Smoking, sex of the offspring, and risk of placental abruption, placenta previa, and preeclampsia: a population-based cohort study.

BACKGROUND: : Placental abruption, placenta previa, and preeclampsia are serious pregnancy complications with an increased risk of perinatal death. Smoking during pregnancy is associated with increased risk of abruption and placenta previa, and it reduces the risk of preeclampsia. We examined the association between mothers' smoking habits during pregnancy, taking the sex of the offspring into consideration, and the risk and prognosis of placental abruption, placenta previa, and preeclampsia

METHODS: : We conducted the study in the County of North Jutland, Denmark. Using the 10-digit personal identification number given to every Danish citizen at birth, we linked data from the Danish Medical Birth Registry, including information on mother and child, to data from the Pharmaco-Epidemiological Prescription Database with data on all reimbursed prescriptions to use selected drugs as a proxy measure for some maternal diseases, and data from the Regional Hospital Discharge Registry, including the discharge diagnoses. Among 47,932 singleton births we included only births for which we had information about the mothers' smoking habits, leaving 46,313 births for analysis.

RESULTS: : Smoking was associated with the risk of placental abruption (OR=1.99 (95% CI 1.72-2.30)) and placenta previa (OR=1.88 (95% CI 1.15-3.07)). Smoking was inversely associated with the risk of preeclampsia (OR=0.55 (95% CI 0.48-0.62)). After stratification for the sex of the offspring the risk estimate of smoking as risk factor for placenta previa decreased for male fetuses (OR=1.63 (95% CI 0.75-3.51)) and increased for female fetuses (OR=4.82 (95% CI 1.69-13.75)).

CONCLUSION: : Female fetuses are more vulnerable than male to the negative effect of maternal smoking on placenta previa.