Preconception Blood Pressure and Sex of the Baby: A Large Prospective Cohort Study in China.

A recent study suggested an increase in male births associated with maternal preconception high blood pressure. Our objective was to examine this association. Data were obtained from the China-US Collaborative Project for Neural Tube Defects Prevention, a large population-based cohort study. We included 44 399 singleton pregnancy to women who were registered before pregnancy in seven counties in southern China. Blood pressure was measured during registration by trained health care workers and other health-related information was recorded prospectively. We used log-binomial regression to evaluate the associations between preconception blood pressure and the risk of male delivery, adjusting for potential confounders. The study size had 99% power (α = 0.05) to detect an increase of 50% over the unexposed rate of 51.94% for male delivery. The prevalence of hypertension in the preconception study population was 4.61% (2045/44 399). The prevalence of male delivery was 51.10% for the hypertension group and 51.79% for the non-hypertension group. Compared with the non-hypertension group, the hypertension group did not show significantly increased chance for male delivery [adjusted risk ratio (RR) = 0.99, 95% confidence interval (CI): 0.94, 1.03]. Our results do not support an association between hypertension or higher blood pressure prior to pregnancy and increased likelihood of male delivery.