Impact of the “39-week Rule” on Adverse Pregnancy Outcomes: A Statewide Analysis

Published:January 25, 2023DOI:



      The “39-week rule,” adopted by the American College of Obstetricians and Gynecologists (ACOG) circa 2009, discouraged routine elective induction of labor in early-term gestations (37w0d-38w6d) to decrease the risk of adverse neonatal outcomes. However, little research exists regarding any unintended adverse pregnancy outcomes associated with this policy shift.


      Our primary objective was to quantify the difference in incidence of adverse pregnancy outcomes pre- and post-implementation of this rule.

      Study Design

      De-identified data from all births in the state of South Carolina from 2000-2008 (prior to the 39-week rule) and 2013-2017 (after statewide implementation and enforcement of the rule) were obtained from the South Carolina Revenue and Fiscal Affairs Office. Demographic data and ICD9/10 codes were obtained for each birth. Our primary outcome was the incidence of any of the following adverse pregnancy outcomes: cesarean delivery, hypertensive disorders, chorioamnionitis, postpartum hemorrhage, high degree lacerations, placental abruption, and ICU admission. Propensity score analysis was used to control for age, body mass index, and race. After stratification by propensity score, the Cochran-Mantel-Haenszel test was used to compare the pre-rule and post-rule groups.


      A total of 633,985 births were eligible for inclusion; 412,632 from 2000-2008, and 221,353 from 2013-2017. There was a significant increase in the primary outcome between the pre- and post-rule periods (39.94% pre vs 42.76% post, p < 0.01). The incidence of all hypertensive disorders was significantly increased in the post-rule period compared to the pre-rule period (7.75% pre vs 10.1% post, p < 0.01). The incidence of chorioamnionitis and cesarean delivery rates also increased between pre- and post-rule periods (1.45% pre vs 1.92% post, p value < 0.01; 29.6% pre vs 31.82% post, p value < 0.01, respectively).


      There was a significant increase in the primary outcome following implementation of the 39-week rule. While the policy shift was driven by a desire to decrease adverse neonatal outcomes, aggregate benefit was not seen for pregnancy outcomes.


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