Perinatal Outcomes

The risk of adverse outcomes is greater for neonates delivered in the early-term period (37 0/7–38 6/7 weeks of gestation) compared with neonates delivered at 39 weeks of gestation Box 2. Because pulmonary development continues well into early childhood, respiratory morbidity is relatively common in neonates delivered in the early-term period. 9 A retrospective cohort study by the Consortium on Safe Labor, which included 233,844 births, found that among all infants delivered at 37 weeks of gestation, regardless of indication, there were higher rates of respiratory failure (adjusted odds ratio [OR], 2.8; 95% CI, 2.0–3.9) and ventilator use (adjusted OR, 2.8; 95% CI, 2.3–3.4) compared with infants delivered at 39 weeks of gestation 10. In addition, higher rates of respiratory distress syndrome, transient tachypnea of the newborn, pneumonia, and surfactant and oscillator use were reported for infants delivered at 37 weeks of gestation compared with those delivered at 39 weeks of gestation. Slightly higher rates of respiratory failure (adjusted OR, 1.4; 95% CI, 1.0–1.9) and ventilator use (adjusted OR, 1.2; 95% CI, 1.0–1.5) were reported for infants delivered at 38 weeks of gestation versus 39 weeks of gestation; however, the differences did not reach statistical significance and there was no commonly reported difference in any other measure of respiratory morbidity between these two groups 10.

In a secondary analysis of data from the Eunice Kennedy Shriver NICHD, neonates delivered during the early-term period by cesarean delivery, in the absence of indications for delivery, were associated with a higher risk of a composite outcome of neonatal respiratory and nonrespiratory morbidities compared with neonates delivered at 39 weeks of gestation 4. Of these nonmedically indicated deliveries, 35.8% were performed before 39 weeks of gestation. The rate of composite morbidity was higher for neonates delivered at 37 weeks of gestation (adjusted OR, 2.1; 95% CI, 1.7–2.5) and at 38 weeks of gestation (adjusted OR, 1.5; 95% CI, 1.3–1.7) compared with neonates delivered at 39 weeks of gestation. In addition, the morbidity for neonates delivered at 38 4/7–38 6/7 weeks of gestation remained significantly increased (relative risk, 1.21; 95% CI, 1.04–1.40). These findings suggest that scheduled cesarean delivery even a day before 39 weeks of gestation should be avoided.

In a large cohort of planned term deliveries (defined as deliveries not initiated by labor or ruptured membranes) during a 3-month period in 27 hospitals across the United States, neonatal intensive care unit (NICU) admission rates were higher among neonates delivered in the early-term period 2. A comparison of NICU admission rates for neonates delivered at 37 weeks of gestation or 38 weeks of gestation with those for neonates delivered at 39 weeks of gestation revealed that 31% of 17,794 deliveries had no medical indication. Admission to the NICU, which can be dependent on a variety of factors, was required for 17.8% of infants delivered without medical indication at 37 weeks of gestation and for 8% delivered without medical indication at 38 weeks of gestation, compared with 4.6% of infants delivered at 39 weeks of gestation or beyond ( P <.001 for deliveries at 38 weeks of gestation and 39 weeks of gestation).

Another large study found that although the rates of meconium aspiration were lower among neonates delivered at 37 weeks of gestation (adjusted OR, 0.62; 95% CI, 0.52–0.74) and 38 weeks of gestation (adjusted OR, 0.70; 95% CI, 0.62–0.79) compared with neonates delivered at 39 weeks of gestation, the rates of hyaline membrane disease were higher at 37 weeks of gestation (adjusted OR, 3.12; 95% CI, 2.90–3.38) and 38 weeks of gestation (adjusted OR, 1.30; 95% CI, 1.19–1.43) 11. When these two etiologies of pulmonary disease were examined as the combined metric of need for neonatal ventilation, the rates of disease were increased at 37 weeks of gestation (adjusted OR, 2.02; 95% CI, 1.88–2.18) and 38 weeks of gestation (adjusted OR, 1.15; 95% CI, 1.08–1.23). Additionally, in this study, the risk of a 5-minute Apgar score less than 7 decreased from 1.01% at 37 weeks of gestation to 0.69% at 38 weeks of gestation and 0.61% at 39 weeks of gestation ( P <.001).

