BACKGROUND AND PURPOSE:

• When determining the optimal delivery week for low-risk pregnancies, large datasets are required to account for important but relatively rare complications such as stillbirths
• Efforts continue to prevent delivery in ‘early term’, between 37w0d and 38w6d
• ‘Full term’ is between 39w0d and 40w6d (ACOG)
• Vilchez et al. (American Journal of Perinatology, 2017) assessed the risk of expectant management at term and the optimal timing for delivery using a national birth dataset

METHODS:

• Retrospective, population-based cohort (CDC cohort, 2013)
• Study consisted of nonanomalous, singleton term deliveries ≥ 37w0d
  • Complications that could result in early delivery were excluded
• Primary outcomes were maternal/neonatal complications and stillbirth/infant death
• Researchers compared delivery vs expectant management cohorts
• Odds ratios of complications according to delivery plan at each gestational age were calculated using logistic regression

RESULTS:

• 8,994,796 deliveries in the US
  • 3,940,764 live births and 54,028 stillbirths
  • 3,199,246 deliveries available for analysis following inclusion/exclusion criteria
• Maternal complications during expectant management were lower at early term (1.3%) and became higher at ≥ 39 weeks (1.7%)
  • Relative risk [RR] 1.18 (95% CI 1.16–1.19; p < 0.001)
• Neonatal complications during expectant management were lower during early term (4.8%), and became higher at ≥39 weeks (5.5%)
  • RR 1.09 (95% CI 1.08–1.09; p < 0.001)
• Infant death rate distribution was U-shaped, with the nadir at 39 to 40 weeks’ gestation
• Perinatal mortality risk (stillbirth + infant death) in the expectant management group was lower during early term (17.37/10,000) and higher at ≥39 weeks (18.93/10,000); p = 0.010

CONCLUSION:

• This study confirms the use of the ’39 week rule’ in low-risk pregnancies
  • Complications during expectant management occurring while awaiting full term do not outweigh the benefits of better outcomes from reaching 39 weeks
  • Risks to mother and infant may increase after 39-40 weeks gestation
• Authors of this study call for further research, however RCTs may be difficult due to the large number of study subjects required

Learn More – Primary Sources:

Risk of Expectant Management and Optimal Timing of Delivery in Low-Risk Term Pregnancies: A Population-Based Study

Related ObG Topics:

Deliver Low Risk Patients at 39 Weeks to Prevent Hypertensive Complications?

Induction to Prevent Stillbirths for Age 35 and Older: Impact on Cesarean Rates?

ACOG Committee Opinion: The Suboptimally Dated Pregnancy