Smoking habits of parents and male: female ratio in spermatozoa and preimplantation embryos

Effects of earthquakes and other natural catastrophic events on the sex ratio of newborn infants

Stress due to earthquakes and other natural catastrophic events may result in a decline in the male to female ratio of newborn infants. One reason may be an increased death of male fetuses 3-5 months earlier. Another reason may relate to reduced conception of males and/or early male embryo demise 8-10 months earlier. Almost all of the earthquakes and natural catastrophic events have caused declines in sex ratios at birth except the Hurricane Katrina which showed a rise in the birth sex ratio. We describe hypothetical immunological cause for the decline in the sex ratio at birth following periods of augmented stress levels.

Secondary sex ratio in assisted reproduction: an analysis of 1 376 454 treatment cycles performed in the UK

STUDY QUESTION

Does ART impact the secondary sex ratio (SSR) when compared to natural conception?

SUMMARY ANSWER

IVF and ICSI as well as the stage of embryo transfer does impact the overall SSR.

WHAT IS KNOWN ALREADY

The World Health Organization quotes SSR for natural conception to range between 103 and 110 males per 100 female births.

STUDY DESIGN SIZE DURATION

A total of 1 376 454 ART cycles were identified, of which 1 002 698 (72.8%) cycles involved IVF or ICSI. Of these, 863 859 (85.2%) were fresh cycles and 124 654 (12.4%) were frozen cycles. Missing data were identified in 14 185 (1.4%) cycles.

PARTICIPANTS/MATERIALS SETTING METHODS

All cycles recorded in the anonymized UK Human Fertilisation and Embryology Authority (HFEA) registry database between 1991 and 2016 were analysed. All singleton live births were included, and multiple births were excluded to avoid duplication.

MAIN RESULTS AND THE ROLE OF CHANCE

The overall live birth rate per cycle for all IVF and ICSI treatments was 26.2% (n = 262 961), and the singleton live birth rate per cycle was 17.1% (n = 171 399). The overall SSR for this study was 104.0 males per 100 female births (binomial exact 95% CI: 103.1-105.0) for all IVF and ICSI cycles performed in the UK recorded through the HFEA. This was comparable to the overall SSR for England and Wales at 105.3 males per 100 female births (95% CI: 105.2-105.4) from 1991 to 2016 obtained from the Office of National Statistics database. Male predominance was seen with conventional insemination in fresh IVF treatment cycles (SSR 110.0 males per 100 female births; 95% CI: 108.6-111.5) when compared to micro-injection in fresh ICSI treatment cycles (SSR 97.8 males per 100 female births; 95% CI: 96.5-99.2; odds ratio (OR) 1.16, 95% CI 1.12-1.19, P < 0.0001), as well as with blastocyst stage embryo transfers (SSR 104.8 males per 100 female births; 95% CI: 103.5-106.2) when compared to a cleavage stage embryo transfer (SSR 101.2 males per 100 female births; 95% CI: 99.3-103.1; OR 1.03, 95% CI 1.01-1.06, P = 0.011) for all fertilization methods.

LIMITATIONS REASONS FOR CAUTION

The quality of the data relies on the reporting system. Furthermore, success rates through ART have improved since 1991, with an increased number of blastocyst stage embryo transfers.

WIDER IMPLICATIONS OF THE FINDINGS

This is the largest study to date evaluating the impact of ART on SSR. The results demonstrate that, overall, ART does have an impact on the SSR when assessed according to the method of fertilization (ICSI increased female births while IVF increased males). However, given the ratio of IVF to ICSI cycles at present with 60% of cycles from IVF and 40% from ICSI, the overall SSR for ART closely reflects the population SSR for, largely, natural conceptions in England and Wales.

STUDY FUNDING/COMPETING INTERESTS

The study received no funding. C.M.B. is a member of the independent data monitoring group for a clinical endometriosis trial by ObsEva. He is on the scientific advisory board for Myovant and medical advisory board for Flo Health. He has received research grants from Bayer AG, MDNA Life Sciences, Volition Rx and Roche Diagnostics as well as from Wellbeing of Women, Medical Research Council UK, the NIH, the UK National Institute for Health Research and the European Union. He is the current Chair of the Endometriosis Guideline Development Group for ESHRE and was a co-opted member of the Endometriosis Guideline Group by the UK National Institute for Health and Care Excellence (NICE). I.G. has received research grants from Wellbeing of Women, the European Union and Finox.

