The influence of mode of delivery on twin neonatal mortality in the US: Variance by birth weight discordance

The purpose of this study was to examine if neonatal mortality rates (NMR) based on birth weight discordance (BWD) differ based on mode of delivery. The population-based US "matched multiple birth" database (1995 to 1998) was used to examine the effect of vaginal/vaginal (VV) and cesarean/cesarean (CC) modes of delivery (MOD) on neonatal mortality (<28 days after birth). Births at <32 weeks, congenital malformations, chromosomal anomalies, and discordant MOD (vaginal/cesarean) were excluded. The association between MOD (with CC as the reference) and neonatal mortality was expressed as relative risks (RR) with 95% CI, derived from logistic regression models. The NMR increased with increasing degrees of BWD regardless of mode of delivery. CC was associated with decreased NMR when BWD was between 20% and 40%, but this reached significance at BWD ≥40%; VV pairs had a 1.6-fold (95% CI 1.1-2.2) increased NMR compared with CC. In twins with BWD <40%, MOD has no effect on NMR. Beyond or equal to 40% discordance, there was lower NMR with cesarean-cesarean delivery.