Impact of economic conditions on the secondary sex ratio in a post-communist economy

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.

Association studies between chromosomal regions 1q21.3, 5q21.3, 14q21.2 and 17q21.31 and numbers of children in Poland

Number of children is an important human trait and studies have indicated associations with single-nucleotide polymorphisms (SNPs). Aim: to give further evidence for four associations using a large sample of Polish subjects. Data from the POPULOUS genetic database was provided from anonymous, healthy, unrelated, Polish volunteers of both sexes (N = 5760). SNPs (n = 173) studied: (a) 69 from the chromosome 17 H1/H2 inversion; (b) six from 1q21.3, 5q21.3 and 14q21.2; and (c) 98 random negative controls. Zero-inflated negative-binomial regression (z.i.) was performed (0-3 numbers of children per individual (NCI) set as non-events; adjustors: year of birth, sex). Significance level p = 0.05 with Bonferroni correction. Statistically-significant differences (with data from both sexes combined) were obtained from highly-linked inversion SNPs: representative rs12373123 gave means: homozygotes TT: 2.31 NCI (n = 1418); heterozygotes CT: 2.35 NCI (n = 554); homozygotes CC: 2.44 NCI (n = 43) (genotype p = 0.01; TTvs.CC p = 0.004; CTvs.CC p = 0.009). (Male data alone gave similar results.) Recessive modeling indicated that H2-homozygotes had 0.118 more children than H1-homozygotes + heterozygotes (z.i.-count estimates ± standard errors: CT, - 0.508 ± 0.194; TT, - 0.557 ± 0.191). The non-over-dispersed count model detected no interactions: of importance there was no significant interaction with age. No positive results were obtained from negative-control SNPs or (b). Conclusions: association between the H1/H2 inversion and numbers of children (previously reported in Iceland) has been confirmed, albeit using a different statistical model. One limitation is the small amount of data, despite initially ~ 6000 subjects. Causal studies require further investigation.

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.

Offspring sex ratio: Coital rates and other potential causal mechanisms

In recent years, scientists have begun to pay serious attention to the hypothesis that human parental coital rates around the time of conception causally influences the sexes of subsequent births. In this paper, the grounds of the argument are outlined. The point is important because, if the hypothesis were credible, it can potentially explain one of the best established (and otherwise unexplained) epidemiological features of sex ratio at birth - its rises during and just after World Wars 1 and 2 insofar as increased coital rates increase the ratio. Moreover, the greater the understanding of the variations of sex ratio at birth, the greater will be the understanding of the causes of those selected diseases associated with unusual sex ratios at birth (testicular cancer, hepatitis B, Toxoplasma gondii, and, perhaps, prostatic cancer).

The sex ratio of singleton and twin delivery offspring in assisted reproductive technology in China

In order to evaluate the impact of assisted reproductive technology (ART) procedure and individual factors on the sex ratio of singletons and twins at birth after in vitro fertilization (IVF) and intra-cytoplasmic sperm injection (ICSI) treatment in China. We conducted a retrospective cohort study including patients undergoing their first cycle of IVF or ICSI with autologous oocytes from 2001 to 2015. A total of 7410 babies were born from 5832 women with 7410 live birth. The secondary sex ratio (SSR) in singletons was significantly higher than twins (53.97% vs. 50.89%, P = 0.009). The largest disparity was observed in 'thawed blastocyst embryos ICSI' subgroup that SSR was 59.84% in singletons and 42.45% in twins (P = 0.013). Blastocyst transfer was positively associated with elevated SSR when compared to cleavage stage embryos in singletons (Odds Ratio [OR] = 1.17, P < 0.001). In addition, paternal age was significantly associated with SSR (OR = 0.75, P = 0.014). While the decrease of SSR was significantly associated with ICSI when compared to IVF (OR = 0.61, P = 0.046) in twins. Blastocyst transfer increases SSR in comparing with cleavage stage embryos in singletons, while the use of ICSI reduces SSR in twins. Our findings offered important complement for better understanding the underlying determinant of SSR in ART offspring.

Effect of semen quality on human sex ratio in in vitro fertilization and intracytoplasmic sperm injection: an analysis of 27,158 singleton infants born after fresh single-embryo transfer

OBJECTIVE

To evaluate the effect of semen quality on human sex ratio in in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective cohort study.

SETTING

Not applicable.

PATIENT(S)

A total of 27,158 singleton infants born between 2007 and 2012 after fresh single-embryo transfer.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Proportion of male infants among liveborn infants.

