Time of Delivery Among Low-Risk Women at 37-42 Weeks of Gestation and Risks of Stillbirth and Infant Mortality, and Long-term Neurological Morbidity

Time of delivery in low-risk pregnancies is an important consideration for clinicians. They must balance the risks associated with early delivery, including respiratory and other neonatal complications, versus those associated with later delivery, including stillbirth, meconium aspiration syndrome and maternal complications. Moreover, delivery post maturity has been associated with neurodevelopmental disorders, such as cerebral palsy (CP) and epilepsy. The aim of this study was to assess the impact of time of delivery on the risks of stillbirth, infant mortality, CP, and epilepsy in low-risk pregnancies. This was a population-based study using data from Swedish national population and health registries between January 1, 1998, and December 31, 2019. Included were low-risk, singleton pregnancies with live births and stillbirths at >= 37 weeks of gestation. Excluded were infants delivered at >= 43 weeks, those in breech presentation, and those whose mothers had chronic diseases or certain pregnancy complications. Delivery at a given gestational week was compared with delivery at later gestational weeks to assess the outcomes of stillbirth, infant mortality, CP, and epilepsy. A total of 1,773,269 infants were included in the study, including 2736 cases of stillbirth, 1981 cases of infant death, 2649 cases of CP, and 12,877 cases of epilepsy. Overall, the rates of stillbirth and infant mortality decreased from 37 to 40 weeks of gestation and then increased at 41 and 42 weeks. The risks of stillbirth were higher at 37 versus >= 38 weeks (adjusted relative risk [aRR], 3.88; 95% confidence interval [CI], 3.47-4.34) and at 38 versus >= 39 weeks (aRR, 1.96; 95% CI, 1.76-2.17). The risks of infant mortality were higher at 37 versus >= 38 weeks (aRR, 2.45; 95% CI, 2.10-2.86) and at 38 versus >= 39 weeks (aRR, 1.61; 95% CI, 1.42-1.82). In addition, the adjusted risks for infant mortality decreased by 20% among live births at 40 versus >= 41 weeks of gestation and 25% among live at 41 versus 42 weeks of gestation. Overall, the rate of CP was lowest at 40 weeks and highest at 37 and 42 weeks. The risk of CP was higher at 37 versus >= 38 weeks (aRR, 1.60; 95% CI, 1.37-1.87) and at 38 versus >= 39 weeks (aRR, 1.19; 95% CI, 1.06-1.33). Overall, the rate of epilepsy declined from 37 to 40 weeks and then slightly increased at 42 weeks of gestation. The risk of epilepsy was also higher at 37 versus >= 38 weeks (aRR, 1.24; 95% CI, 1.15-1.34) and at 38 versus >= 39 weeks (aRR, 1.12; 95% CI, 1.07-1.18). In conclusion, between 39 and 40 weeks of gestation is the optimal time of delivery in low-risk pregnancies to reduce the risk of stillbirth, infant mortality, and adverse neurodevelopmental outcomes.

Automated summary

The optimal time of delivery in low-risk pregnancies to reduce the risk of stillbirth, infant mortality, and adverse neurodevelopmental outcomes is between 39 and 40 weeks of gestation.