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