Fetal Blood Sampling (FBS) With Twins

Who Gets the Test?

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.

What the Test Does

FBS helps rule out some birth defects, such as Down syndrome. 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.

How the Test Is Done

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

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

What to Know About Test Results

Test results usually come back within three days. If they show that one (or both) of your babies has a problem, you will meet with your doctor or a counselor to discuss your options. If either of your babies 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.

How Often the Test Is Done During Pregnancy

If you need fetal blood sampling, you would probably get it at about 17 to 18 weeks. This timing varies depending on the reason for the testing such as anemia or infection. It could also be done at any time during your pregnancy and possibly several times.

Other Names for This Test

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

Tests Similar to This One

Amniocentesis, CVS

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on June 25, 2018



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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