; controls were newborns with gestational ages of 37 to 42 weeks. All were live singletons. Cross-tabulation and binary logistic regression were used to analyze the data; a p-value of 0.05 was deemed statistically significant. Result: Of the total of 499 newborns, 70 were cases, and 429 were controls. Adequate prenatal care, maternal urine analysis, tetanus toxoid (TT) vaccination, hemoglobin (Hb) measurement, ultrasound monitoring, intake of iron + folic acid (IFA) supplement, blood pressure (BP) measurement during the current pregnancy, as well as partograph usage during labor all significantly decreased risk of having premature births. A prior history of preterm delivery and preeclampsia, obstetric complications, and female genital mutilation (FGM) significantly increased the risk of preterm births. Conclusion: The utilization of antenatal care services, use of a partograph, obstetric complications, and prior history of premature birth and preeclampsia had a substantial effect on preterm birth rates. This study identifies female genital mutilation (FGM) as a previously unidentified risk factor for preterm birth that needs additional investigation.

A preliminary analysis of the secondary sex ratio decline after the COVID-19 pandemic in Japan

Objectives

The secondary sex ratio (SSR, i.e., the number of male births per 100 female births) has long been proposed as a sentinel health indicator. Studies have suggested that exogenous environmental stressors reduce SSR after 3 to 6 months (via disproportionate male fetus deaths) and after 9 months (via reduced male conception). We aimed to examine whether SSR declined after the coronavirus disease 2019 (COVID‐19) pandemic in Japan.

Methods

We used monthly vital statistics records collected between January 2013 and April 2021 (the ‐number of male and female live births, in particular). Using information reported before the pandemic struck Japan (i.e., January 2013 to January 2020), we predicted SSRs for the months after the pandemic (i.e., February 2020 to April 2021) and compared reported and predicted SSRs. We also stratified the analysis by including two groups of prefectures with different degrees of possible influence from the pandemic.

Results

We observed a significant reduction in SSR during December 2020 of 102.81 (i.e., 9–10 months after the pandemic affected the country), which was below the lower bound of the 95% prediction intervals (103.12–106.33). This was the lowest SSR observed during the 100‐month study period. In addition, the reduction in SSR during December 2020 was more pronounced in the more seriously affected prefectures.

Conclusion

In Japan, we found a significant reduction in SSR (i.e., fewer male live births) 9–10 months after COVID‐19 was declared a pandemic. This suggests the onset of the COVID‐19 pandemic was a significant population‐level stressor.

The sex ratio at birth in France was unchanged 9months after the 1998 FIFA World Cup

INTRODUCTION

Positive psychological phenomena such as increased feelings of belonging linked to hosting the FIFA World Cup were observed in France 1998 and South Africa 2010. Approximately nine months after South Africa hosted the 2010 World Cup the sex ratio at birth increased significantly. Given the similarity of positive psychological phenomena between the two countries, this study sought to determine if the sex ratio at birth increased in France circa nine months after the 1998 World Cup.

METHODS

Anonymized publicly available live birth data from 1994 to 2004 inclusive was obtained from the Insee (Institut National de la Statistique et des Etudes/Économiques - National Institute of Statistics and Economic Studies). For statistical analysis, chi-squared tests were used.

RESULTS

The sex ratio at birth for March and April 1999 did not differ significantly from that of the rest of same period from 1996 to 2000 (p=0.558), there was also no significant difference for February and March 1999.

CONCLUSION

The sex ratio at birth did not increase in France after it hosted the 1998 World Cup. Possible reasons why the sex ratio at birth did not increase as it did in South Africa include a higher French prevalence of modern contraceptive use and a different kind/level of excitement for the World Cup in France since it has previously hosted large international sports tournaments. The influence of the World Cup on the sex ratio at birth depends on the context of a specific country.

