Fetal growth in multifetal gestation.

Multiple gestations present a significant increase in fetal growth abnormalities in direct relationship to the number of fetuses present. Various definitions of birth weight discordancy exist (> or = 15%-40%). When first trimester discordancy in CRL or gestational sac diameter or early second trimester discordancies of BPD, HC, AC, or femur length are detected, genetic counseling and further work-up, including chromosomal analysis, should be considered. AC and SEFW are the best sonographic predictors of second and third trimester growth discordancy of twins. Discordant Doppler velocimetry of the umbilical arteries enhances ultrasonographic diagnosis of twin discordancy. Karyotyping also should be considered on second or third trimester diagnosis of growth discordancy. Twin-twin transfusion should be considered when growth discordancy is diagnosed in monochorionic gestations. Concordant twins with appropriate-for-gestational-age growth parameters should be followed with repeated sonographic assessment of fetal growth at approximately 4-week intervals. Discordant twins should be followed by repeat sonographic assessment of fetal growth at closer intervals, most probably every 2 weeks. Surviving singleton fetuses, after spontaneous fetal death of a twin at > 16 weeks of gestation, should be followed with antepartum surveillance similar to that of discordant twins. In rare cases of extremely premature twins with discordant growth and deteriorating fetal well-being of the growth-restricted twin, conservative management should be considered in favor of the normally grown fetus.