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

OBJECTIVE

To 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.

DESIGN

Nationwide cohort study.

SETTING

The Netherlands.

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

METHODS

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

RESULTS

At 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.

CONCLUSIONS

Birth 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.