Detection by ultrasound of abnormality in twin pregnancies during the second trimester.

Five cases of abnormality in twin pregnancies, detected by ultrasound examination during the second trimester, are reported. In four pregnancies there was a fetal malformation: discordant anencephaly, a monozygotic, heterokaryotypic twin pregnancy with coexistant Turner's syndrome and intrauterine death, concordant body stalk syndrome, and a dicephalus monster. In the other pregnancy one fetus dies in utero to become a fetus papyraceous. Four of the pregnancies were associated with raised levels of maternal serum alpha-fetoprotein, by singleton standards. Ultrasound examination proved of value in each case. Three pregnancies were terminated.