BACKGROUND AND PURPOSE:

• The ‘39-week rule’ has been instituted nationally to reduce elective deliveries <39 weeks
• Pilliod et al. (JAMA Pediatrics, 2019) assessed the impact of the 39-week rule on stillbirths and infant deaths

METHODS:

• Historical cohort study
• Participants
  • Singleton, nonanomalous births
  • Between 37w0d and 42w6d
• Data source: Birth certificates and infant death certificates
• Groups (prior and post 39-week rule adoption)
  • Preadoption period: Births between 2008 and 2009
  • Postadoption period: Births between 2011 and 2012
• Primary outcomes
  • Stillbirth
  • Infant death

RESULTS:

• Preadoption: 7,322,234 births | 49.0% girls and 51.0% boys
• Postadoption: 6,972,626 births | 49.1% girls and 50.9% boys
• Compared to the preadoption period, in the postadoption period, there was a
  • Decrease in the proportion of deliveries at 37 weeks: −0.06%
  • Decrease in proportion of deliveries at 38 weeks: −2.5%
  • Increase in the proportion of deliveries at 39 weeks: 6.8%
  • Increase in the proportion of deliveries 40 weeks: 0.2%
• Stillbirth rate increased in the in the postadoption cohort (P < 0.001)
  • Preadoption: 0.09%
  • Postadoption: 0.10%
  • 0.81 additional stillbirths per 10,000 pregnancies in preadoption group
• Infant death rate decreased in the postadoption period (P < 0.001)
  • Preadoption: 0.21%
  • Postadoption: 0.20%
  • 1.37 fewer infant deaths per 10,000 live births in the postadoption group | Greatest reduction at 39 to 40 weeks
• Overall mortality rate was not statistically different (P = .06)
  • Preadoption: 0.31%
  • Postadoption: 0.30%
• To account for other confounders, especially older gestational age at delivery following adoption, a counterfactual model suggests that up to 34.2% of the difference in mortality could be associated with the 39-week rule

CONCLUSION:

• Stillbirth rates increased following adoption of the 39-week rule, but infant death decreased, with an overall mortality remaining unchanged
• Authors recognize that this study (1) Cannot account for all temporal changes in perinatal mortality over this time period and that (2) morbidity was not analyzed
• The authors urge caution in interpreting the results of this study and suggest that

Additional investigations are warranted to examine the various contributions to the observed increased rates of stillbirth including the application of this policy and practice creep related to prolonging gestations at term among pregnancies with high-risk conditions warranting late preterm or early-term delivery

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Learn More – Primary Sources:

Association of Widespread Adoption of the 39-Week Rule With Overall Mortality Due to Stillbirth and Infant Death

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