Fetal Blood Sampling (FBS)

Reviewed by Traci C. Johnson, MD on December 15, 2020

Fetal blood sampling helps check for birth defects. It's not a standard test. Doctors may suggest it if earlier tests -- such as CVS, amniocentesis, or ultrasounds -- had unclear results.

FBS helps rule out some birth defects. It can also show anemia and infections, such as rubella.

FBS has a risk of miscarriage and other problems. The risk is higher than with similar tests, such as amniocentesis and CVS. Talk over the pros and cons with your doctor.

Using ultrasound to see an image of your baby, the doctor will guide a thin needle through your womb and into a tiny blood vessel in your baby or in the umbilical cord. Your doctor will get a tiny sample of your baby's blood. You may feel some pressure or cramping. Then a lab will test the sample.

The procedure has different names depending on how your doctor gets the blood. When the doctor takes the blood from the umbilical cord, it's called percutaneous umbilical cord blood sampling (PUBS.)

Test results usually come back within three days. If they show that your baby has a problem, you will meet with your doctor or a counselor to discuss your options. If your baby has an infection or anemia, treatment can help. FBS is accurate at diagnosing some birth defects. However, it doesn't show how severe they are.

If you need fetal blood sampling, you would probably get it at about 17 to 18 weeks. This will depend on the reason for the testing, such as anemia or infection. It may also be done at any time and possibly several times.

Cordocentesis, percutaneous umbilical blood sampling, umbilical vein sampling, funiculocentesis, fetal intrahepatic blood sampling, fetal cardiocentesis

Amniocentesis, CVS

Show Sources


UNC Center for Maternal & Infant Health: "Percutaneous Umbilical Blood Sampling (PUBS)."

Yale School of Medicine: "Fetal Blood Sampling."

UptoDate: "Fetal Blood Sampling."

Johns Hopkins Manual of Gynecology and Obstetrics, 4th Edition. Lippincott Williams & Williams, 2010.

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