When a firm estimated date of delivery (EDD) is established early in pregnancy, providers can anticipate that most pregnancies will result in spontaneous delivery at term. The incidence of delivery at or beyond 42 weeks is approximately 3:1000 pregnancies (a decrease of 50% over the last decade). Under some circumstances, however, pregnancy may continue beyond 42 weeks, requiring assessment and management as a postterm pregnancy. The cause of prolonged gestation is not well understood, but patients with one postterm delivery have a 50% likelihood of subsequent postterm delivery.