Percutaneous umbilical blood sampling

Percutaneous umbilical blood sampling (PUBS) is a highly specialized prenatal test in which a blood sample is removed from the umbilical cord and tested for genetic problems or infections. Percutaneous umbilical blood sampling can provide important information about your baby’s health. It’s not a common test, however. It’s typically offered only when the test results may have a significant impact on the management of the pregnancy. Percutaneous umbilical blood sampling can be done after the 18th week of pregnancy.

Percutaneous umbilical blood sampling carries about a two in 100 risk of miscarriage. Still, the test can play an important role in prenatal care. A key benefit is speed. Results are usually available within 72 hours — in some cases, in as little as two hours. Also, percutaneous umbilical blood sampling can be used to deliver blood transfusions and medication to the baby through the umbilical cord.

Percutaneous umbilical blood sampling is also known as umbilical vein sampling, fetal blood sampling and cordocentesis. Specifically, percutaneous umbilical blood sampling can be used to identify:

  • Chromosomal conditions. Percutaneous umbilical blood sampling can be used to diagnose chromosomal conditions, such as Down syndrome.
  • Blood disorders. Percutaneous umbilical blood sampling can be used to detect various blood disorders, including anemia, sickle cell disease and hemophilia. The test can also determine whether the baby has Rh positive or Rh negative blood. If your blood is Rh negative and your baby’s blood is Rh positive, your body may make antibodies that attack the baby’s red blood cells.
  • Infections. If you have an infection, such as toxoplasmosis or rubella, percutaneous umbilical blood sampling may be used to determine whether the baby has the infection, too.
  • Restricted growth. Sometimes percutaneous umbilical blood sampling is used to determine why a baby isn’t growing as expected.

Percutaneous umbilical blood sampling
Percutaneous umbilical blood sampling can’t be used to test for neural tube defects, such as spina bifida.

Sometimes percutaneous umbilical blood sampling is used to supplement the results from other diagnostic screenings and tests, such as ultrasound. This procedure can also be used to deliver blood transfusions and medication to the baby through the umbilical cord. Use of percutaneous umbilical blood sampling is decreasing, however. Newer forms of technology can sometimes provide the same information from tests that pose a smaller risk of miscarriage, such as amniocentesis or chorionic villus sampling.

Percutaneous umbilical blood sampling carries various risks, including:

  • Miscarriage. Percutaneous umbilical blood sampling carries about a two in 100 risk of miscarriage. This is higher than the risk of miscarriage associated with other prenatal diagnostic tests, such as chorionic villus sampling and amniocentesis.
  • Bleeding. Bleeding from the needle entry site is possible.
  • Slowing of the baby’s heart rate. The baby’s heart rate may slow temporarily after percutaneous umbilical blood sampling.
  • Infection. Rarely, percutaneous umbilical blood sampling may cause a uterine infection.

Remember, percutaneous umbilical blood sampling is offered when the test results may have a significant impact on the management of the pregnancy. Ultimately, the decision to have percutaneous umbilical blood sampling is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.

Percutaneous umbilical blood sampling is usually done in an outpatient facility or the health care provider’s office, but in some cases it may be done in the hospital. At least one assistant will likely help your health care provider during the procedure.

During the procedure
About 30 to 60 minutes before the procedure, you may be given antibiotics to reduce the risk of a uterine infection.

When the procedure begins, your health care provider will use ultrasound to determine the baby’s exact 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 abdomen. 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 abdomen with an antiseptic. Generally, anesthetic isn’t needed. Most women report only mild discomfort during the procedure.

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 may notice a stinging sensation when the needle enters your skin, and you may feel cramping when the needle enters your uterus. The entire procedure usually takes about an hour, although most of that time is devoted to the ultrasound exam. Your baby’s body will naturally replace the small amount of blood that’s removed.

After the procedure
After percutaneous umbilical blood sampling, your health care provider may use ultrasound to monitor your baby’s heart rate. You may experience cramping or a small amount of vaginal bleeding immediately after the blood sample is taken. Your health care provider may suggest resting after the procedure. You may want to ask someone to drive you home. You’ll likely be able to resume normal activities the next day.

If you experience fever, chills or vaginal bleeding, contact your health care provider right away.

Meanwhile, the blood sample will be analyzed in a lab. Test results are typically available within 72 hours. Your health care provider or a genetic counselor will help you understand the results of your percutaneous umbilical blood sampling.

If your test results are normal, follow-up testing isn’t usually necessary.

If your baby has an infection, your health care provider will help you understand the treatment options. If your baby has severe anemia, he or she may need a blood transfusion through the umbilical cord. In some cases, labor is induced early.

If your test results indicate that your baby has a chromosomal problem or a hereditary condition that can’t be treated, you may be faced with wrenching decisions — such as whether to continue the pregnancy. Seek support from your health care team, your loved ones and other close contacts during this difficult time.