What about uncommon adverse outcomes compared at 39 vs 41 weeks?
Due to the study’s sample size, ARRIVE investigators could not ascertain if uncommon adverse outcomes (maternal admission to intensive care unit or neonatal seizure) are significantly more common at 40 and 41 weeks, than at 39 weeks.
To address the issue of uncommon adverse outcomes, Chen and colleagues analyzed the US Vital Statistics datasets to compare composite maternal and neonatal morbidity among low-risk nulliparous women with nonanomalous singleton gestations who labored at 39 to 41 weeks.5 The primary outcome was composite neonatal morbidity that included Apgar score < 5 at 5 minutes, assisted ventilation longer than 6 hours, seizure, or neonatal mortality. The secondary outcome was composite maternal morbidity that included intensive care unit admission, blood transfusion, uterine rupture, or unplanned hysterectomy.
The investigators found that from 2011–2015, among 19.8 million live births in the United States, there were 3.3 million live births among low-risk nulliparous women. Among these women, 43% delivered at 39 weeks’ gestation, 41% at 40 weeks, and 15% at 41 weeks. The overall rate of composite neonatal morbidity was 8.8 per 1,000 live births; compared with those who delivered at 39 weeks, composite neonatal morbidity was significantly higher for those delivered at 40 (adjusted RR [aRR], 1.22; 95% CI, 1.19–1.25) and 41 weeks (aRR, 1.53; 95% CI, 1.49–1.58).
The secondary outcome, the overall rate of composite maternal morbidity, was 2.8 per 1,000 live births. As with composite neonatal morbidity, the risk of composite maternal morbidity was also significantly higher for those delivered at 40 (aRR, 1.19; 95% CI, 1.14–1.25) and 41 weeks’ gestation (aRR, 1.56; 95% CI, 1.47–1.65) than at 39 weeks.
Thus, among low-risk nulliparous pregnancies, there is an incremental increase in the rates of composite neonatal and maternal morbidity from 39 to 41 weeks.
Is induction of labor at 39 weeks feasible?
As the evidence demonstrating multiple benefits of 39-week inductions increases, concerns regarding the feasibility and cost of implementation in the current US health care system mount. A planned secondary analysis of the ARRIVE trial evaluated medical resource utilization among low-risk nulliparous women randomly assigned to elective induction at 39 weeks or expectant management.6 Resource utilization was compared between the 2 groups during the antepartum period, delivery admission, and from discharge to 8 weeks postpartum.
For the antepartum period, women in the induction group were significantly less likely than women undergoing expectant management to have at least 1: office visit for routine prenatal care (32.4% vs 68.4%), unanticipated office visit (0.5% vs 2.6%), urgent care/emergency department/triage visit (16.2% vs 44.3%), or hospital admission (0.8% vs 2.2%). When admitted for delivery, as expected, women in the induction group spent significantly more time on the L&D unit (14 hours vs 20 hours) and were more likely to receive interventions for induction (cervical ripening, oxytocin, intrauterine pressure catheter placement). However, they required magnesium sulfate and antibiotics significantly less frequently. For the postpartum group comparison, women in the induction group and their neonates had a significantly shorter duration of hospital stay.
In summary, the investigators found that, compared to women undergoing expectant management, women undergoing elective induction spent longer duration in L&D units and utilized more resources, but they required significantly fewer antepartum clinic and hospital visits, treatments for hypertensive disorders or chorioamnionitis, and had shorter duration of postpartum length of stay.
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