Genetic amniocentesis in twin pregnancies: results of a multicenter study of 529 cases.

To evaluate the risk of abortion after genetic amniocentesis in twin pregnancies, a retrospective study of 15 centers was performed. The spontaneous abortion rate up to 20 completed weeks of gestation was 2.3%; the abortion rate up to 28 completed weeks, as defined by WHO, was 3.7%. The abortion rate could not be correlated either with the number of needle insertions or with the type of marker dye used. There was also no correlation between the abortion rate and the gestational age at which amniocentesis was performed. A significant association was shown between congenital intestinal obstructions and the application of methylene blue intra-amniotically as a marker dye. Considering the increased natural loss rate in multiple gestations, amniocentesis in twin pregnancies seems to be a safe and reliable technique.