Placenta previa, maternal smoking and recurrence risk.

In order to assess the risk of placenta previa among women who smoked during pregnancy and to study the recurrence risk of placenta previa, we analyzed data from the Swedish Medical Birth Registry. Among 1,825,998 infants of women delivered in 1973-1990, 5,683 had placenta previa registered. The overall incidence of placenta previa was 0.3%, the incidence in twin deliveries was also 0.3%. The recurrence rate of placenta previa was 2.4%, which is an eightfold increase compared with the rate of a placenta previa among all births. Maternal smoking was studied for births in 1983-1990 and appeared as an independent risk factor for placenta previa. A dose-response between the number of cigarettes smoked during pregnancy and the risk of having a placenta previa was indicated.