Fecundity and sex ratio of offspring in an infertile cohort

Human semen quality and the secondary sex ratio

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 (2^ndvs 1^st quartile, RR, 0.65, 95% CI, 0.45–0.95, P = 0.03; 4^thvs 1^st 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.

Agency in Fertility Decisions in Western Europe During the Demographic Transition: A Comparative Perspective

We use a set of linked reproductive histories taken from Sweden, the Netherlands, and Spain for the period 1871–1960 to address key issues regarding how reproductive change was linked specifically to mortality and survivorship and more generally to individual agency. Using event-history analysis, this study investigates how the propensity to have additional children was influenced by the number of surviving offspring when reproductive decisions were made. The results suggest that couples were continuously regulating their fertility to achieve reproductive goals. Families experiencing child fatalities show significant increases in the hazard of additional births. In addition, the sex composition of the surviving sibset also appears to have influenced reproductive decisions in a significant but changing way. The findings offer strong proof of active decision-making during the demographic transition and provide an important contribution to the literature on the role of mortality for reproductive change.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Preconception stress and the secondary sex ratio: a prospective cohort study

OBJECTIVE

To study the association between salivary stress biomarkers and the secondary sex ratio.

DESIGN

Prospective, longitudinal cohort study.

SETTING

Community setting in the United Kingdom.

PATIENT(S)

On discontinuation of contraception for purposes of becoming pregnant, 338 women aged 18-40 years with complete data (90%) were followed until pregnant or up to six menstrual cycles.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Secondary sex ratio.

RESULT(S)

Human chorionic gonadotropin pregnancies were detected in 207 (61%) women of whom 130 (63%) delivered singleton infants with available gender data. The adjusted odds ratio for a male birth was decreased for women in the highest quartile (AOR = 0.26; 95% confidence interval = 0.09, 0.74) of salivary cortisol relative to women in the lowest quartile during cycle 1. An inverse relation was observed between α-amylase and the 2° sex ratio, though not statistically significant.

CONCLUSION(S)

Our findings are consistent with a reversal in the 2° sex ratio with increasing preconception salivary cortisol concentrations. This relation suggests that activation of the hypothalamus-pituitary-adrenal axis may have implications in sex allocation and requires further study.

Sperm counts and sperm sex ratio in male infertility patients

In recent years, investigators have noted a trend toward a declining proportion of male births in many industrialized nations. While men bear the sex-determining chromosome, the role of the female partner as it pertains to fertilization or miscarriage may also alter the gender ratio. We attempted to determine a man's secondary sex ratio (F1 generation) by directly examining the sex chromosomes of his sperm. We examined our male infertility clinic database for all men who had undergone a semen fluorescence in situ hybridization (FISH). Patient demographic and semen parameters were recorded. Chi-squared analysis was used to compare gender ratios (Y chromosomes/total chromosomes). Multivariable logistic regression was used to predict the odds of possessing a Y-bearing sperm after accounting for demographic and semen parameters. A total of 185 men underwent sperm FISH. For the entire cohort, the proportion of Y chromosome-bearing sperm was 51.5%. Men with less than five million motile sperm had a significantly lower proportion of Y chromosome-bearing sperm (50.8%) compared to men with higher sperm counts (51.6%; P=0.02). After multivariable adjustment, a higher sperm concentration, total motile sperm count and semen volume significantly increased the odds of having a Y chromosome-bearing sperm (P<0.01). As a man's sperm production declines, so does the proportion of Y chromosome-bearing sperm. Thus, a man's reproductive potential may predict his ability to sire male offspring.