The risk of intrapartum/neonatal mortality and morbidity following birth at 37 weeks of gestation: a nationwide cohort study.

objectiveTo assess intrapartum/neonatal mortality and morbidity risk in infants born at 37 weeks of gestation compared with infants born at 39-41 weeks of gestation.

designNationwide cohort study.

settingThe Netherlands. POPULATION: A total of 755 198 women delivering at term of a singleton without congenital malformations during 2010-14.

methodsWe used data from the national perinatal registry (PERINED). Analysis was performed with logistic regression and stratification for the way labour started and type of care.

main outcome measuresIntrapartum or neonatal mortality up to 28 days and adverse neonatal outcome (neonatal mortality, 5-minute Apgar <7, and/or neonatal intensive care unit admission).

resultsAt 37 weeks of gestation intrapartum/neonatal mortality was 1.10‰ compared with 0.59‰ at 39-41 weeks (P < 0.0001). Adjusted odds ratio (aOR) for 37 weeks compared with 39-41 weeks was 1.84 (95% CI) 1.39-2.44). Adverse neonatal outcome at 37 weeks was 21.4‰ compared with 12.04‰ at 39-41 weeks (P < 0.0001) with an aOR 1.63 (95% CI 1.53-1.74). Spontaneous start of labour at 37 weeks of gestation was significantly associated with increased intrapartum/neonatal mortality with an aOR of 2.20 (95% CI 1.56-3.10), in both primary (midwifery-led) care and specialist care. Neither induction of labour nor planned caesarean section showed increased intrapartum/neonatal mortality risk.

conclusionsBirth at 37 weeks of gestation is independently associated with a higher frequency of clinically relevant adverse perinatal outcomes than birth at 39-41 weeks. In particular, spontaneous start of labour at 37 weeks of gestation doubles the risk for intrapartum/neonatal mortality. Extra fetal monitoring is warranted. TWEETABLE ABSTRACT: Birth at 37 weeks of gestation gives markedly higher intrapartum/neonatal mortality risk than at 39-41 weeks, especially with spontaneous start of labour.