In the past decade, the rate of preterm delivery in the United States has declined 11% from its peak of 12.8% in 2006.
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.
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.
MacDorman and associates studied this issue using a different approach.9 They mined National Center for Health Statistics fetal death and live birth data for 2006 and 2012 to compute gestational age-specific stillbirth rates ≥ 20 weeks using 2 methods: 1) a “traditional” technique that measured the ratio of the number of stillbirths at a given gestational age divided by the number of live births plus stillbirths at that gestational age, x 1000; and 2) a “prospective” method that measured the ratio of stillbirths at a given gestational age divided by the number of live births plus stillbirths at that gestational age or greater, x 1000. The authors posited that the prospective method was superior because it gave a good approximation of the number of women still pregnant and thus at risk of subsequent stillbirth at a given gestational age.
They found that between 2006 and 2012, the percent distribution of live births at 34 to 38 weeks decreased by 10%–16%, while births at 39 weeks increased by 17%, consistent with efforts at reducing both elective preterm and early term deliveries. While the traditional method showed an increase in stillbirths at 34 to 36, 37, and 38 weeks, these rates were influenced by decreases in live births at those gestational ages. In contrast, there were no differences in prospective stillbirth rates at 21 to 42 weeks, leading the authors to conclude that “preventing non-medically indicated deliveries before 39 weeks of gestation did not increase the stillbirth rate at the national level.”
Taken together, the findings from these 2 studies provide some reassurance that efforts to reduce neonatal morbidity and mortality putatively caused by elective early term deliveries have not increased stillbirth rates.
But are elective early term deliveries clearly linked to excess neonatal morbidity and mortality? Salemi and associates addressed this question in a population-based retrospective cohort study of 675,302 singleton infants born alive at 37 to 44 weeks’ gestation from 2005 to 2009 in more than 125 birthing facilities in Florida.10 They excluded pregnancies with maternal medical or obstetrical complications, history of substance abuse, or neonatal congenital anomalies. Five subgroups were analyzed: 1) early (37-38 weeks) elective induction (4.9%); 2) early elective cesarean deliveries (8.2%); 3) early spontaneous deliveries (16.7%); 4) early medically indicated deliveries (3.4%); and 5) delivery at 39 to 40 weeks (60.7%), which served as the control group.
The primary outcomes were neonatal respiratory morbidity, sepsis, feeding difficulties, neonatal intensive care unit (NICU) admission, and infant mortality.
The authors found no statistically significant increase in neonatal mortality in the early term induction group; however, even with the large numbers of pregnancies studied, given the rarity of such deaths, such a linkage cannot be entirely excluded. They also found no differences in respiratory morbidity, sepsis, or NICU admission in the early elective versus 39 to 40 week control group, although the former did have more feeding difficulties (OR 1.18; 99%CI: 1.02–1.36). However, when examining differences between nulliparous women and multiparous women without prior cesarean deliveries undergoing early elective induction, the latter group’s infants displayed higher NICU admission rates (OR 1.23; 99%CI: 1.06–1.42), and feeding difficulties (OR 1.28; 99%CI: 1.06–1.55). By contrast, infants delivered by early elective cesarean experienced a 66% increase in respiratory morbidity, 51% more NICU admissions, and 36% higher rate of feeding abnormalities as well as an increased risk of sepsis (OR of 1.13; 99%CI: 1.01–1.29) compared to those delivered at 39 to 40 weeks. Here again the infants of multiparous women without prior cesarean deliveries fared worse than infants of nulliparous women.
These findings suggest that the extent of neonatal morbidity accruing early elective induction of nulliparous women may be less than previously suspected. However, such inductions increase neonatal morbidity among multiparas. Clearly, early cesarean deliveries are associated with excess morbidity in both maternal groups. The authors state that “issues that surround the timing and reasons for delivery initiation are complicated and each pregnancy unique. This study cautions against a general avoidance of all elective early-term deliveries.”
We can be reasonably reassured that national quality assurance efforts aimed at reducing elective early term deliveries have not resulted in a dramatic increase in term stillbirth rates. However, the magnitude of the neonatal risks of elective early term delivery in nulliparous women, who are at greatest risk for subsequent stillbirth and obstetrical complications, may have been exaggerated by earlier studies. Moreover, there are real concerns that in our zeal to reduce truly “elective” early term deliveries, patients with bona fide medical or obstetrical indications for such early deliveries may be experiencing inappropriate and potentially harmful pregnancy prolongation.
On balance, I believe that non-medically indicated early term deliveries should be discouraged but it falls to the obstetrician’s art to constantly assess whether a patient with a complicated pregnancy is better of delivered.
Dr Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South Florida, Tampa.
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