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Percutaneous Umbilical Blood Sampling
Percutaneous umbilical blood sampling (PUBS), also called cordocentesis, is a test done on the fetus while it is still developing inside your uterus. The advantage of the test is that results are available in a few days. The disadvantage is that it carries a slightly higher risk of miscarriage than amniocentesis does.

Guided by ultrasound, a fine needle is inserted through the mother's abdomen into a tiny vein in the umbilical cord. A small sample of the baby's blood is removed for analysis. PUBS detects blood disorders, infections and Rh-incompatability.

The baby's blood can be checked before birth, and the baby can be given a blood transfusion, if necessary. This procedure can help prevent life-threatening anemia that may develop if the mother is Rh-negative and has antibodies that are destroying her baby's blood.