Prenatal diagnosis of haemoglobinopathies: A status report.

An international registry of prenatal tests for haemoglobinopathies has been kept since July, 1974. Up to March, 1981, 1856 tests had been done with fetal blood and 70 with amniotic fibroblast DNA in 21 centres. Of the tests on fetal blood 92% were for the diagnosis of thalassaemia and 8% for that of sickle disorders. Blood was sampled via fetoscopy in 67% of cases and by placental aspiration in 33%. Adequate samples were obtained in 97% of cases. With fetoscopy the proportion of red cells obtained that were of fetal origin was 92%, and with aspiration it was 57%. In the most recent year of the registry the fetal loss rate was 3.9% (of 725 cases); and the rate was 5.6% overall (5.2% by fetoscopy and 6.5% by aspiration). Affected fetuses were detected in 23% of cases at risk for thalassaemia, and in 15% at risk for sickle disorders. The error rate was 0.9% and consisted mostly of false negatives. Fibroblast DNA analyses were used to assess the risk of sickle disorders in 61 (87%) of the 70 cases studied. 24% were affected. 26% had exclusion diagnoses only. The use of prenatal tests, together with genetic screening and counselling, has considerably reduced the rate at which new homozygous thalassaemics are born in several regions of the world.