Genetic amniocentesis in multiple pregnancy.

Eleven cases of twin pregnancy presenting for genetic diagnosis in the second trimester are reported. In all 11 cases, a correct chromosomal diagnosis was made on each of the twins. The technique used required only ultrasound and Evan's blue dye for direction of the amniocentesis. Amniography was not performed. The technique used is described in detail, and its advantages over more standard techniques are described.