Impact of maternal smoking and secondhand smoke exposure during singleton pregnancy on placental abruption: analysis of a prospective cohort study (the Japan Environment and Children's Study).

Objectives: This study aimed to investigate the association and population-attributable fraction (PAF) of maternal smoking and secondhand smoke (SHS) exposure during pregnancy with placental abruption.

Design: Prospective cohort study.

Setting: 15 regional centres in Japan.