In the past decade, the rate of preterm delivery in the United States has declined 11% from its peak of 12.8% in 2006.1 That decline reflects a variety of influences including reduction in higher-order multiple births due to more stringent embryo transfer policies, reductions in maternal smoking, increased access to maternity care, and increased use of 17 α-hydroxyprogesterone caproate in women with prior preterm birth. Moreover, given the recognition that neonatal mortality rates decrease from 4.8/1000 at 35 weeks to 1.7/1000 at 37 weeks, there has been a highly successful national effort to eliminate non-medically indicated “elective” preterm deliveries.2
Because neonatal mortality and morbidity rates nadir when delivery occurs at 39 to 40 weeks,2,3 the Joint Commission, American College of Obstetricians and Gynecologists, March of Dimes, and various states have also sought to reduce non-medically indicated deliveries occurring between 37 0/7 and 38 6/7 weeks’ gestation—elective early term deliveries.4-7 Critics of this strategy argue that the additional weeks spent in utero pose a countervailing risk of excess stillbirth, particularly if medically indicated deliveries are conflated with non-medically indicated deliveries. Others have challenged the dogma that elective early term deliveries actually increase neonatal morbidity and mortality.
A recent series of elegant epidemiological studies provides some reassurance concerning adherence to the so-called “39-week rule” and associated stillbirth rates, but also raise thorny questions about whether or not elective early term inductions truly increase neonatal morbidity and mortality.
Is there a connection?
This question was addressed by Little and associates, who conducted a retrospective descriptive analysis of the relationship between declining early term deliveries among singleton gestations and term (>37 week) stillbirth rates from 2005 to 2011 based on national birth and fetal death certificate data.8 These rates were also calculated for each state, and for both low- and high-risk women. The authors sought to determine whether states with greater reductions in early term deliveries had higher term stillbirth rates.
As expected, they found an overall 10.3% relative decline in early term deliveries across the United States from 1,123,467 of 3,533,233 (31.8%) births in 2005 to 978,294 of 3,429,172 (28.5%) births in 2011. They noted wide state variability: from a 25.5% decline in Ohio to a 3.9% increase in Arkansas. During the same period there was no statistically significant change in overall term stillbirth rates (123/100,000 vs 130/100,000; P=0.189). Moreover, among low-risk patients, stillbirth rates were negligibly different between 2005 and 2011 (105/100,000 vs 110/100,000; P=0.17). At the state level, there was also no correlation between overall reductions in early term deliveries and increases in term stillbirth rates.
These authors did note that the incidence of gestational and pregestational diabetes had increased from 3.5% to 5.2% during the study period potentially due to better coding or an increasing frequency of older obese gravidas. As with the overall population, the rate of early term deliveries among diabetic patients also declined during this period from 42.4% to 36.7% but stillbirth rates among diabetics rose 25% from 238/100,000 to 300/100,000 (P=0.01). The authors suggest this increase may reflect clinicians misapplying early-term delivery policies designed for low-risk women to high-risk women.