Which of the following is NOT a risk factor for placental abruption?

Placental abruption, or the premature separation of the placenta from the uterus, has several established risk factors, including smoking, multiple gestations, and gestational hypertension.

Smoking is well-documented as a risk factor because it can affect blood flow and lead to various complications in pregnancy. Multiple gestations increase the risk of abruption due to the increased uterine distension and other physiological changes that occur with carrying more than one fetus. Gestational hypertension, which involves high blood pressure developing during pregnancy, is another recognized risk factor due to increased stress on the placental attachment.

In contrast, a previous cesarean delivery is not considered a classic risk factor for placental abruption. While there are some associations noted with uterine surgery and other complications later in pregnancy, the direct link between a past cesarean section and the likelihood of placental abruption is not as clear as it is with the other mentioned factors. This lack of a significant association is what distinguishes it as not being a recognized risk factor compared to the others.