TRIAL REGISTRATION NUMBER

Not applicable.

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.

From sperm to offspring: Assessing the heritable genetic consequences of paternal smoking and potential public health impacts

Individuals who smoke generally do so with the knowledge of potential consequences to their own health. What is rarely considered are the effects of smoking on their future children. The objective of this work was to review the scientific literature on the effects of paternal smoking on sperm and assess the consequences to offspring. A literature search identified over 200 studies with relevant data in humans and animal models. The available data were reviewed to assess the weight of evidence that tobacco smoke is a human germ cell mutagen and estimate effect sizes. These results were used to model the potential increase in genetic disease burden in offspring caused by paternal smoking, with specific focus on aneuploid syndromes and intellectual disability, and the socioeconomic impacts of such an effect. The review revealed strong evidence that tobacco smoking is associated with impaired male fertility, and increases in DNA damage, aneuploidies, and mutations in sperm. Studies support that these effects are heritable and adversely impact the offspring. Our model estimates that, with even a modest 25% increase in sperm mutation frequency caused by smoke-exposure, for each generation across the global population there will be millions of smoking-induced de novo mutations transmitted from fathers to offspring. Furthermore, paternal smoking is estimated to contribute to 1.3 million extra cases of aneuploid pregnancies per generation. Thus, the available evidence makes a compelling case that tobacco smoke is a human germ cell mutagen with serious public health and socio-economic implications. Increased public education should be encouraged to promote abstinence from smoking, well in advance of reproduction, to minimize the transmission of harmful mutations to the next-generation.

Environmental PAH exposure and male idiopathic infertility: a review on early life exposures and adult diagnosis

The male reproductive system is acutely and uniquely sensitive to a variety of toxicities, including those induced by environmental pollutants throughout the lifespan. Early life hormonal and morphological development results in several especially sensitive critical windows of toxicity risk associated with lifelong decreased reproductive health and fitness. Male factor infertility can account for over 40% of infertility in couples seeking treatment, and 44% of infertile men are diagnosed with idiopathic male infertility. Human environmental exposures are poorly understood due to limited available data. The latency between maternal and in utero exposure and a diagnosis in adulthood complicates the correlation between environmental exposures and infertility. The results from this review include recommendations for more and region specific monitoring of polycyclic aromatic hydrocarbon (PAH) exposure, longitudinal and clinical cohort considerations of exposure normalization, gene-environment interactions, in utero exposure studies, and controlled mechanistic animal experiments. Additionally, it is recommended that detailed semen analysis and male fertility data be included as endpoints in environmental exposure cohort studies due to the sensitivity of the male reproductive system to environmental pollutants, including PAHs.

Changes in sex ratio from fertilization to birth in assisted-reproductive-treatment cycles

BACKGROUND

In Western gender-neutral countries, the sex ratio at birth is estimated to be approximately 1.06. This ratio is lower than the estimated sex ratio at fertilization which ranges from 1.07 to 1.70 depending on the figures of sex ratio at birth and differential embryo/fetal mortality rates taken into account to perform these estimations. Likewise, little is known about the sex ratio at implantation in natural and assisted-reproduction-treatment (ART) cycles. In this bioessay, we aim to estimate the sex ratio at fertilization and implantation using data from embryos generated by standard in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) in preimplantation genetic diagnosis cycles. Thereafter, we compare sex ratios at implantation and birth in cleavage- and blastocyst-stage-transfer cycles to propose molecular mechanisms accounting for differences in post-implantation male and female mortality and thereby variations in sex ratios at birth in ART cycles.

METHODS

A literature review based on publications up to December 2013 identified by PubMed database searches.

RESULTS

Sex ratio at both fertilization and implantation is estimated to be between 1.29 and 1.50 in IVF cycles and 1.07 in ICSI cycles. Compared with the estimated sex ratio at implantation, sex ratio at birth is lower in IVF cycles (1.03 after cleavage-stage transfer and 1.25 after blastocyst-stage transfer) but similar and close to unity in ICSI cycles (0.95 after cleavage-stage transfer and 1.04 after blastocyst-stage transfer).

CONCLUSIONS

In-vitro-culture-induced precocious X-chromosome inactivation together with ICSI-induced decrease in number of trophectoderm cells in female blastocysts may account for preferential female mortality at early post-implantation stages and thereby variations in sex ratios at birth in ART cycles.