RESULT(S)

There were 14,996 infants born after IVF, 12,164 infants born after ICSI with ejaculated sperm, and 646 infants born after ICSI with nonejaculated sperm. The sex ratio of IVF was 53.1% (95% confidence interval [CI], 52.3-53.9); the sex ratio of ICSI with ejaculated and nonejaculated sperm demonstrated as statistically significant reduction (48.2%; 95% CI, 47.3-49.1 and 47.7%; 95% CI, 43.8-51.6, respectively). In IVF, lower sperm motility, including asthenozoospermia (sperm motility <40%), was associated with a statistically significantly lower sex ratio compared with normal sperm (51.0%; 95% CI, 48.6-53.3 vs. 53.4%; 95% CI, 52.5-54.3). In ICSI with ejaculated sperm, there was no association between sperm motility and sex ratio. Sperm concentration was not associated with sex ratio in both IVF and ICSI.

CONCLUSION(S)

In IVF, lower sperm motility was associated with a statistically significant reduction in sex ratio; ICSI with either ejaculated or nonejaculated sperm was associated with a statistically significant reduction in sex ratio regardless of semen quality.

Live birth sex ratio after in vitro fertilization and embryo transfer in China--an analysis of 121,247 babies from 18 centers

In order to study the impact of procedures of IVF/ICSI technology on sex ratio in China, we conducted this multi-center retrospective study including 121,247 babies born to 93,895 women in China. There were 62,700 male babies and 58,477 female babies, making the sex ratio being 51.8% (Male: Female  = 107∶100). In univariate logistic regression analysis, sex ratio was imbalance toward females of 50.3% when ICSI was preformed compared to 47.7% when IVF was used (P<0.01). The sex ratio in IVF/ICSI babies was significantly higher toward males in transfers of blastocyst (54.9%) and thawed embryo (52.4%) when compared with transfers of cleavage stage embryo (51.4%) and fresh embryo (51.5%), respectively. Multiple delivery was not associated with sex ratio. However, in multivariable logistic regression analysis after controlling for related factors, only ICSI (adjusted OR = 0.90, 95%CI: 0.88–0.93; P<0.01) and blastocyst transfer (adjusted OR = 1.14, 95% CI: 1.09–1.20; P<0.01) were associated with sex ratio in IVF/ICSI babies. In conclusion, the live birth sex ratio in IVF/ICSI babies was influenced by the use of ICSI, which may decrease the percentage of male offspring, or the use of blastocyst transfer, which may increase the percentage of male offspring.

The effect of the season of birth and of selected maternal factors on linear enamel thickness in modern human deciduous incisors

OBJECTIVE

Development of human tooth enamel is a part of a foetus's development; its correctness is the outcome of genetic and maternal factors shaping its prenatal environment. Many authors reported that individuals born in different seasons experience different early developmental conditions during pregnancy. In this study, we investigated the effects of season of birth and selected maternal factors on enamel thickness of deciduous incisors.

DESIGN

Dental sample comprises 60 deciduous incisors. The parents who handed over their children's teeth for research fill in questionnaires containing questions about the course of pregnancy. All teeth were sectioned in the labio-linqual plane using diamond blade (Buechler IsoMet 1000). The final specimens were observed by way of scanning electron microscopy at magnifications 80× and 320×. The thickness of total enamel (TE), prenatally (PE) and postnatally (PSE) formed enamel was measured.

RESULTS

Children born in summer and in spring (whose first and second foetal life fall on autumn and winter) have the thinnest enamel. Season of birth, number of children in family, diseases and spasmolytic medicines using by mother during pregnancy explained almost 13% of the variability of TE. Regression analysis proved a significant influence of the season of birth and selected maternal factors on the PE thickness - these factors explained over 17% of its variability. Neither of analysed variables had influenced PSE.

CONCLUSIONS

Our findings suggests that the thickness of enamel of deciduous incisors depends on the season of birth and some maternal factors. The differences were observed only in the prenatally formed enamel.

Frequency of under- and overweight among children and adolescents during the economic transition in Poland

The aim of this study is to examine the prevalence of underweight, overweight and obesity, using International Obesity Task Force (IOTF) criteria, in four cohorts of children and adolescents living in Poland in different economic eras: communist economy (1977/1978), crisis of the 1980s (1987/1988), political and economic transformation (1992/1994) and the free market economy (2002/2004). Analysis was conducted on a database including 10,934 records for children of the age 7-18 years. In Poland, in the last 26 years of economic and political transformations, the epidemic of obesity was not noticed but the growing incidence of children and adolescents with body mass deficit was observed (p<0.0001) (20.2% of girls in 2002/2004 vs. 11.0% in 1977/1978 and 12.1% of boys in 2002/2004 vs. 7.2% in 1977/1978). Lower parental education and a higher number of children in a family resulted in a higher prevalence of underweight (odds ratio [OR] fluctuated from 1.26 to 1.63). The social effects of the political transformation in Poland significantly affected families with low socio-economic status (SES), and especially more eco-sensitive boys. This result is opposite to the trends observed in Western countries and makes an important contribution to the current knowledge of the course of further changes in weight-to-height ratio at a global scale.