Fetal biometry and outcome in monochorionic vs. dichorionic twin pregnancies; a retrospective cross-sectional matched-control study.

Fetal biometry, amniotic fluid volume distribution and perinatal outcome were determined in a retrospective, cross-sectional matched-control study design, including 20 monochorionic (MC) twin pregnancies and 20 dichorionic (DC) twin pregnancies (historic controls). Intertwin differences for fetal abdominal circumference were larger in the MC subset than in the DC subset. Fetofetal transfusion syndrome, based upon a combination of oligohydramnios in one sac and polyhydramnios in the other sac, existed in 40% (8 of 20) of the MC twin pregnancies, but in none of the DC twin pregnancies. Mean gestational age at delivery was significantly shorter in the MC subset (30.9 weeks) than in the DC subset (34.3 weeks). The perinatal death rate was significantly higher in MC twin pregnancies (50%) than in DC twin pregnancies (15%). No differences were established for intertwin weight estimates by ultrasound and birth weight between both subsets. The poor perinatal outcome in monochorionicity is mainly a result of the degree of premature delivery.