What Is the PUBS Test?

Percutaneous umbilical cord blood sampling, or PUBS, is a test used to diagnose fetal abnormalities before a baby is born. This test is different from an amniocentesis and can help identify multiple concerns in the developing fetus. It is less common than amniocentesis and chorionic villus sampling (CVS) but it is still used in some cases where these tests and procedures cannot provide the information or benefit that PUBS can.

Purpose

The PUBS test is also referred to as cordocentesis. It is used to test for and diagnose a number of fetal problems during pregnancy. Although it cannot test for neural tube defects, it is often used to diagnose:

• Genetic or chromosomal abnormalities
• Fetal anemia and other blood disorders (Rh disorders, thrombocytopenia)
• Fetal oxygen levels
• Fetal infections (toxoplasmosis, nonimmune hydrops)

PUBS is also used to administer medications to the fetus and perform blood transfusions. Depending on the concern, PUBS may be used to help treat a disease or disorder of the fetus before the baby is born.

One new promising application of PUBS is a stem-cell transfusion. This has been used to successfully treat patients with conditions such as severe combined immunodeficiency (SCID) and beta thalassemia.

Risks and Contraindications

Like any procedure, PUBS is not without risks. In most cases, the benefits of performing this test outweigh the risks, but talk to your healthcare provider if you have concerns.

PUBS is typically performed around 18 weeks of pregnancy, or gestation, but can be performed later in the pregnancy if necessary.

The most common risks and complications include the following:

Bleeding

The procedure can lead to bleeding at the site of the needle insertion into the umbilical cord, in up to 30% of cases. A blood transfusion may be ordered if there is significant fetal blood loss.

A cord hematoma—a collection of blood in the umbilical cord—can occur in some cases. Most of the time, this is not a concern and can be monitored. If it causes the fetal heart rate to slow and it does not recover, an emergency c-section may be necessary.

Fetal-maternal bleeding can also occur. This is when fetal blood enters the pregnant person's circulatory system. It is typically a small amount and does not cause any problems.

Infection

Rarely, the procedure itself may cause an infection in the parent or the fetus. The risk of this happening is low if your healthcare provider uses proper cleaning and sterilization techniques before, during, and after the procedure.

Slowing of Baby's Heart Rate

It's typically temporary for the fetal heart rate to slow and generally resolves within five minutes. Your healthcare provider will monitor you and the fetus after the procedure to make sure you're recovering well.

Pregnancy Loss

As with other invasive forms of prenatal testing, there is a risk of pregnancy loss during this procedure. The rate of pregnancy loss for the PUBS procedure is about 1.3% and 1.9%. However, many people have this test when they know there is a serious problem, so it is difficult to determine if the rate is this high due to the procedure itself or if the pregnancy loss would have occurred anyway due to a disease or disorder.

Before the Test

You should have an extensive conversation with your healthcare provider prior to the procedure so that you understand the risks and benefits. They will also share details about the test to help reduce any anxiety you have.

Timing

The actual PUBS procedure does not take long—typically only a few minutes. You may expect to spend a few hours at the office or hospital for paperwork, preparation, and recovery.

Location

Sometimes the test will be performed in the healthcare provider's office or an outpatient facility. Other times it is done in a hospital setting so the pregnant person can be monitored after the procedure.

What to Wear

Wear comfortable clothes to your appointment. Your healthcare provider will likely have you change into a hospital gown for easier access to the abdomen.

Food and Drink

Your practitioner may tell you not to eat or drink after midnight the night before the procedure in case emergency surgery is necessary.

Cost and Health Insurance

This procedure is typically covered by most insurance plans since it is usually only performed when medically necessary. Your out-of-pocket cost will depend on your insurance coverage, deductible, etc.

What to Bring

Although the test is often performed in a medical office and generally only takes a few minutes, it may be best to bring an extra set of clothes and supplies to stay in the hospital overnight.

Because this test is typically only performed when the healthcare provider is concerned about a problem with fetal development, there may be a need for further intervention, testing, or surgery that was not originally anticipated. You should bring a spouse, partner, or another trusted friend to the appointment with you for emotional and physical support if needed.

During the Test

Pre-Test

You may be given an IV antibiotic 30 to 60 minutes prior to the procedure to reduce the risk of infection. Your healthcare provider and an assistant will use an ultrasound to look at the fetal position and the placenta.

Throughout the Test

Once the provider sees where they need to insert the needle, they will clean the skin using an antiseptic and insert the hollow needle into the abdomen. If the placenta is attached to the front of the uterus, the needle will not need to pass through the amniotic fluid.

If it is attached to the back of the uterus, the needle will pass through the amniotic fluid prior to being inserted into the vein in the umbilical cord where it attaches to the placenta. Your healthcare provider will withdraw blood for testing. If no further treatment—such as medication or blood administration—is needed, the needle will be withdrawn and the procedure is complete.

Post Test

Your healthcare provider should monitor the injection site immediately for bleeding. They may want to monitor you for a few hours. Occasionally the fetal heart rate will drop after the PUBS procedure and it will be necessary to continue monitoring to ensure it returns to normal.

After the Test

You should expect test results within a few days to a few weeks depending on the type of testing performed. Once you return home, watch for signs of infection such as:

• Fever
• Redness or swelling, especially around the site where the needle was inserted
• Chills
• Lethargy or feeling sick

Other signs to watch for and call your healthcare provider about include:

• Bleeding from the insertion site
• Early rupture of membranes (water "breaking" too soon)
• Leaking of amniotic fluid
• Vaginal bleeding

Interpreting Results

Because the PUBS procedure is used to diagnose conditions that are often life-threatening to the fetus, waiting for and getting the results can be a time of high anxiety and worry. If your healthcare provider is concerned about a particular diagnosis, it may help to research the diagnosis before the test and while you wait for the results.

However, it is important to get your information from reputable sources. There is a lot of misinformation available and it can cause even greater stress and worry. Ask your healthcare provider to point you towards websites and resources that will provide accurate information.

Make a list of questions for your healthcare provider prior to getting the results so that you make sure you get the information you need. If you receive a particularly difficult diagnosis that shows your baby will have a significant disability or likely not survive, take time to grieve, talk with family and friends, and make an informed decision about how best to handle the situation.

Summary

PUBS is not used to diagnose fetal abnormalities as often as other tests like amniocentesis and CVS, but it is still used in some cases. It can be beneficial and successful in treating blood disorders and fetal hydrops. It is not used as often to diagnose chromosomal abnormalities due to the availability of testing that poses fewer risks.

Undergoing this test can be frightening and stressful for expecting parents. It is likely that your healthcare provider is concerned about a potentially serious condition and you may be faced with difficult decisions after you get the results. If you receive a specific diagnosis, it may help to reach out to families who have also faced the same thing. Your practitioner may be able to provide local resources or you can find groups online that may provide support and assistance.