Genetic amniocentesis in twin pregnancies.

Eighty-three patients with twin pregnancies were seen at the University Hospital of Rotterdam between 1 January 1980 and 31 August 1985 for prenatal genetic studies. No abnormal karyotypes were found. Amniotic fluid was successfully obtained from both amniotic sacs in 77 patients. In two pregnancies elevated levels of alpha-fetoprotein (AFP) were found in both sacs. One of these pregnancies was terminated and the other continued until term. One pregnancy miscarried 4 weeks after amniocentesis at 19 weeks gestation; three women were delivered between 23 and 28 weeks, 36 at between 28 and 37 weeks and 42 women after 37 weeks. The perinatal mortality rate was 55/1000 (9 of 164). These results show that genetic amniocentesis is a safe and reliable technique in twin pregnancy but the interpretation of elevated AFP levels is complicated by the fact that AFP diffuses across the amniotic membranes between the two sacs.