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Fetal Blood Sampling

Fetal blood sampling is a procedure in which a small amount of blood is removed from the fetus during pregnancy. In the past, fetal blood sampling was used only during labor through the mother's open cervix to test blood from the fetal scalp to find out how well the baby was oxygenating its blood.

Fetal blood sampling is usually done by a perinatologist (a doctor who specializes in the care of the fetus in high risk pregnancies). It is done as part of diagnosing, treating and monitoring fetal problems at various times during pregnancy. A fetal blood sample may be taken to:

  • diagnose genetic or chromosome abnormalities
  • check for and treat severe fetal anemia or other blood problems, such as Rh disease
  • check fetal oxygen levels
  • check for fetal infection
  • give certain medications to the fetus

How is fetal blood sampling performed?

There are several ways blood can be obtained from the fetus. After cleansing the mother's abdomen with antiseptic, a long, thin needle is inserted into the mother's uterus guided by ultrasound. Blood may be taken from the following sources:

  • blood vessels of the umbilical cord; this type of sampling is also called cordocentesis or percutaneous umbilical blood sampling (PUBS)
  • a fetal blood vessel, usually in the liver or heart

Fetal blood transfusions are performed using a similar technique. The fetus either receives blood or has unhealthy blood exchanged for healthy blood to treat some problems. During fetal blood transfusions, it may be necessary to give a sedative medication to keep the baby from moving.

After a fetal blood sampling procedure, mothers will need to rest in the hospital and have the fetal heart rate monitored for a few hours.

What are the risks and benefits of fetal blood sampling?

Fetal blood sampling is a very complex procedure that must be done by a specially trained doctor. It is used when other tests or procedures are not possible or not effective. It can be performed for pregnancies that are at least 18 weeks along.