Fetal blood sampling is a procedure to remove a small amount of blood 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 for oxygenation. Fetal blood sampling is usually done by a specially trained 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
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 (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. The fetus either receives blood or has unhealthy blood exchanged for healthy blood to treat some problems. In this case, 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.
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 18 weeks or later.