Mortality rates are also higher among neonates and infants delivered during the early-term period compared with those delivered at full term 12. Using 39 weeks of gestation as the reference group, the relative risk of neonatal mortality is 2.3 (95% CI, 2.1–2.6) at 37 weeks of gestation and 1.4 (95% CI, 1.3–1.5) at 38 weeks of gestation Table 1. Mortality rates are also significantly higher among infants delivered at 37 weeks of gestation and 38 weeks of gestation compared with those delivered at 39 weeks of gestation Table 1. These increased mortality rates need to be balanced against the ongoing risk of stillbirth from week to week in an early-term pregnancy. In a study that compared the risk of neonatal mortality at a given week of gestation to the risk of expectant management, including stillbirth and neonatal mortality at the next week of gestation, there was an increased risk of mortality from delivery at 37 weeks of gestation (14.4 per 10,000 live births) compared with expectant management up to 38 weeks of gestation (12.6 per 10,000 live births, P <.05) 13. At 38 weeks of gestation, the risk of mortality was 10.5 per 10,000 live births compared with 11.6 per 10,000 live births from expectant management up to 39 weeks of gestation. This risk difference of 1.1 per 10,000 pregnancies reached statistical significance (95% CI, 0.03–2.18 per 10,000 deliveries), but would require 9,042 deliveries at 38 weeks of gestation to prevent one death.

Adverse Long-Term Infant Outcomes

In addition to immediate adverse perinatal outcomes, multiple studies have shown increased rates of adverse long-term infant outcomes associated with late-preterm and early-term delivery compared with full-term delivery. Studies have reported that compared with children born full term, children born late preterm and early term experience additional long-term adverse consequences including increased hospitalizations up to age 18 14 15, slower neurologic development 16 17 18, worse cognitive performance 19, more school-related problems, and poorer academic achievement 20 21. A recent systematic review found that late-preterm and early-term children have lower performance scores across a range of cognitive and educational measures compared with their full-term peers 22. Further research is needed to better understand if these differences are primarily based on gestational age at delivery versus the medical indications for early delivery 23.

Fetal Lung Maturity

The previously discussed literature suggests that the rate of respiratory morbidity remains higher among neonates delivered during the late-preterm and early-term periods when compared with neonates delivered at 39 weeks of gestation. However, because nonrespiratory morbidities also are increased in early-term deliveries, documentation of fetal pulmonary maturity does not justify an early nonmedically indicated delivery. A retrospective cohort study of 459 neonates delivered at 36 0/7 weeks of gestation up to 38 6/7 weeks of gestation after documented fetal lung maturity evaluated a composite outcome of respiratory and nonrespiratory complications. The researchers found that the incidence of the composite outcome decreased with increasing gestational age ( P for trend <.001): 9.2% (CI=5.9–14.1%) at 36 weeks of gestation, 3.2% (CI=1.5–6.8%) at 37 weeks of gestation, 5.2% (CI=2.0–12.6%) at 38 weeks of gestation, and 2.5% (CI=2.2–2.8%) at 39–40 weeks of gestation 24. In addition, a secondary analysis of an observational study from the Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network that monitored births from 115,502 women in 25 hospitals in the United States from 2008 to 2011 showed that even with confirmed pulmonary maturity, early-term birth in the absence of medical or obstetric indications is associated with worse neonatal respiratory and other neonatal outcomes compared with full-term birth 25. Thus, although fetal lung maturity testing may help identify fetuses at risk of respiratory distress syndrome, mature fetal pulmonary test results do not reliably predict all potential neonatal respiratory and other adverse outcomes and should not be used to justify a delivery in the absence of other indications.

The role of amniocentesis in determining fetal pulmonary maturity was discussed at the 2011 Eunice Kennedy Shriver NICHD and SMFM medicine workshop titled “Timing of Indicated Late-Preterm and Early-Term Birth” 26. The consensus was that if significant maternal or fetal risk warrants delivery, amniocentesis does not provide additional aid in guiding management. The converse also is thought to be true: If delivery could be delayed awaiting pulmonary maturity, then the indication is less urgent, and prompt delivery is not likely indicated. As mentioned previously, documentation of fetal pulmonary maturity alone does not necessarily indicate that other fetal physiologic processes are adequately developed. For this reason, amniocentesis for fetal lung maturity is not recommended to guide timing of delivery, even in suboptimally dated pregnancies 27.

Prevention of Nonmedically Indicated Early-Term Deliveries

Implementation of a policy to decrease the rate of nonmedically indicated deliveries before 39 0/7 weeks of gestation has been found to decrease the number of these deliveries and, as a result, improve overall neonatal outcomes. A recent study examined the implementation of three approaches to this issue: 1) a hard-stop policy, which prohibited nonmedically indicated deliveries at the hospital level; 2) a soft-stop policy, in which health care providers agreed not to perform nonmedically indicated deliveries before 39 weeks of gestation; and 3) an education program that informed health care providers about the risks associated with delivery before 39 weeks of gestation. Overall, these approaches contributed to a greater than 50% reduction in the rate of nonmedically indicated early-term deliveries, regardless of the policy used 28. However, the reduction was the greatest in the hard-stop policy group, with a reduction from 8.2% to 1.7% ( P =.007). The reduction was slightly less in the soft-stop policy group, with a reduction from 8.4% to 3.3% ( P =.025), and the least in the educational approach group, with a reduction from 10.9% to 6.0% ( P =.135), which was not statistically significant.

