Committee on Practice Bulletins—Obstetrics
ACOG Practice Bulletin Number 146: Management of Late-Term and Postterm Pregnancies, August 2014. Obstet Gynecol. 2014;124:390-396. Full text of ACOG Practice Bulletins is available to ACOG members at www.acog.org/Resources-And-Publications/Practice-Bulletins/Committee-on-Practice-Bulletins-Obstetrics/Management-of-Late-Term-and-Postterm-Pregnancies
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 (1). In 2011, the overall incidence of postterm pregnancy in the United States was 5.5% (2). 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 post-term 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.
Used with permission. Copyright the American College of Obstetricians and Gynecologists.
Commentary: Toward guidelines for reducing morbidity, mortality
The American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin: Management of Late-Term and Postterm Pregnancies (No. 146, August 2014) reviews the epidemiology and management of such pregnancies.1 Late-term gestation is defined as one occurring between 41 0/7 and 41 6/7 weeks, while postterm gestations extend to 42 0/7 weeks and beyond. In contrast, preterm pregnancies are less than 37 0/7 weeks’ gestation, early term gestations are between 37 0/7 weeks and 38 6/7 weeks, and full term occurs between 39 0/7 weeks and 40 6/7 weeks. The risk of stillbirth increases beyond 41 weeks.2 Additional fetal risks of postterm pregnancies include macrosomia, which increases the likelihood of operative vaginal deliveries, cesarean deliveries and shoulder dystocia, as well as neonatal seizures, meconium aspiration syndrome, and low 5-minute Apgar scores. Oligohydramnios is more common in postterm pregnancies and has been associated with cord compression, fetal heart rate abnormalities, meconium-stained amniotic fluid, and fetal acidosis. Maternal risks are generally those associated with macrosomia and related dysfunctional labors, including severe perineal lacerations, infection, and postpartum hemorrhage.
Two strategies are recommended to reduce the diagnosis of postterm and late-term gestations: 1) accurate dating using firm clinical criteria (eg, known ovulation date or early ultrasound, the latter of which can reduce the rate of postterm pregnancy); and 2) membrane sweeping when there are no contraindications (eg, placenta previa and perhaps group B Streptococci carriage).
Definitive recommendations for fetal surveillance are hampered by the absence of randomized controlled trials demonstrating that antepartum fetal surveillance actually decreases perinatal morbidity or mortality in late-term and postterm gestations. Thus, ACOG suggests that based on epidemiological data linking advancing gestational age to stillbirth, antepartum fetal surveillance at or beyond 41 0/7 weeks “may be indicated.” There are also no definitive studies determining the optimal type or frequency of such testing.