Human semen quality and the secondary sex ratio

Abstract

The aim of this study was to evaluate the association between semen quality and the secondary sex ratio (SSR), defined as the ratio of male to female live births. Our study cohort comprised 227 male partners who were enrolled prior to conception in Michigan and Texas between 2005 and 2009, and prospectively followed through delivery of a singleton birth. The male partners provided a baseline and a follow-up semen sample a month apart. Semen analysis was conducted to assess 27 parameters including five general characteristics, six sperm head measures, 14 morphology measures, and two sperm chromatin stability assay measures. Modified Poisson regression models with a robust error variance were used to estimate the relative risk (RR) and 95% confidence interval (95% CI) of a male birth for each semen parameter, after adjusting for potential confounders. Of the 27 semen parameters, only the percentage of bicephalic sperm was significantly associated with the SSR (2nd vs 1st quartile, RR, 0.65, 95% CI, 0.45–0.95, P = 0.03; 4th vs 1st quartile, RR, 0.61, 95% CI, 0.38–1.00, P < 0.05 before rounding to two decimal places), suggestive of a higher percentage of bicephalic sperm being associated with an excess of female births. Given the exploratory design of the present study, this preconception cohort study suggests no clear signal that human semen quality is associated with offspring sex determination.

The risk of secondary sex ratio imbalance and increased monozygotic twinning after blastocyst transfer: data from the Japan Environment and Children’s Study

“…Regarding association between SSR and parental stress, it is indicated that the variation in the SSR may result from alteration in the sex-selective preimplantation embryo loss [35]. As mechanisms affecting this alteration, sperm abnormality, reduced coitus and perturbations in the female reproductive tract caused by stress before preconception are considered [36, 37]. Similar reasons may affect the incidence of MZT.…”

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

“…However, the current evidence is conflicting with other studies demonstrating no association between ART and SSR, but they are limited by their small sample sizes (Altman and Bland, 1995; Luke et al , 2009; Al-Jaroudi et al , 2018). This is further reflected in studies looking at semen parameters and SSR, with even fewer patients included (Bae et al , 2017; Malo et al , 2017).…”

Revisiting the Trivers-Willard theory on birth sex ratio bias: Role of paternal condition in a Malagasy primate

“…Recently, environmental endocrine-disrupting chemicals, for example, perfluoroalkyl substances (PFAS), bisphenol (BPA) and pesticides, have been shown to affect parental hormones and the secondary sex ratio through changes in sperm morphology and motility [29–31]. When both parents are exposed to PFAS, BPA or other chemical substances, an excess of female births is observed that is significantly linked to only paternal chemical concentrations [32–34]. Thus, endocrine-disrupting chemicals have clear anti-androgenic activities, as demonstrated in most animal studies [35–37] and in adult humans [38–40].…”

“…Thus, endocrine-disrupting chemicals have clear anti-androgenic activities, as demonstrated in most animal studies [35–37] and in adult humans [38–40]. However, to determine whether the alterations of human sperm are correlated with low fertility and low sex ratio at birth, a direct relationship remains to be established between sperm quality and testosterone levels and a decrease in birth sex ratio [31, 34, 41].…”