Impact of cesarean section on neonatal mortality rates among very preterm infants in the United States, 2000-2003.

The objective of this analysis was to compare the neonatal mortality rates for infants delivered through primary cesarean section versus vaginal delivery, taking into consideration a number of potentially risk-modifying conditions. US linked birth and infant death certificate files for 2000-2003 were used. Demographic, medical, and labor and delivery complications were abstracted from the files with infant information. The primary outcome examined was neonatal death (death at 0-27 days of age). Because of concern regarding misclassification of gestational age, a procedure was used to trim away births for which the birth weight for a specific gestational age was incongruous. Adjusted odds ratios were calculated for the risk of neonatal death relative to the mode of delivery (primary cesarean section versus vaginal delivery), using logistic regression analysis. There were data for 13,733 neonatal deaths and 106,809 survivors available from the trimmed data set for analysis for the 4-year period. More than 80% of pregnancies with delivery between 22 and 31 weeks of gestation experienced >or=1 risk factor. Adjusted odds ratios demonstrated significantly reduced risk of neonatal death for infants delivered through cesarean section at 22 to 25 weeks of gestation (adjusted odds ratios of 0.58, 0.52, 0.72, and 0.81 for 22, 23, 24, and 25 weeks, respectively). Cesarean section does seem to provide survival advantages for the most immature infants delivered at 22 to 25 weeks of gestation, independent of maternal risk factors for cesarean section.