Cordocentesis : Percutaneous Umbilical Blood Sampling (PUBS)

Cordocentesis, also sometimes called Percutaneous Umbilical Cord Blood Sampling (PUBS), is a diagnostic test which examines blood from the fetus to detect fetal abnormalities. Use of cordocentesis is becoming rare because diagnostic procedures such as amniocentesis and chorionic villus sampling, which pose a lower risk of fetal death, can be used instead for prenatal diagnosis of disease.

How is cordocentesis performed?

About 30 to 60 minutes before the procedure, you might be given antibiotics to reduce the risk of a uterine infection. This is usually done through a tube inserted into a vein.

Your health care provider will use ultrasound to determine the umbilical cord’s location in your uterus. You’ll lie on your back on an exam table, and your health care provider will apply a special gel to your belly. He or she will then use a small device known as an ultrasound transducer to show your baby’s position on a monitor.

Next, your health care provider will clean your belly. Sometimes medication is given to prevent discomfort during the procedure, but often it isn’t needed.

Guided by ultrasound, your health care provider will insert a thin, hollow needle through your abdominal wall and into your uterus. A small amount of blood from the vein in the umbilical cord will be withdrawn into a syringe, and the needle will be removed.

You’ll need to lie still while the needle is inserted and the blood is withdrawn. You might notice a stinging sensation when the needle enters your skin, and you might feel cramping when the needle enters your uterus.

After the procedure

After the blood sample is taken, you might have cramping or a small amount of discomfort.

Your health care provider will use an ultrasound or an external labor monitor to track your baby’s heart rate after the procedure.

When you go home, your health care provider might suggest resting for the remainder of the day. You’ll likely be able to resume normal activities the next day. Call your health care provider if you experience vaginal bleeding or fluid leakage.

The blood sample will be analyzed in a lab. Test results are typically available within days.

When is cordocentesis performed?

Cordocentesis is usually done when diagnostic information cannot be obtained through amniocentesis, CVS, or ultrasound, or if the results of these tests were inconclusive. Cordocentesis is performed after 17 weeks of pregnancy.

What does the test look for?

Cordocentesis detects chromosome abnormalities (i.e. Down syndrome) and blood disorders (i.e. fetal hemolytic disease.).

Cordocentesis may be performed to help diagnose any of the following concerns:

  • Malformations of the fetus
  • Fetal infection (i.e. toxoplasmosis or rubella)
  • Fetal platelet count in the mother
  • Fetal anemia
  • Isoimmunisation

This test is different from amniocentesis in that it does not allow testing for neural tube defects.

What do cordocentesis results mean?

Cordocentesis is a diagnostic test that detects chromosome abnormalities and certain blood disorders with high levels of accuracy. Although the probabilities of identification are high, this test does not measure the severity of these disorders. This test also does not help identify neural tube defects.

What are the risks and side effects to the mother or baby?

Although cordocentesis is considered a safe procedure, it is recognized as an invasive diagnostic test that carries a higher risk of complications to the baby, including death, than other procedures do. Your health care provider will offer the procedure only if other options aren’t available or they won’t produce results quickly enough. Miscarriage is the primary risk related to cordocentesis, occurring -1-2 times out of every 100 procedures.

Other potential side effects include:

  • Blood loss from the puncture site
  • Infection
  • Drop in fetal heart rate
  • Premature rupture of membranes
  • Infection

Contact your healthcare provider if these symptoms remain or get worse.
You should also contact your healthcare provider if you experience:

  • Fever
  • Chills
  • Leaking of amniotic fluid

What are the reasons to test or not test?

The reasons to test or not vary from person to person, couple to couple, and physician to physician.
Performing the tests and confirming the diagnosis provides you with certain opportunities:

  • Pursue potential medical interventions that may exist
  • Begin planning for a child with special needs
  • Start addressing anticipated lifestyle changes
  • Identify support groups and resources

Some individuals or couples may elect not to pursue testing or additional testing for various reasons:

  • They are comfortable with the results no matter what the outcome is
  • Because of personal, moral, or religious reasons, making a decision about carrying the child to term is not an option
  • Some parents choose not to allow any testing that poses any risk of harming the developing baby

It is important to discuss the risks and benefits of testing thoroughly with your healthcare provider. Your healthcare provider will help you evaluate if the benefits from the results could outweigh any risks from the procedure.

Want to Know More?

Compiled using information from the following sources:

1. Danforths Obtsetrics and Gynecology Ninth Ed. Scott, James R,et al, Ch.6

2. William’s Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 13.

3. Mayo Clinic