Main findings
To the best of our knowledge, this is the first study to elucidate the risk factors for placental abruption based on the data of a large cohort study conducted in Japan. Consistent with several studies, the present study demonstrated that history of placental abruption, ART pregnancy, smoking during pregnancy, chronic hypertension, and maternal age were the risk factors for placental abruption. We also found that compared to advanced maternal age, teenage maternal age was more strongly associated with placental abruption. The number of previous deliveries was not associated with the incidence of placental abruption.