The “39-Week Rule” was adopted by the American College of Obstetricians and Gynecologists
(ACOG) in 2009 to eliminate non-medically indicated (elective) deliveries prior to
39 weeks in an effort to improve neonatal outcomes.
Our primary objective was to quantify the effect of this policy change on adverse
neonatal outcomes among a cohort of term births in South Carolina.
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 admission to a Neonatal Intensive Care Unit. Our secondary outcomes were respiratory
morbidities (including respiratory distress syndrome and transient tachypnea of the
newborn), hypoxic–ischemic encephalopathy, seizure, sepsis, birth injuries, hyperbilirubinemia,
hypoglycemia, and feeding difficulties. Propensity score analysis was used to control
for maternal age, Body Mass Index, race, gestational hypertension, infection, placental
abruption, and gestational and pre-gestational diabetes. After stratification by propensity
score, the Cochran-Mantel-Haenszel test was used to compare groups.
620,121 infants were liveborn at term during the two study periods. After implementation
of the 39-week rule, there was a significant reduction in early-term deliveries. In
adjusted analyses, Neonatal Intensive Care Unit admission was significantly more common
in the post-implementation period. Respiratory morbidities were also significantly
more common post-implementation. In contrast, there were significant reductions in
birth injuries and hyperbilirubinemia in the post-implementation period.
Implementation of the 39-week rule was associated temporally with an increase in adverse
neonatal outcomes. The outcomes intended to be reduced by the 39-week rule, including
Neonatal Intensive Care Unit admission and respiratory morbidity, appear to have increased
in incidence despite adherence to the proposed guidelines.