Traditionally, sonographic studies pertaining to fetal growth in multiple gestations have addressed third trimester growth of twins. Recently, data has been published about early twin discordancy, occurring in the first and second trimesters; fetal growth after fetal reduction of high-order multifetal gestations; and growth of triplets. This article will present this more recent data in depth and briefly address established data about third trimester growth of twins.
Growth discordancy in twins refers to the difference in sonographic estimated fetal weight (EFW), expressed as a percentage relation to the larger twin. Various definitions of growth discordancy exist (ranging between > 15% and 40%). Although growth discordancy is not a precise indicator of suboptimal outcome, the more severe the discordancy between twins, the more likely one is to encounter fetal compromise, growth restriction, and increased perinatal morbidity and mortality. Further, it appears that the incidence of fetal growth restriction is related directly to the number of fetuses in a multiple gestation.