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Effect of delivery mode on neonatal mortality in very low birth weight(VLBW) births has been controversial. We examined this question, using the U.S. Linked Birth/Infant Death Data Sets for three years, 1989-91. Of all VLBW live births (n=141,497), 47.9% were delivered by primary vaginal delivery, 1.5% by vaginal delivery with a history of previous C-section, 37.5% by primary C-section, 7.0% by repeat C-section, and 6.2% by unknown mode of delivery. Only the VLBW (<1,500 gms) live births delivered by primary vaginal delivery or by primary C-section were examined. Neonatal mortality rates (NMR) were expressed by age of death per 1,000 live births for <1hr and <28 days NMR and per 1,000 survivors for 1-23 hrs, 1-6 days, and 7-27 days NMR. In all VLBW groups, births by primary C-section was associated with a significantly lower <1hr NMR, compared to the births by primary vaginal delivery (Table). This difference in <1hr NMR was progressively greater with a decrease in birth weight. The association of low NMR with C-section persisted throughout the entire neonatal period in the 500-749 gm group, but only up to 23 hrs of life in the remaining VLBW groups. Primary C-section was associated with low overall (<28 days) NMR only in the <1,000 gm births and not in the 1,000-1,499 gm group, however.
Table 1 Table. Age- and birth weight-specific NMR by mode of delivery, the U.S., 1989-91