Paternal smoking habits affect the reproductive life span of daughters

The present study assessed whether the smoking habits of fathers around the time of conception affected the period in which daughters experienced menstrual cycles (i.e., the reproductive life span). The study revealed that the smoking habits of the farther shortened the daughters' reproductive life span compared with daughters whose fathers did not smoke.

Maternal socioeconomic and demographic factors associated with the sex ratio at birth in Vietnam

In recent years Vietnam has experienced a high sex ratio at birth (SRB) amidst rapid socioeconomic and demographic changes. However, little is known about the differentials in SRB between maternal socioeconomic and demographic groups. The paper uses data from the annual Population Change Survey (PCS) in 2006 to examine the relationship of the sex ratio of the most recent birth with maternal socioeconomic and demographic characteristics and the number of previous female births. The SRB of Vietnam was significantly high at 111.4 (95% CI 109.7-113.1) for the period 1st April 2000 to 31st March 2006. Multivariate analysis reveals that sex of the most recent birth is strongly related with the number of previous female births. This association is consistent across different socioeconomic and demographic groups of women. Given the high SRB in Vietnam, further research into the reasons for high SRB in these groups is required, as are intervention programmes such as those raising the public awareness of its negative consequences.

Association between socio-psycho-behavioral factors and male semen quality: systematic review and meta-analyses

OBJECTIVE

To identify the factors associated with male semen quality from many socio-psycho-behavioral factors.

DESIGN

Medline/PubMed, EMBASE, and CNKI were searched to identify relevant publications for systematic review and meta-analysis.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Thirteen socio-psycho-behavioral factors in 57 cross-sectional studies with 29,914 participants from 26 countries/regions were involved in this review. Six factors (age, body mass index [BMI], psychological stress, smoking, alcohol, and coffee consumption) were included in meta-analyses.

RESULT(S)

Smoking can deteriorate all of the sperm parameters of both fertile and infertile men, but it is not risk factor for semen volume in Switzerland and Iran and for sperm density in the United States, Denmark, and Brazil; higher age and alcohol consumption are risk factors for lower semen volume; and psychological stress can lower sperm density and sperm progressive motility and increase abnormal sperm.

CONCLUSION(S)

This review further suggested that higher age, smoking, alcohol consumption, and psychological stress were risk factors for semen quality. These results indicated that health programs focusing on lifestyle and psychological health would be helpful for male reproductive health. Well-designed studies are needed to further identify the role of more socio-psycho-behavioral factors in male semen quality.

Effect of sperm DNA fragmentation on pregnancy outcome depends on oocyte quality

OBJECTIVE

To quantify the effect of sperm DNA fragmentation (SDF) on reproductive outcome by evaluating the most statistically significant bias factors using logistic regression.

DESIGN

Prospective blind observational cohort study.

SETTING

University affiliated private IVF unit.

PATIENT(S)

Two hundred ten male partners of couples undergoing in vitro fertilization (IVF) or first intracytoplasmic sperm injection (ICSI) cycles with fresh or thawed sperm with the women's own or donated oocytes.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

SDF determined before and after swim-up (n=420), odds ratio calculated of the effect of an increase of one unit of SDF on pregnancy, and stratified regression analysis performed to evaluate the confusion effect of oocyte quality, sperm origin, and the fertilization procedure.

RESULT(S)

The effect of SDF on pregnancy was not affected by sperm origin (fresh or thawed) or fertilization procedure when measured both before and after swim-up. When oocytes from infertile patients were employed, SDF had a statistically significant negative impact on chance of pregnancy. For every 10% increase in SDF, the probability of not achieving pregnancy increased by 1.31. When donated oocytes were employed, SDF did not have a statistically significant effect.

CONCLUSION(S)

The effect of SDF on the probability of pregnancy can be calculated independent of the fertilization procedure or sperm origin. Oocyte quality conditions the extent of the negative impact of SDF on pregnancy; this can be overcome when good quality oocytes are employed.

Parental smoking and increased likelihood of female births

BACKGROUND

A recent decline in the male:female (M:F) sex ratio may relate to pregnancy cigarette smoke exposure.

AIM

To assess trends and cigarette exposure dose-response effects on the sex ratio.

SUBJECTS AND METHODS

A retrospective analysis was carried out of deliveries at the Liverpool Women's Hospital between 1998 and 2003, and of deliveries reported in community surveys from the same area in 1998 and 2006.

