Morbidity and mortality of very low birth weight multiples compared with singletons

Previous studies comparing the neonatal outcome of very low birth weight (VLBW) multiples and singletons have suggested a worse outcome for multiples at gestational ages on the limits of viability.

The objective of this study is to determine the neonatal mortality and morbidity of VLBW multiples compared to singletons.

This is a retrospective study including all infants registered in the Spanish network for infants under 1500 g (SEN1500), over a 12-year period (from 2002 to 2013). Mortality and major morbidities were compared between singletons and multiples.

About 32,770 infants were included: 21,123 singletons (64.5%) and 11,647 multiples (35.5%), with a mean gestational age of 29.5 weeks (22-38), and mean birth weight of 1115 g (340-1500). When adjusted by other perinatal factors, multiple pregnancy has a significantly higher risk of mortality than singleton pregnancy (odds ratio (OR) 1.15; IC 95% 1.05-1.26, p = .002), but not a higher risk of major morbidity or composite adverse outcome. In the subgroup of infants born before 26 weeks, multiples showed a higher risk of mortality (63.9% versus 51%, OR 1.7; 95% CI 1.47-1.96) and a higher risk of composite adverse outcome (88.9% versus 81.5%, OR 1.82, 95% CI 1.28-2.24).

In preterm infants born with less than 1500 g, multiple pregnancy is a prognostic factor that can slightly increase mortality. Extremely preterm infants born before 26 weeks have a greater risk of mortality and major morbidity if they come from a multiple pregnancy.