Third trimester perinatal mortality associated with immediate delivery versus expectant management according to birthweight category.

Objective: Immediate delivery compared with expectant management in a low risk population stratified by birthweight.

Methods: Retrospective cohort of births, stillbirths and neonatal deaths from 2010 through 2012 compiled by the National Center for Health Statistics. Birthweight categories were created using population derived deciles. Gestational age at birth was adjusted to account for time from death to delivery. The risk of immediate delivery was the neonatal death rate. The risk of expectant management was the sum of the conditional stillbirth risk plus the neonatal death rate for the following week. Relative risks were calculated comparing immediate delivery with expectant management by birthweight category.

Results: There were 4 966 067 births, 6660 stillbirths and 6979 neonatal deaths. The gestational age at which expectant management exceeded risk of immediate delivery was consistently at or after 39 weeks for all except birthweights above the 95th centile, where the relative risk for death with immediate delivery was 1.72 (95% CI: 1.74-1.7) at 36 and 0.83 (95% CI: 0.84-0.81) by 37 weeks.

Conclusions: In this low risk cohort, risk at 39 weeks favored immediate delivery, except for birthweight over the 95th centile, where expectant management did not appear to be beneficial after 37 weeks.