Maternal and Perinatal Outcomes of Expectant Management of Full-Term, Low-Risk, Nulliparous Patients.

OBJECTIVE To compare risks of maternal and perinatal outcomes by completed week of gestation from 39 weeks in low-risk nulliparous patients undergoing expectant management. METHODS We conducted a secondary analysis of a multicenter randomized trial of elective induction of labor at 39 weeks of gestation compared with expectant management in low-risk nulliparous patients. Participants with nonanomalous neonates, who were randomized to and underwent expectant management and attained 39 0/7 weeks of gestation, were included. Delivery gestation was categorized by completed week: 39 0/7-39 6/7 (39 weeks), 40 0/7-40 6/7 (40 weeks), and 41 0/7-42 2/7 (41-42 weeks) (none delivered after 42 2/7). The coprimary outcomes were cesarean delivery and a perinatal composite (death, respiratory support, 5-minute Apgar score 3 or less, hypoxic ischemic encephalopathy, seizure, sepsis, meconium aspiration syndrome, birth trauma, intracranial or subgaleal hemorrhage, or hypotension requiring vasopressor support). Other outcomes included a maternal composite (blood transfusion, surgical intervention for postpartum hemorrhage, or intensive care unit admission), hypertensive disorders of pregnancy, peripartum infection, and neonatal intermediate or intensive care unit admission. For multivariable analysis, P<.0125 was considered to indicate statistical significance for the coprimary outcomes. RESULTS Of 2,502 participants who underwent expectant management, 964 (38.5%) delivered at 39 weeks of gestation, 1,111 (44.4%) at 40 weeks, and 427 (17.1%) at 41-42 weeks. The prevalence of medically indicated delivery was 37.9% overall and increased from 23.8% at 39 weeks of gestation to 80.3% at 41-42 weeks. The frequency of cesarean delivery (17.3%, 22.0%, 37.5%; P<.001) and the perinatal composite (5.1%, 5.9%, 8.2%; P=.03) increased with 39, 40, and 41-42 weeks of gestation, respectively, and hypertensive disorders of pregnancy decreased (16.4%, 12.1%, 10.8%, P=.001). The adjusted relative risk, 95% CI (39 weeks as referent) was significant for cesarean delivery at 41-42 weeks of gestation (1.93, 1.61-2.32) and for hypertensive disorders of pregnancy at 40 weeks (0.71, 0.58-0.88) and 41-42 weeks (0.61, 0.45-0.82). None of the other outcomes were significant. CONCLUSION In expectantly managed low-risk nulliparous participants, the frequency of medically indicated induction of labor, and the risks of cesarean delivery but not the perinatal composite outcome, increased significantly from 39 to 42 weeks of gestation.