Changes in Income at Macro Level Predict Sex Ratio at Birth in OECD Countries

The human sex ratio at birth (SRB) is approximately 107 boys for every 100 girls. SRB was rising until the World War II and has been declining slightly after the 1950s in several industrial countries. Recent studies have shown that SRB varies according to exposure to disasters and socioeconomic conditions. However, it remains unknown whether changes in SRB can be explained by observable macro-level socioeconomic variables across multiple years and countries. Here we show that changes in disposable income at the macro level positively predict SRB in OECD countries. A one standard deviation increase in the change of disposable income is associated with an increase of 1.03 male births per 1000 female births. The relationship is possibly nonlinear and driven by extreme changes. The association varies from country to country being particular strong in Estonia. This is the first evidence to show that economic and social conditions are connected to SRB across countries at the macro level. This calls for further research on the effects of societal conditions on general characteristics at birth.

Periconceptional Multivitamin Supplementation Containing Folic Acid and Sex Ratio at Birth in a Chinese Population: a Prospective Cohort Study

BACKGROUND

To determine whether periconceptional use of multivitamin supplements containing folic acid increases the occurrence of male births in a Chinese population.

METHODS

A prospective cohort study was carried out in 18 counties in four provinces of China. Participants were naturally and voluntarily divided into an intervention group (who took a multivitamin pill containing folic acid, n = 25,418) and a control group (who did not take any multivitamin, n = 26,580). Multivitamin supplements containing folic acid was ascertained before pregnancy. Pregnant women were followed through the first trimester of pregnancy and the outcome of pregnancy (i.e. livebirth, stillbirth, or fetal death; sex at birth) was recorded.

RESULTS

A total of 52,043 pregnancies and 51,998 births were recorded between September 2000 and August 2002. The proportion of males born to women who did and did not take the multivitamin were 54.8% (n = 13,935) and 54.0% (n = 11,483), respectively. The male to female sex ratios at birth among women who did and did not take the multivitamin were 117:100 and 121:100, respectively. The risk ratio was 1.03 [95% confidence interval 0.99, 1.06] after adjusting for confounding factors.

CONCLUSIONS

These findings suggest that periconceptional multivitamin supplementation containing folic acid is not associated with an increased likelihood of male births in a Chinese population. However, these results may have been affected by induced abortion or selective termination of pregnancy, and the findings must therefore be cautiously interpreted.

The Great Recession of 2007 in the United States and the male: female ratio at birth

OBJECTIVE

Male live births slightly exceed female live births by approximately 3%. The ratio of male to total live births is conventionally represented as M/F. Many factors have been shown to affect M/F, mainly privation, toxins, and stress, all of which reduce M/F. Population stress may be engendered by natural phenomena such as earthquakes and man-made events such as short wars, terrorist attacks, and contracting economies. This study was conducted to ascertain whether the onset of the "Great Recession" (2007) was associated with changes in M/F in the United States (US).

MATERIAL AND METHODS

Annual monthly live births by gender for January 2006 to December 2008 were obtained from United States Centres for Disease Control and Prevention.

RESULTS

In 2007, there were 4316233 live births [M/F: 0.51157; 95% confidence intervals: 0.51110-0.51205). M/F rose between January and June, and then fell sharply between August and December. M/F was statistically significantly lower in the second half of 2007 (p=0.007). The dip in M/F from June to July was also significant (p=0.02). These findings were not replicated in the amalgamated data for 2006 and 2008.

CONCLUSION

The United States housing boom of the mid-2000s was fueled by rising house prices and cheap mortgages given to credit-poor buyers. A halt in rising house prices resulted in defaults and foreclosures, triggering the worst financial crisis since the Great Depression. The associated stress appears to have decreased M/F in the US.

Multi-factorial influences on sex ratio: a spatio-temporal investigation of endocrine disruptor pollution and neighborhood stress

Background:

It is suggested the declining male birth proportion in some industrialized countries is linked to ubiquitous endocrine disruptor exposure. Stress and advanced parental age are determinants which frequently present positive findings. Multi-factorial influences on population sex ratio are rarely explored or tested in research.

Objectives:

To test the hypothesis that dual factors of pollution and population stress affects sex proportion at birth through geographical analysis of Central Scotland.

Methods:

The study incorporates the use of Geographical Information Systems (GIS) tools to overlay modeled point source endocrine disruptor air emissions with “small-area” data on multiple deprivation (a proxy measurement of stress) and birth sex. Historical review of regional sex ratio trends presents additional data on sex ratio in Scotland to consider.

