Abstract
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.