Twin gestation: influence of placentation on fetal growth.

To study fetal growth in twin gestation, morphometric autopsy data of 52 midgestation twin pairs who were stillborn or who died less than or equal to 24 hours after birth were analyzed. Twins were divided into three groups: (1) monozygotic: diamniotic, monochorionic placenta (n = 18); (2) dizygotic: diamniotic, dichorionic placenta, unlike sex (n = 12); (3) like-sex: placenta diamniotic, dichorionic in 63.6%, unknown in 36.4% (n = 22). The monozygotic group had a significantly higher rate of growth discordance, which was defined as a greater than 20% difference in body weight (monozygotic 72.2%, dizygotic 16.7%, like-sex 0%), and polyhydramnios (monozygotic 50%, dizygotic 0%, like-sex 9.1%). Organ weight z scores for body weight and brain weight standards were calculated for the smaller and larger of each twin pair. In the monozygotic group highly significant z scores were obtained for brain weight in the smaller twin (z = 2.71, p = 0.003, body weight standards) and heart weight in the larger twin (body weight standards, z = 3.87, p less than 0.001; brain weight standards, z = 3.64, p less than 0.001). We conclude that monozygotic twins with diamniotic, monochorionic placentation have a high degree of brain-sparing growth restriction in the smaller twin and cardiac hyperplasia in the larger twin, most likely caused by hemodynamic inequalities.