Cordocentesis — also known as percutaneous umbilical blood sampling — is a highly specialized prenatal test in which a sample of the baby's blood is removed from the umbilical cord for testing.

Cordocentesis can be used to detect certain blood conditions and infections. Cordocentesis can also be used to deliver blood transfusions and medication to a baby through the umbilical cord.

Use of cordocentesis is decreasing, however, since 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.

Cordocentesis might be offered when:

  • The desired information can't be obtained any other way
  • Results from other prenatal tests are unclear
  • Test results might have a significant impact on the immediate management of the pregnancy

Cordocentesis is used primarily to detect and treat blood conditions, such as fetal anemia — a lack of healthy red blood cells in a developing baby.

If you have an infection, cordocentesis might be used to determine whether the baby has the infection, too.

If necessary, cordocentesis can be used to deliver blood transfusions and medication to the baby through the umbilical cord.

Cordocentesis carries potentially serious risks, including:

  • Pregnancy loss. Cordocentesis carries a higher risk of miscarriage than other prenatal diagnostic tests, such as chorionic villus sampling and amniocentesis. Some research estimates the risk as high as 3 percent for the general population. Since many babies are quite ill when the test is done, it's often difficult to determine whether fetal loss is related to the procedure itself or to the baby's health.
  • Bleeding. Bleeding from the area where the needle was inserted is possible.
  • Slowing of the baby's heart rate. The baby's heart rate might slow temporarily after cordocentesis.
  • Infection. Rarely, cordocentesis can lead to a uterine infection.

Ultimately, the decision to have cordocentesis is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.

Before cordocentesis, you can eat and drink as usual.

You might want to ask your partner or another close contact to accompany you to the appointment for emotional support or to drive you home afterward.

Cordocentesis is usually done in an outpatient facility or the health care provider's office, but in some cases it might 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 might 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. Sometimes local anesthetic is used to ease 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.

The entire procedure usually takes about an hour, although most of that time is devoted to the ultrasound exam.

Your baby will naturally replace the small amount of blood that's removed.

Rarely, a blood sample can't be taken from the umbilical cord. In these cases, a blood sample might be taken from a vein in the baby's liver.

After the procedure

After the blood sample is taken, you might experience cramping or a small amount of vaginal bleeding.

Your health care provider might use ultrasound or an external labor monitor to track your baby's heart rate for an hour or two after the procedure.

When you're allowed to 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.

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 a matter of days — or in some cases, within a matter of hours.

Your health care provider or a genetic counselor will help you understand the results of your cordocentesis.

If your test results are normal, follow-up testing isn't usually necessary. However, the circumstances that lead to cordocentesis often need continued intervention.

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

If your test results indicate that your baby has a condition that can't be treated, you might 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.

Oct. 13, 2012