Results:

There was no overall concentration in Central Scotland of low sex ratio neighborhoods with areas where endocrine disruptor air pollution and deprivation or economic stress were high. Historical regional trends in Scotland (from 1973), however, do show significantly lower sex ratio values for populations where industrial air pollution is highest (i.e. Eastern Central Scotland).

Conclusions:

Use of small area data sets and pollution inventories is a potential new method of inquiry for reproductive environmental and health protection monitoring and has produced interesting findings.

The primary parental investment in children in the contemporary USA is education : Testing the Trivers-Willard hypothesis of parental investment

This paper tests the Trivers-Willard hypothesis that high-status individuals will invest more in sons and low-status individuals will invest more in daughters using data from the 2000 to 2010 General Social Survey and the 1979 National Longitudinal Survey of Youth. We argue that the primary investment U.S. parents make in their children is in their children's education, and this investment is facilitated by a diverse market of educational choices at every educational level. We examine two measures of this investment: children's years of education and the highest degree attained. Results show that sons of high-status fathers receive more years of education and higher degrees than daughters, whereas daughters of low-status fathers receive more years of education and higher degrees than sons. Further analyses of possible mechanisms for these findings yield null results. We also find that males are more likely to have high-status fathers than females.

Impact of earthquakes on sex ratio at birth: Eastern Marmara earthquakes

OBJECTIVE

Previous reports suggest that maternal exposure to acute stress related to earthquakes affects the sex ratio at birth. Our aim was to examine the change in sex ratio at birth after Eastern Marmara earthquake disasters.

MATERIAL AND METHODS

This study was performed using the official birth statistics from January 1997 to December 2002 - before and after 17 August 1999, the date of the Golcuk Earthquake - supplied from the Turkey Statistics Institute. The secondary sex ratio was expressed as the male proportion at birth, and the ratio of both affected and unaffected areas were calculated and compared on a monthly basis using data from gender with using the Chi-square test.

RESULTS

We observed significant decreases in the secondary sex ratio in the 4th and 8th months following an earthquake in the affected region compared to the unaffected region (p= 0.001 and p= 0.024). In the earthquake region, the decrease observed in the secondary sex ratio during the 8th month after an earthquake was specific to the period after the earthquake.

CONCLUSION

Our study indicated a significant reduction in the secondary sex ratio after an earthquake. With these findings, events that cause sudden intense stress such as earthquakes can have an effect on the sex ratio at birth.

O sexo masculino vulnerável: razão de masculinidade entre os óbitos fetais brasileiros

Alguns estudos apontam para a existência de vulnerabilidades biológicas inatas masculinas, especialmente no período perinatal. Foi realizada uma análise transversal da mortalidade fetal brasileira segundo sexo, entre 2000 e 2009 (inclusive), conforme características maternas (idade, escolaridade e duração da gestação), utilizando-se dados disponibilizados pelos sistema DATASUS do Ministério da Saúde. Todos os óbitos fetais do período foram incluídos na análise, excetuando-se os casos em que o sexo do feto não foi declarado. A razão de masculinidade (RM) encontrada para os óbitos fetais foi de 1,188. As categorias mais relacionadas com maior risco (idade entre 10 e 14 anos, nenhuma escolaridade e gestação com menos de 22 semanas) apresentaram maior RM, sendo esses valores, em todos os casos, estatisticamente maiores do que os observados nas outras categorias analisadas (p < 0,05). Verificou-se RM estatisticamente maior (p < 0,05) ao esperado para 13 causas básicas de óbito e menor para duas. Os resultados encontrados pelo estudo apontam para uma possível vulnerabilidade biológica inata masculina.

[Age-, period-, and birth-cohort-specific effects on the male proportion in Japanese newborns and projections for male proportion for 20 periods (2008-2027)]

OBJECTIVES

To determine the age-, period-, and cohort-specific effects on the male proportion in Japanese newborns, we performed an age-period-cohort (APC) analysis in this study. In addition, projections for the male proportion were analyzed.

METHODS

We obtained data on live births of newborns for Japanese women in 1947-2007 from the National Vital Statistics. Cohort tables containing data on the male proportion were analyzed using a Bayesian APC model. Projections of the male proportion (2008-2027) were calculated.

