Prenatal Diagnosis of Thalassemia

Thalassemia is an individual as well as a community health problem in some countries. It causes a lifelong suffering for the affected individuals. There is no treatment other than supportive, i.e. regular transfusions and removal of iron overload from the body. Only by such continuous and expensive treatment thalassemic patients can-generally achieve nearly normal health, but the health burden of such therapy for a large number of thalassemic patients is unaffordable by the affected communities. Prevention of the births of thalassemic babies is the choice for controlling the thalassemia and has been successful in many countries. For this purpose reliable and time accurate prenatal diagnosis is a conditio sine qua non. Blood fetal sampling is safe and can be done after 16 weeks gestation, amniocentesis after 14 weeks, and even chorionic villi sampling as early as 8 weeks gestation. In vitro globin synthesis analysis applied to the fetal blood sample is very reliable to measure the rate of synthesis of the globin chains that make up the hemoglobin. The-DNA analysis of the fibroblasts obtained by amniocentesis or of the chorionic villus sample is very sensitive and specific for the diagnosis of the genetic disorder in thalassemias. By involving the prenatal diagnosis, the birth of B-homozygous thalassemia has decreased by up to 90%.

Hematocrit of the fetal rabbit placenta

51Cr-labeled erythrocytes and [125I]RISA were used simultaneously to measure the fetal rabbit whole-body and placental hematocrits (Hct) and to find the ratio of placental transit times of erythrocytes and plasma. The levels were injected into the heart of 21 fetal rabbits of 26--28 days gestation, and about 60 s mixing time, the placenta and a fetal blood sample were assayed with a gamma well-type scintillation counter. Erythrocyte and plasma activity per milliliter were determined from a standard dilution of the isotopes. Large-vessel Hct was measured as the corrected packed erythrocyte percentage in capillary tubes. Large-vessel Hct was 37.3 (+/- 3.7 SD) %, whole-body Hct was 31.3 (+/- 3.5) %, and the placental Hct was 25.3 (+/- 4.0) %. The placental/large-vessel Hct ratio was 0.676. The ratio may be estimated as 0.765 when corrected for the loss of albumin in time. The transit time of erythrocytes in the placenta was calculated to be 0.682 of that for plasma. The shorter erythrocyte transit time implies that there is less time for O2 and CO2 exchange than previously thought.