Invasive Tests and Procedures

Invasive prenatal tests are performed for a variety of reasons, the most common indication being genetic diagnosis. Benefits:

• Provide reassurance to the couple, when normal
• Enable safer, earlier termination of pregnancy if the results are abnormal, and
• For patients, who do not desire termination, allow for planning a management strategy for the remainder of the pregnancy and also post-delivery

Chorion villous sampling (CVS)

CVS is performed between 11 – 14 weeks. It involves passing a very fine needle through the mother’s abdomen (local anaesthesia is given) and obtaining a sample of villi from the placenta. The placenta is essentially a fetal organ and hence is tested as a proxy to the fetus.

The procedure is done under continuous USG guidance to avoid harm to the fetus. CVS is generally safe and the risk of miscarriage is < 1%.

Amniocentesis

Amniocentesis involves inserting a very fine needle under USG guidance through the maternal abdomen to obtain a sample of the fluid surrounding the fetus. Fetal cells in the fluid are then harvested, cultured and tested.

It is usually performed between 15 – 20 weeks and the risk of pregnancy loss is the same as CVS.

Fetal Blood sampling (FBS)

In addition to genetic disorders and infections, FBS enables diagnosing certain blood conditions (e.g., anemia) in the fetus and is generally performed after 18 weeks. It involves obtaining a sample of the fetal blood from the umbilical cord. 

FBS carries a higher risk of complications and hence is less commonly performed compared to CVS or Amniocentesis.

Intra-uterine blood transfusion (IUT)

IUT is a procedure that is performed in case of severe fetal anemia. The most common cause of fetal anemia in India is Rh alloimmunization. The rationale in doing IUT is to replace the fetal blood cells that are being destroyed by the Rh sensitized maternal immune system and thereby keep the fetus healthy till delivery.

Transfusions are given into the cord, a blood vessel in the fetal liver or rarely into the fetal abdomen. The procedure is done with careful USG monitoring to avoid injury to the fetus.

Fetal Reduction (FR)

In higher order multifetal pregnancies (>2 fetuses), non-directive counseling is offered explaining risks unique to such pregnancies (preterm birth with its attendant complications) and the option of FR given. 

Fetal reduction is performed in the first trimester or early second trimester to reduce the number of fetuses to twins and thereby improve the pregnancy outcome.