Fetal Diagnosis

Sickle cell can be identified while the mother is still pregnant. This is called, fetal diagnosis. Fetal diagnosis is possible for about 90% of pregnancies. But it is stressed that a previous homozygous normal or affected child or, otherwise, the couple's parents are necessary to confirm the linkage of variant genes to respective DNA markers. And if the appropriate markers are identified and their linkage to the sickle cell genes is verified, then the diagnosis can be performed at 16-18 weeks.

At first, fetal diagnosis was performed on a small amount of fetal blood from the placenta, umbilical cord, or fetal heart, either blindly, with ultrasound guidance, or through a fetoscope at the 20th week of pregnancy. But this fetal blood procedure was associated with 1-2% fetal loss and during the mid-trimester diagnosis of the affected fetus frequently led to a painful abortion. But the introduction of DNA techniques have took this procedure’s place. These techniques permit precise fetal diagnosis in the first trimester and termination of pregnancy.

The use of amniotic cells is the easiest way to DNA analysis. It provides results after the 17th week of pregnancy. The technique uses the aspiration of amniotic fluid with a long needle which is painless and safe. About 20 ml of fluid contains enough amniotic cells for removal of up to 20ug of DNA to identify the defect. The risk of fetal loss is lower than 0.5%.