Endocardial fibroelastosis in growth-discordant monozygotic twins

Two cases of fetal endocardial fibroelastosis are reported in the larger of growth-discordant monozygotic twins. The growth discordance in these two cases is regarded as a manifestation of twin-twin transfusion syndrome, but other causes are considered and the difficulties posed by the observed placental vascular anatomy are discussed. The literature on endocardial fibroelastosis in multiple pregnancy is briefly reviewed, and the relationship of endocardial fibroelastosis to the cardiovascular compromise seen in twin-twin transfusion syndrome is considered.