Prenatal diagnosis in New South Wales: comparative view of the first 1000 cases of chromosomal, sex-linked, and metabolic referrals.

In 1000 cases referred for prenatal diagnosis, 28 affected fetuses were detected, and 24 therapeutic terminations of pregnancy were performed. There were five main reasons for referral. Among the 293 women referred because of advanced maternal age (40 years and above), there were 11 (3.8%) who had affected fetuses, while among the 439 aged 35 to 39 years there were 6 such women (1.4%). In the 112 mothers referred because of a history of a previous child with Down's syndrome, one fetus (0.9%) with trisomy 21 was detected. Of 27 cases in which one parent was a carrier of a balanced chromosomal rearrangement, two chromosomally abnormal fetuses (7.4%) were detected (the offspring of maternal carriers), and a further two spontaneous abortions occurred before the scheduled amniocentesis. In the 22 cases with a history of sex-linked disorder, there were 8 males. Nine women were referred with a possible inherited metabolic defect: one fetus affected with congenital adrenal hyperplasia was detected. The number of metabolic referrals was markedly less than in overseas studies. The finding of XXY, XXX and trisomies of chromosomes 13, 18, and 21 in fetuses of older mothers confirms the increased risk in such mothers for chromosome abnormalities in addition to trisomy 21. Sixty-two of the 1000 women (6.2%) had to have a repeat amniocentesis because of failure of culture. Of 900 births: one case of maternal cell contamination and one case of unconfirmed mosaicism were the only disparities between prenatal and postnatal karyotypes. The average time necessary to obtain the karyotypic result was 15 days after amniocentesis.