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#Grand Rounds

Does Extending Pregnancy Beyond 39 weeks in Low-risk Pregnancies Incur Additional Risk?

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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

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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?
Guidance on How to Manage the Suboptimally Dated Pregnancy

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