Objective: The purpose of this study was to evaluate neonatal mortality rates among discordant twins, classified according to the birth weight of the smaller twin.
Study design: We compared neonatal mortality rates among three groups of discordant twins (>25%), distinguished by the birth weight of the smaller twin being <10th, 10th to 50th, or >50th percentile.
Results: Among the 10,683 pairs of twins who were studied, the respective proportions of the three groups were 62.4%, 32.9%, and 4.7%. The neonatal mortality rate was significantly higher among pairs in which the smaller twin weighed <10th birth weight percentile (29. vs 11.1 and 11 per 1000; odds ratio, 2.7; 95% CI, 1.3, 5.7). This difference results from the higher mortality rates among the smaller but not among the larger twins.
Conclusion: Severely discordant twin pairs in whom the smaller twin is also small for gestational age are at an increased risk of neonatal death. Identification of this group is an imperative step in the management of birth weight discordance in twin gestations.