Fetal blood sampling is part of diagnosing, monitoring and treating fetal problems at various times during pregnancy. A fetal blood sample may be obtained to diagnose genetic or chromo-some abnormalities and to check for and treat severe fetal anemia or other haematological problems. 

It can be used in conditions such as Rh incompatibility to assess the fetal anaemia and to perform fetal blood transfusions.

It can be used to check for fetal infection or to give certain medications to the fetus.

There are several ways in which blood can be obtained from the fetus. After cleansing the mother’s abdomen with an antiseptic, a long, thin needle is inserted into the mother’s abdomen under continuous ultrasound guidance.  Blood may be taken from the various sources like blood vessels of the umbilical cord (also called cordocentesis, or percutaneous umbilical blood sampling, or PUBS) a fetal blood vessel, usually in the liver or heart.

Fetal blood transfusions are performed using a similar technique in cases of fetal anaemia.