Prenatal diagnosis of heterozygous beta-thalassemia.

The parents of a child with homozygous thalassemia of the beta O variety requested prenatal diagnosis during a subsequent pregnancy. At the 19th week of pregnancy, a sample of blood containing fetal cells was obtained by placentocentesis. Radiochromatography of globin chains demonstrated production of a beta-chain with a beta/gamma synthetic ratio of 0.049, which is low for this gestational age. The conclusion that the child would be heterozygous for the beta-thalassemia gene was confirmed after birth.