The risk of fetal death: current concepts of best gestational age for delivery

To compare the risk of fetal death (FD) between 34 and 41 weeks' gestational age (GA) with the neonatal mortality rate to examine the best GA for delivery.

Linked birth and infant death data for the US from the National Center for Health Statistics analyzed nonanomalous singleton pregnancies between 2003 and 2005. Pregnancies were classified as high risk or low risk based on preexisting maternal complications. Outcomes of 8,785,132 live births and 12,777 FDs between 34 and 42 completed weeks' gestation were examined. The risk of FD was determined using the following equation: The FD risk of those remaining undelivered was compared with the neonatal death rate for each week of gestation.

Between 34 and 40 weeks' gestation, the FD risk of those remaining undelivered for all pregnancies declined and then increased at term. For high risk pregnancies, the FD risk of those remaining undelivered is substantially higher than for low risk pregnancies. The number of FDs that can be avoided by delivery exceeds the neonatal death rate between 37 and 38 weeks' gestation in low risk pregnancies and at 36 weeks' gestation in high risk pregnancies.

These findings suggest that delivery at 39 weeks' gestation in both high and low risk pregnancies would result in an increased number of perinatal deaths. Decisions regarding the "optimal time for delivery" should include the risk of remaining undelivered.