In a parallel effort, the Ohio Perinatal Quality Collaborative chose to focus on the reduction of nonmedically indicated deliveries at 36 0/7–38 6/7 weeks of gestation 29. Twenty hospitals in Ohio were enrolled in the study, and a range of approaches were provided to reduce nonmedically indicated deliveries, including improved determination of gestational age, use of ACOG's and SMFM's criteria for indication for delivery, education of patients and health care providers regarding these indications and the risks of a nonmedically indicated delivery before 39 weeks of gestation, and measurement of the outcome of a scheduled delivery without a documented indication. The researchers reported a reduction in the rate of nonmedically indicated deliveries at 36 0/7–38 6/7 weeks of gestation from 13% to 8% ( P =.003).

In South Carolina, there was a 4.7% decrease in late-preterm birth from 2011 to 2012 after the South Carolina Birth Outcomes Initiative instituted a hard-stop policy to prevent nonmedically indicated early-term deliveries in South Carolina. This collaboration between state health departments, hospitals, and other stakeholders led to an almost 50% reduction in nonmedically indicated early-term deliveries in South Carolina 30.

In Oregon, implementation of a hard-stop policy limiting early elective deliveries led to a reduction in elective inductions from 4.0% to 2.5% ( P <.001) and in elective early-term cesarean deliveries from 3.4% to 2.1% ( P <.001) before 39 weeks of gestation with no change in neonatal intensive care unit admission, stillbirth, or assisted ventilation 31.

A multistate quality improvement program, the Big 5 State Prematurity Initiative, included 26 hospitals from the five most populous states focused on reducing singleton elective deliveries before 39 weeks of gestation and showed that implementation of a comprehensive rapid-cycle change approach was effective in decreasing the rate of elective early-term deliveries from 27.8% to 4.8%, an 83% decrease within 1 year 32.

As states have effectively reduced early elective delivery, multiple studies using national population level data have shown that even as the gestational age at term has increased in response to efforts to reduce early elective delivery, these efforts have not adversely affected stillbirth rates nationally or even in states with the greatest reductions in early elective delivery 3 23 32 33 34 35. A single center study did report that after implementation of a hard-stop policy they reduced 37–38 weeks of gestation deliveries and reduced the rate of NICU admissions for neonates delivered at term, but also reported an increase in stillbirth rates at 37 weeks of gestation and 38 weeks of gestation, from 2.5 per 10,000 births to 9.1 per 10,000 births ( P =.03), although the absolute risk was small 36. A sequential ecological study of partial state data also reported an increase in term stillbirth across a 7-year period between 2007 and 2013 37. However, other studies with considerably larger sample sizes and population-based data have shown either a decrease in stillbirth 3 or no statistically significant change 32 33 34, and no association with increasing gestational age at term and stillbirth 23. In an analysis of 3.5 million births in the United States using state-level birth certificate and fetal death data from 2005 to 2011, early-term births decreased from 31.8% to 28.5%, with no increase in overall stillbirth risk at term observed (123/1,000 term still birth rate to 130/1,000 term still birth rate: P =.189) 34. In another analysis comparing births in the United States between 2006 to 2012, the stillbirth rate across preterm and term gestational ages remained unchanged at 6.05 per 1,000 despite a 10–16% reduction in births at 34–38 weeks of gestation and a 17% increase in births at 39 weeks of gestation 35.

These programs demonstrate that a reduction in nonmedically indicated early-term and late-preterm deliveries can be achieved. Studies clearly have shown short-term and long-term outcomes are improved for infants born at full term (39 0/7–40 6/7 weeks of gestation) versus late preterm (34 0/7–36 6/7 weeks of gestation) or early term (37 0/7–38 6/7 weeks of gestation). Importantly, multiple studies using national population level data have shown that even as the gestational age at term has increased in response to efforts to reduce early elective delivery, these efforts have not adversely affected stillbirth rates nationally or even in states with the greatest reductions in early elective delivery. Nonmedically indicated early delivery before 39 weeks of gestation and induction of labor or cervical ripening before 39 weeks of gestation should be avoided, given short-term and long-term adverse outcomes for the neonate. However, more research is necessary to further characterize pregnancies at risk of in utero morbidity or mortality and optimal timing of medically indicated early delivery.