Prenatal diagnosis in 3,000 women for chromosome, X-linked, and metabolic disorders.

In 3,000 women referred for prenatal diagnosis, 110(3.7%) abnormal fetuses were detected and 85 therapeutic terminations were performed. These were five main reasons for referral. Among the 2,227 women referred because of maternal age 35 years and older, there were 51 (2.3%) who had aneuploid fetuses. In the 297 women referred because of a previous child with Down syndrome, 3 aneuploid fetuses (1.0%) were detected. Of the 55 couples where one spouse was a carrier of a balanced chromosome rearrangement, 6 chromosomally abnormal fetuses were found (10.9%) (all the offspring of maternal carriers). In the latter group, five of the six heterozygotes with abnormal findings were carriers of tdic (13;21) translocations. In the 82 cases with a history of X-linked disorders, there were 40 males (49%). Thirty-five women were referred because of inborn errors of metabolism: 10 affected fetuses were found (28%). There was a greater proportion of sex-chromosome aneuploids as compared to trisomy 21 fetuses in the 35 to 39 year maternal age group. This was reversed in the group of women 40 years old and older. Of the 25 abnormal fetuses not terminated, 6 were sex chromosome aneuploids and 10 involved X-linked conditions where the progeny could be further prenatally monitored (eg, X-linked hydrocephalus) or treated (eg, hemophilia). In the remaining 9 the parents expressed divers reasons for their choice. Repeat amniocentesis was required in 2.9% of cases. One case of maternal cell contamination and one case of unconfirmed mosaicism were the only diagnostic errors found in the study. In the last 1,000 specimens referred, the average time necessary for a karyotypic result was 15.6 +/- 5.6 days after amniocentesis.