Exam Overview

Fetal blood sampling (FBS) is the collecting of fetal blood directly from the umbilical cord or fetus. The fetal blood is tested for signs of anemia and other blood problems. FBS is also known as cordocentesis or percutaneous umbilical cord blood sampling.

FBS is usually used when a Doppler ultrasound and/or a series of amniocentesis tests have first shown moderate to severe anemia.

If you are Rh-sensitized and you are carrying an Rh-positive fetus, your immune system can attack the fetus’s red blood cells. FBS is used to look at a fetus’s red blood cell count and oxygen level, and it also looks for signs that your immune system is destroying fetal red blood cells.

What happens

FBS is performed in a hospital’s outpatient surgery department. You will probably be given a sedative to reduce your and the fetus’s movement during the FBS procedure.

• The fetus may be given an injection of medicine that temporarily stops movement.
• A small area of your abdomen is numbed with an injection of local anesthetic.
• Ultrasound is used to guide a needle through your abdomen into an umbilical vein in the umbilical cord.
• A small amount of blood is withdrawn into the needle and collected.

You may be given more medicine during FBS, such as antibiotics to prevent infection or medicine to prevent preterm labor (tocolytic drugs).