Prenatal diagnosis of haemoglobinopathies: our experience of 523 cases.

Background: We performed counselling for prenatal diagnosis (PD) of haemoglobinopathies in 372 couples. Thirty-four out of 372 (9.1%) did not undergo PD: six due to spontaneous abortion; nine because it was too difficult to make a decision if PD was positive; 18 because counselling excluded the carrier status of one or both parents; and one because parental mutations were mild.
Methods: Eleven out of 338 (3.3%) couples underwent PD because they had a thalassaemic child; 106 (31.4%) were found to be at high risk during pre-conceptional screening; 221 (65.4%) because of familiarity. Of 523 PDs in 486 (92.9%), including six dichorionic twin pregnancies, PD was performed on DNA from chorionic villi (CV), and in 37 from amniocytes (7.1%). In 1/523 cases, PD was not completed because DNA from CV was not sufficient; in two cases single tandem repeat analysis revealed maternal contamination of foetal DNA; in 7/522 (1.3%) cases PD revealed non-paternity. In 435/522 (83.3%) cases, PD was performed using reverse dot-blot and ARMS; 34/522 (6.5%) required sequencing. In 53/522 (10.2%) cases it was necessary to test globin loci for large rearrangements.
Results: One hundred and twenty out of 522 (23.0%) PDs revealed an affected foetus. In all but two cases the couple interrupted pregnancy. In the six twin pregnancies PD revealed a normal and a carrier foetus (two cases), carrier status in both foetuses (two cases) and a carrier and an affected foetus (two cases). In these latter cases the couple planned selective interruption.
Conclusions: Our PD procedure is successful and reliable, and is useful in high-risk areas characterised by molecular heterogeneity.