Think Foundation
Knowledge Centre - Pre Natal Diagnosis

In the event of both partners in a marriage being Thalassaemia Minor, genetic counseling should be provided by a trained counselor. Information should be made available to the couple at risk so as to enable them to make an informed choice. It should be made clear to them that they carry the risk of producing a Thalassaemia Major child. There is a one-in-four chance in every pregnancy of their child being a Thalassaemia Major.

It is possible to go for a Pre Natal Test, very early in the pregnancy, and figure out if the foetus is Thalassaemia Major. An informed decision can be taken on whether to continue with the pregnancy or not. While making a decision on the Pre Natal Diagnosis, the couple at risk needs to be informed about the procedure of diagnosis, the risk of miscarriage after the procedure and the chances of misdiagnosis. The different methods for Pre Natal Diagnosis are Chorionic Villi Sampling (CVS), Amniocentesis and Foetal Blood Sampling.

Chorionic Villi Sampling (CVS)

This can be done in the first trimester of pregnancy, and the results are reliable. The developing placenta is known to have the same genetic make-up as the foetus. CVS involves collecting a sample of the developing placenta, by means of a needle inserted through the abdominal wall. The transabdominal CVS under ultrasound guidance has been routinely performed form gestation of 6 weeks until the third trimester.

The advantages of CVS are reliable results, quicker results and early detection. This also means lesser emotional stress due to earlier decision if termination of pregnancy is required.


This is conventionally done from 16 weeks’ gestation onwards. The amniotic fluid surrounds the foetus in the amniotic cavity. In amniocentesis 15-20 ml of the amniotic fluid is withdrawn by inserting a needle into the abdomen under ultrasound guidance.

Late diagnosis is the major disadvantage of this method, particularly so when the foetus is affected and termination of pregnancy is sought.

Foetal Blood Sampling

This can be carried out after 20 weeks of pregnancy. The procedure involves inserting a needle under ultrasound guidance through the abdominal wall and collecting a sample of foetal blood from the umbilical cord.