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