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A commentary on Practice Bulletin Number 146 by the Editor-in-Chief of Contemporary OB/GYN.
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
By Charles J. Lockwood, MD, MHCM
Dr. Lockwood is Senior Vice President, USF Health and Dean, Morsani College of Medicine, University of South Florida, Tampa. He is also the Editor-in-Chief of Contemporary OB/GYN.
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.
A Cochrane review found no difference between nonstress testing (NSTs) and biophysical profiles (BPP), though the latter may be associated with a higher cesarean delivery rate, albeit based on limited numbers of patients evaluated. There is limited evidence suggesting that twice-weekly testing might be superior to once-weekly testing in postterm gestations, but no firm recommendation is made. Given the link between oligohydramnios and postterm pregnancies and the former’s association with increased perinatal morbidity and mortality, ACOG opines that ultrasonographic assessment of amniotic fluid volume to detect oligohydramnios is warranted. The latter studies should use the deepest vertical pocket of amniotic fluid of 2 cm or less as the appropriate diagnostic criteria. Thus, the use of either BPP or a modified BPP (NST plus amniotic fluid assessment) twice weekly beginning at or beyond 41 0/7 weeks seems warranted.
A recent Cochrane registry report suggests that induction of labor at 41 completed weeks’ gestation is associated with fewer perinatal deaths, risk ratio (RR) of 0.31 (95% CI: 0.12 to 0.88) and significantly fewer cesarean deliveries (RR 0.89; 95% CI: 0.81 to 0.97) compared with expectant management.3 The number needed to treat to prevent one perinatal death was 410 (95% CI: 322 to 1492). Other benefits of induction include fewer cases of meconium aspiration syndrome. ACOG concludes that “Induction of labor between 41 0/7 and 42 0/7 weeks can be considered” and “Induction of labor after 42 0/7 weeks and by 42 6/7 weeks of gestation is recommended, given evidence of an increase in perinatal morbidity and mortality.”
This Practice Bulletin provides useful background data that should be used by obstetrical practices and hospitals to develop guidelines for the reduction of perinatal morbidity and mortality attendant postterm pregnancies.
1. American College of Obstetricians and Gynecologists. Practice bulletin no. 146: Management of late-term and postterm pregnancies. Obstet Gynecol. 2014;124(2 Pt 1):390-6. doi: 10.1097/01.AOG.0000452744.06088.48.
2. Caughey AB, Musci TJ. Complications of term pregnancies beyond 37 weeks of gestation. Obstet Gynecol. 2004;103(1):57-62.
3. Gülmezoglu AM, Crowther CA, Middleton P, Heatley E. Induction of labour for improving birth outcomes for women at or beyond term. Cochrane Database Syst Rev. 2012 Jun 13;6:CD004945. doi: 10.1002/14651858.CD004945.pub3.
ACOG Abstract References
1. Spong CY. Defining “term” pregnancy: recommendations from the Defining “Term” Pregnancy Workgroup. JAMA 2013;309:2445-6. (Level III)
2. Martin JA, Hamilton BE, Osterman MJ, Curtin SC, Mathews TJ. Births: final data for 2012. Natl Vital Stat Rep 2013:62(9):1-27. (Level II-3)