Why is fetal blood sampling done?

Fetal blood sampling, or PUBS, is done at about 18 to 19 weeks of pregnancy to evaluate for several different fetal conditions. The test is typically used when less invasive tests or procedures, such as chorionic villus sampling (CVS) or amniocentesis, are unavailable or have not provided conclusive results.

PUBS is often used to diagnose blood disorders, like fetal anemia, but it can also diagnose fetal infections, such as toxoplasmosis, and certain genetic conditions. During the test, your doctor can perform a blood transfusion or deliver medications to your baby without inserting another needle.

Within the Fetal Center at Riley Children’s Health, the highly skilled maternal-fetal medicine physicians specializing in fetal intervention perform this delicate procedure. Our specialists have extensive training and experience and partner with a multidisciplinary team to offer compassionate and expert care. Riley Children’s has performed PUBS for over a decade.

Are there any risks with fetal blood sampling?

Since fetal blood sampling is an invasive procedure, it does come with some risks. These risks include:

Bleeding
Infection to the mother, baby, or both
Preterm labor
Preterm birth
Premature rupture of membranes (PROM)

While there are risks, some benefits of fetal blood sampling include:

Knowing specific information about your baby’s health
The ability to treat a fetus during pregnancy with certain conditions like fetal anemia

If the doctor thinks your baby might be anemic (low blood count) or low platelet count, this test is the only way to know because it tests the baby’s blood rather than amniotic fluid. If the baby needs a blood transfusion or fluids during the same test, the doctor can give those while the same needle is still in the umbilical cord.

Your doctor may recommend this test if:

An abnormality was found on a prenatal ultrasound
Results from other tests are not certain
Rh incompatibility is an issue
Your baby might have an infection (such as toxoplasmosis)

What to Expect

Preparing for your procedure

Before your scheduled procedure, you will be instructed not to eat or drink anything after midnight the evening before your appointment. When you arrive at the Riley Maternity Tower, your healthcare team will get you checked in. They may give steroid injections as a precaution to help develop your baby’s lungs if an emergency C-section is needed. You will also receive antibiotics to help lower the chance of an infection.

With the risk of needing an emergency C-section, our team takes extra steps to prepare. Your fetal blood sampling procedure will occur near an operating room, with team members from labor and delivery, anesthesiology and neonatology made aware of the procedure. If you need an emergency delivery, be assured that your healthcare team is ready.

What happens after fetal blood sampling?

After your procedure, you’ll need to rest in the hospital while your baby’s heart rate and other vitals are monitored over a few hours. Typically, you can leave later in the day after the procedure is performed, but you will need to have someone drive you home.

The results typically take several days to come back. You will have a follow-up appointment with Riley Maternal-Fetal Medicine or Fetal Center within a week of the procedure.

Key Points to Remember

Fetal blood sampling, or PUBS, is a diagnostic test during pregnancy that’s used when other more common tests like CVS or amniocentesis are not an option or have given inconclusive results
While there are risks, the benefits can include getting more detailed information about your baby’s health and the ability to treat severe blood disorders before birth
The Riley Maternity Tower provides access to all necessary specialties for both mom and baby to ensure coordination of care in the unlikely event a complication occurs