Characterization of the growth-discordant twin.

A computer-assisted analysis of perinatal variables was undertaken in order to characterize the growth-discordant twin. We studied 124 twin pairs grouped at four degrees of discordancy: over 5, 10, 15, and 20% birth weight difference, using the larger twin as 100%. Twins with birth weight discrepancy below these figures were considered concordant. Highly discordant second twins showed significantly lower birth weight, gestational age, and Apgar scores, and prolonged neonatal hospitalization, as compared with discordant first twins. Complex presentations and a higher cesarean section rate characterize discordant first and concordant twins. It is suggested that a 15% birth weight discordancy be used as the safety limit for birth weight disparity. We also recommend special attention when discordancy seems to increase, especially if the discordant is the second twin.