RESULTS

For the hospital sample, the M:F sex ratio was 1.14 if no parent smoked, and 0.77 when both parents smoked during the mother's pregnancy (p < 0.001). Heavy maternal smokers (>10 cigarettes per day) were more likely to deliver a female baby than light smokers (p < 0.001). Smoking was associated with increased likelihood of female birth controlling for birth year, socio-economic status, alcohol exposure, maternal haemoglobin and body mass index (adjusted OR: 1.41, 95% CI 1.12-1.92, p < 0.001). In the community sample controlling for socio-economic status the ratios were 1.13 (95% CI 1.03-1.24, p = 0.015) in 1998 and 1.31 (95% CI 1.16-1.48, p < 0.001) in 2006. Secular trends showed decreasing ratios in hospital and community samples for both smokers and non-smokers.

CONCLUSION

Pregnancy cigarette smoking increased the proportion of female births with evidence for a dose-response association.

Female genital cutting and mother's age at birth are associated with the sex of offspring in Africa

Female genital cutting (FGC) is widespread in Africa. Its short and long term medical consequences are widely reported. Here we report that FGC is associated with and may contribute to increases in the sex ratio at birth (Odds Ratio = 1.019; 95% C.I. = 1.007, 1.032) while mother's age at birth is inversely associated with probability of male birth (Odds Ratio = 0.998; 95% C.I. = 0.997, 0.999) in a generalized linear, logistic model with the probability of a male birth the dependent variable and eight potential explanatory variables applied to 413,384 births in 22 African countries. While these two associations are statistically significant, their odds ratios are close to 1.0 and they only slightly decrease the null deviance of the model. Therefore sex determination in these data is still a mostly stochastic process determined by the random variation in X or Y sperm production, transport, and conception.

Sperm selection by swim-up in terms of deoxyribonucleic acid fragmentation as measured by the sperm chromatin dispersion test is altered in heavy smokers

Toxic habits and their relationship with male factor infertility have been a matter of investigation in recent years, and smoking is one of the most common lifestyle toxic exposures to harmful substances. The analysis of sperm deoxyribonucleic acid fragmentation after capacitation detected a detrimental effect produced by tobacco, and this deleterious effect alters the sperm swim-up selection process in smokers, although the molecular and cellular basis of this phenomenon remain to be elucidated.

Preconception maternal polychlorinated biphenyl concentrations and the secondary sex ratio

The secondary sex ratio is the ratio of male to female live births and historically has ranged from 102 to 106 males to 100 females. Temporal declines have been reported in many countries prompting authors to hypothesize an environmental etiology. Blood specimens were obtained from 99 women aged 24-34 prior to attempting pregnancy and quantified for 76 polychlorinated biphenyl (PCB) congeners using dual column gas chromatography with electron capture detection. Women were prospectively followed until pregnancy or 12 cycles of trying. The odds of a male birth for three PCB groupings (total, estrogenic, anti-estrogenic) controlling for maternal characteristics were estimated using logistic regression. Among the 50 women with live births and PCB data, 26 female and 24 male infants were born (ratio 0.92). After adjusting for age and body mass index, odds of a male birth were elevated among women in the second (OR=1.29) and third (OR=1.48) tertiles of estrogenic PCBs; odds (OR=0.70) were reduced among women in the highest tertile of anti-estrogenic PCBs. All confidence intervals included one. The direction of the odds ratios in this preliminary study varied by PCB groupings, supporting the need to study specific PCB patterns when assessing environmental influences on the secondary sex ratio.

Embryonic loss due to exposure to polycyclic aromatic hydrocarbons is mediated by Bax

The high miscarriage rates observed in women smokers raises the possibility that chemicals in cigarette smoke could be detrimental to embryo development. Previous studies have established that polycyclic aromatic hydrocarbons (PAHs), transactivate the arylhydrocarbon receptor (AhR), leading to cell death. Herein we show that PAH exposure results in murine embryo cell death, acting as a potential mechanism underlying cigarette-smoking-induced pregnancy loss. Cell death was preceded by increases in Bax levels, activation of caspase-3 and decreased litter size. Chronic exposure of females to PAHs prior to conception impaired development, resulting in a higher number of resorptions. This embryonic loss could not be prevented by the disruption of Hrk, but was diminished in embryos lacking Bax. We conclude that exposure of early embryos to PAHs reduces the allocation of cells to the embryonic and placental lineages by inducing apoptosis in a Bax-dependent manner, thus compromising the developmental potential of exposed embryos.