Placenta praevia and male sex at birth: results from a population-based study.

This study examined the relationship between male sex at birth and placenta praevia in 433031 mother/infant dyads (linked by a common institutional code and hospital admission number) in the Canadian province of Quebec, during the fiscal years of 1991/92-1995/96. The male-to-female ratio among pregnancies with and without placenta praevia was calculated and compared. The male-to-female ratio at birth was higher in pregnancies complicated by a placenta praevia (1.19) than in those without it (1.04; P < 0.02). This increased ratio persisted after accounting separately for the potential confounding and/or modifying effects of maternal age, infant birthweight and gestational age by stratified and multiple logistic regression analyses. We conclude that pregnant women with male babies carry a higher risk of placenta praevia.