OBJECTIVE: This study aimed to evaluate the risks of stillbirth, neonatal mortality, and severe neonatal morbidity by comparing expectant management with delivery from 37+0 weeks of gestation.

STUDY DESIGN: This was a retrospective cohort study evaluating women with singleton, nonanomalous pregnancies at 37+0 to 40+6 weeks' gestation in Queensland, Australia, delivered from 2000 to 2018. Rates of stillbirth, neonatal death, and severe neonatal morbidity were calculated for <3rd, 3rd to <10th, 10th to <25th, 25th to <90th, and ≥90th birthweight centiles. The composite risk of mortality with expectant management for an additional week in utero was compared with rates of neonatal mortality and severe neonatal morbidity.

RESULTS: Of 948,895 singleton, term nonanomalous births, 813,077 occurred at 37+0 to 40+6 weeks' gestation. Rates of stillbirth increased with gestational age, with the highest rate observed in infants with birthweight below the third centile: 10.0 per 10,000 (95% confidence interval, 6.2-15.3) at 37+0 to 37+6 weeks, rising to 106.4 per 10,000 (95% confidence interval, 74.6-146.9) at 40+0 to 40+6 weeks' gestation. The rate of neonatal mortality was highest at 37+0 to 37+6 weeks for all birthweight centiles. The composite risk of expectant management rose sharply after 39+0 to 39+6 weeks, and was highest in infants with birthweight below the third centile (125.2/10,000; 95% confidence interval, 118.4-132.3) at 40+0 to 40+6 weeks' gestation. Balancing the risk of expectant management and delivery (neonatal mortality), the optimal timing of delivery for each birthweight centile was evaluated on the basis of relative risk differences. The rate of severe neonatal morbidity sharply decreased in the period between 37+0 to 37+6 and 38+0 to 38+6 weeks, particularly for infants with birthweight below the third centile.