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Management of Late-Term and Postterm Pregnancy

Breanna Gawrys, DO
Diana Trang, DO
Whay Cheng, DO

American Family Physician. 2024;110(4):378-384.

Author disclosure: No relevant financial relationships.

This clinical content conforms to AAFP criteria for CME.

Postterm pregnancy is defined as a pregnancy that has reached 42 weeks' gestation and late-term pregnancy includes 41 weeks' and 0 days' to 41 weeks' and 6 days' gestation. Accurate first-trimester dating is essential for determining or verifying gestational age. Ideal management of late-term and postterm pregnancy involves shared decision-making on timing of planned delivery based on risks and preferences. Starting at 42 weeks' gestation, the risks of fetal mortality, admission to the neonatal intensive care unit, and stillbirth increase exponentially. Induction of labor at 41 weeks' gestation reduces perinatal mortality and stillbirth compared with expectant management or induction starting at 42 weeks' gestation. Recent studies have shown a decrease in cesarean deliveries and hypertensive disorders of pregnancy with induction of labor in nulliparous, low-risk pregnancies beginning at 39 weeks' gestation. Induction of labor before 42 weeks' gestation decreases the risk of stillbirth, perinatal mortality, and cesarean delivery compared with expectant management. The American College of Obstetricians and Gynecologists suggests considering an elective induction of labor in low-risk, nulliparous patients starting at 39 weeks' and 0 days' gestation and recommends induction of labor in all patients by 42 weeks' gestation. The American College of Obstetricians and Gynecologists recommends antepartum monitoring of pregnancies beginning at 41 weeks' gestation to mitigate the risks of perinatal morbidity and mortality.

Postterm pregnancy starts at 42 weeks' and 0 days' gestation and late-term pregnancy includes 41 weeks' and 0 days' to 41 weeks' and 6 days' gestation.1 Gestational age is established using the first day of the last menstrual period (LMP) and confirmed by first-trimester ultrasonography or by the established gestational age from assisted reproductive technology.1–3 Recent data show that 0.25% of all pregnancies continue to at least 42 weeks' gestation, a notable decrease from 5.5% reported in 2014.1,4 Table 1 lists risk factors for prolonged gestation.1,2

WHAT'S NEW ON THIS TOPIC

Late-Term and Postterm Pregnancy
Recent data show that 0.25% of all pregnancies continue to at least 42 weeks' gestation, a notable decrease from 5.5% reported in 2014.
A 2019 systematic review and meta-analysis found a nearly 30-fold increased risk of stillbirth with increased gestational age across term gestation, from 0.11 per 1,000 births at 37 weeks' gestation to 3.18 per 1,000 births at 42 weeks' gestation.
A multicenter trial found that labor induction of low-risk, nulliparous patients at 39 weeks' gestation produced no significant difference in composite adverse perinatal outcomes, but it significantly lowered the frequency of cesarean deliveries (number needed to treat = 28) and hypertensive disorders of pregnancy (number needed to treat = 20).

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating Comments
Labor induction should be considered beginning at 41 weeks' gestation based on the reduction of perinatal mortality and stillbirth.1,9–11,16–18 B Limited evidence from multiple randomized controlled trials, expert guidelines, and Cochrane reviews
Labor induction at 42 weeks' gestation is recommended for reduction of perinatal morbidity and mortality compared with expectant management.1,8,10,16,18 A Consistent evidence from expert guidelines and systematic reviews
Elective induction of labor may be offered to low-risk, nulliparous patients at 39 weeks' gestation and has been shown to reduce the rate of cesarean deliveries (NNT = 28), without an increased risk of maternal or neonatal harm.20–22 B Evidence of improved patient outcomes in a large randomized controlled trial; ACOG practice guideline and Society for Maternal-Fetal Medicine committee recommendation
Antepartum fetal surveillance performed once or twice weekly is recommended at 41 weeks' gestation despite limited supporting evidence.1,23 C ACOG expert committee statement
Membrane sweeping at 38 weeks' gestation or later may be considered to encourage spontaneous labor, with an NNT of 8, to decrease the risk of late-term and postterm pregnancies.1,26,27 B Cochrane review of lower-quality studies, systematic reviews, expert guidelines

ACOG = American College of Obstetricians and Gynecologists; NNT = number needed to treat.

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

BREANNA GAWRYS, DO, FAAFP, FACLM, DipABLM, is associate program director of the David Grant Medical Center Family Medicine Residency, Travis Air Force Base, Calif.; an associate professor of family medicine at the Uniformed Services University of the Health Sciences, Bethesda, Md.; and an associate professor of family medicine at the University of California Davis School of Medicine.

DIANA TRANG, DO, is core faculty at the David Grant Medical Center Family Medicine Residency, an assistant professor of family medicine at the Uniformed Services University of the Health Sciences, and an assistant professor of family medicine at the University of California Davis School of Medicine.

WHAY CHENG, DO, is core faculty at the David Grant Medical Center Family Medicine Residency, an assistant professor of family medicine at the Uniformed Services University of the Health Sciences, and an assistant professor of family medicine at the University of California Davis School of Medicine.

Address correspondence to Breanna Gawrys, DO, at Breanna.L.Gawrys.mil@health.mil.

Author disclosure: No relevant financial relationships.

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