RESULTS

The age effect decreased when the mothers were 40-44 years old; however, the effect was relatively limited as compared with the period and cohort effects. The period effect increased from 1947 to 1969 and decreased thereafter. Analysis of the cohort effect on male proportion trends revealed a decreasing slope for birth cohorts born between 1905 and 1945 and a subsequent increase after 1958. The projections for male proportion indicated that the male proportion in 2027 would be similar to that in the 1970s.

CONCLUSIONS

The age of the mother hardly affected the male proportion. The period effect started decreasing from the latter half of the 1960s. This may be attributable to the high economic growth since 1965 that promoted industrial development that led to environmental pollution, which in turn may have lead to the deterioration of the intrauterine environment. Cohort effects changed from 1958 and exhibited trends toward increase in male proportion; this may be due to improvements in obstetric care. Our results suggest that the male proportion in Japanese newborns will increase in the future.

H-Y antibody titers are increased in unexplained secondary recurrent miscarriage patients and associated with low male : female ratio in subsequent live births

BACKGROUND

The birth of a boy is significantly more common than a girl prior to secondary recurrent miscarriage (SRM) and is associated with a poorer chance of a subsequent live birth. Children born after SRM are more likely to be girls. High-titer antisera specific for male antigens (H-Y) have been shown to arrest development of male bovine embryos efficiently. We consequently questioned the role of H-Y antibodies in women with SRM.

METHODS

Serum samples from patients with unexplained SRM (n = 84), unexplained primary recurrent miscarriage (PRM) (n = 12) and healthy women (n = 37) were obtained. The samples were taken during pregnancy (gestational weeks 4-5) for 77 (80%) of the patients. Enzyme-linked immunosorbent assay was used to detect immunoglobulin G antibodies that specifically recognized any of the five recombinant H-Y proteins (EIF1AY, RPS4Y1, ZFY, DDX3Y and UTY) and their H-X homologs.

RESULTS

H-Y-specific antibodies were more frequent in SRM patients (46%) compared with female controls (19%, P = 0.004) and PRM patients (8%, P = 0.01). The presence of H-Y antibodies in early pregnancy was associated with a low male: female birth ratio among the subsequent live births, as only 12% of children born to H-Y antibody-positive patients were boys compared with 44% boys born to H-Y antibody negative patients (P = 0.03).

CONCLUSIONS

The high frequency of H-Y antibody-positive SRM patients and the association between the presence of these antibodies in early pregnancy and the low number of male offspring, suggest that maternal immune responses against H-Y antigens can cause pregnancy losses. Further exploring these mechanisms may increase our understanding of unexplained SRM.

Mother's occupation and sex ratio at birth

Background

Many women are working outside of the home, occupying a multitude of jobs with varying degrees of responsibilities and levels of psychological stress. We investigated whether different job types in women are associated with child sex at birth, with the hypothesis that women in job types, which are categorized as "high psychological stress" jobs, would be more likely to give birth to a daughter than a son, as females are less vulnerable to unfavourable conditions during conception, pregnancy and after parturition, and are less costly to carry to term.

Methods

We investigated the effects of mother's age, maternal and paternal job type (and associated psychological stress levels) and paternal income on sex ratio at birth. Our analyses were based on 16,384 incidences of birth from a six-year (2000 to 2005 inclusive) childbirth dataset from Addenbrooke's Hospital in Cambridge, UK. We obtained a restricted data set from Addenbrooke's hospital with: maternal age, maternal and paternal occupations, and whether or not the child was first-born.

Results

Women in job types that were categorized as "high stress" were more likely to give birth to daughters, whereas women in job types that were categorized as "low stress" had equal sex ratios or a slight male bias in offspring. We also investigated whether maternal age, and her partner's income could be associated with reversed offspring sex ratio. We found no association between mother's age, her partner's job stress category or partner income on child sex. However, there was an important interaction between job stress category and partner income in some of the analyses. Partner income appears to attenuate the association between maternal job stress and sex ratios at moderate-income levels, and reverse it at high-income levels.

Conclusions

To our knowledge this is the first report on the association between women's job type stress categories and offspring sex ratio in humans, and the potential mitigating effect of their partners' income.