Method of delivery and neonatal mortality among very low birth weight infants in the United States.

OBJECTIVE: To examine the association between method of delivery (primary cesarean section vs. vaginal) and neonatal mortality risk (as well as causes of death) among very low-birth weight first-born infants in the United States. More specifically, to examine this association separately for breech/malpresenting and vertex-presenting infants, while adjusting for selected maternal characteristics, and pregnancy, labor and delivery complications.
METHODS: The study population was derived from the 1995-1998 birth cohort linked birth/infant death data sets. Binary and multinomial logit regression analyses were performed to assess the relationship in four very low-birth weight categories.
RESULTS: Among breech/malpresenting neonates, compared to those delivered vaginally, infants delivered by a primary cesarean section had significantly lower adjusted relative risks of death for all very low-birth weight categories and the decrease in relative risk tended to be larger with each increasing birth weight category. However, for vertex-presenting neonates, results are mixed, suggesting decreased relative mortality risks associated with primary cesarean section, which were significant for 500-749 g, not significant for 750-999 g, and barely significant for 1,000-1,249 g. In contrast, for vertex-presenting neonates weighing 1,250-1,499 g, there was a significantly increased adjusted relative risk associated with primary cesarean section. Differences in cause-specific neonatal mortality by method of delivery and presentation status were also discussed.
CONCLUSIONS: Primary cesarean section appears to be associated with decreased neonatal mortality risks in each very low-birth weight category for breech/malpresenting infants, but results are mixed for vertex-presenting infants. Causal inferences should be avoided because this was an observational study by design.