Genetic amniocentesis: 505 cases performed before the sixteenth week of gestation.

Between May 1987 and November 1988, 505 early amniocentesis within the 15th week of gestation were performed at the First Department of Obstetrics and Gynaecology, 'L. Mangiagalli' of the University of Milan and at the Department of Obstetrics and Gynaecology of 'Gaslini' hospital in Genoa. A total number of ten abnormal fetal karyotypes were diagnosed.