A cesarean first birth increases the risks for placenta previa and placenta abruption in subsequent pregnancies. So does a short interpregnancy interval, according to a retrospective cohort study of almost 200,000 singleton pregnancies.

Researchers calculated that the risk for previa is increased 63% in a pregnancy after a cesarean, as opposed to a vaginal delivery. And a pregnancy after two C/S compared with two vaginal deliveries carries a relative risk for previa of 2.0 (95% CI; 1.3–3.0).

Similarly, the risk for abruption is 74% higher in a pregnancy after a C/S delivery than after a vaginal delivery, and a pregnancy after two C/S deliveries has a 30% higher risk for abruption than does a pregnancy following two vaginal deliveries.

Relative risks for previa and abruption associated with a pregnancy within a year of a C/S are 1.7 (95% CI; 0.9–3.1) and 1.5 (95% CI; 1.1–2.3), respectively.

Getahun D, Oyelese Y, Salihu HM, et al. Previous cesarean delivery and risks of placenta previa and placental abruption. Obstet Gynecol. 2006;107:771-778.