Practice bulletin no. 146: Management of late-term and postterm pregnancies.

Postterm pregnancy refers to a pregnancy that has reached or extended beyond 42 0/7 weeks of gestation from the last menstrual period (LMP), whereas a late-term pregnancy is defined as one that has reached between 41 0/7 weeks and 41 6/7 weeks of gestation (). In 2011, the overall incidence of postterm pregnancy in the United States was 5.5% (). The incidence of postterm pregnancies may vary by population, in part as a result of differences in regional management practices for pregnancies that go beyond the estimated date of delivery. Accurate determination of gestational age is essential to accurate diagnosis and appropriate management of late-term and postterm pregnancies. Antepartum fetal surveillance and induction of labor have been evaluated as strategies to decrease the risks of perinatal morbidity and mortality associated with late-term and postterm pregnancies. The purpose of this document is to review the current understanding of late-term and postterm pregnancies and provide guidelines for management that have been validated by appropriately conducted outcome-based research when available. Additional guidelines on the basis of consensus and expert opinion also are presented.