Skip to Content


Medically reviewed on Oct 8, 2018


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

Cordocentesis is usually done after week 18 of pregnancy. The test can be used to detect certain genetic disorders, blood conditions and infections. Cordocentesis can also be used to deliver blood transfusions or medication to a baby through the umbilical cord.

Use of cordocentesis is decreasing. This is because diagnostic procedures such as amniocentesis and chorionic villus sampling, which pose a lower risk of fetal loss, can be used in place of cordocentesis for prenatal diagnosis of disease. However, cordocentesis might be offered if other prenatal tests don't provide enough or sufficiently timely diagnostic information.


Cordocentesis, also known as percutaneous umbilical blood sampling (PUBS), is a diagnostic prenatal test. During cordocentesis, an ultrasound transducer is used to show the position of the fetus and umbilical cord on a monitor. Then a fetal blood sample is withdrawn from the umbilical cord for testing.

Why it's done

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

Cordocentesis is usually done when a diagnosis can't be obtained from amniocentesis, chorionic villus sampling, ultrasound or other methods. Because cordocentesis carries a higher risk of fetal loss than these other methods your health care provider will only offer the procedure if other options are not available or they won't produce timely results.

In rare situations, cordocentesis might be used to check the shape and number of fetal chromosomes (karyotype analysis). Fetal blood karyotyping can be done within 48 hours, possibly providing results quicker than amniocentesis or chorionic villus sampling.


Cordocentesis carries potentially serious risks, including:

  • Fetal Bleeding. Bleeding from the area where the needle is inserted is the most common complication of cordocentesis. If life-threatening fetal bleeding occurs, your health care provider might recommend replacement of blood products to the fetus.
  • Cord hematoma. A collection of fetal blood within the cord might occur during or after a cordocentesis. Most babies don't have symptoms when this occurs. However, a few might develop a low heart rate for a short period of time. If the hematoma is stable, your health care provider will observe the baby. If the hematoma is not stable or if your baby's heart rate doesn't recover, your health care provider will recommend an emergency C-section.
  • 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 or fetal infection.
  • Fetal-maternal bleeding. Fetal blood might enter maternal circulation in about 40 percent of procedures. The amount of bleeding is usually small. This problem is more common when the placenta lies in the front of the uterus.
  • Pregnancy loss. Cordocentesis carries a higher risk of fetal loss than other prenatal diagnostic tests, such as chorionic villus sampling and amniocentesis. The risk is about 1.4 to 1.9 percent for a fetus that appears normal and is being tested for genetic disorders. However, 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.

Ultimately, the decision to have cordocentesis is up to you. Your health care provider and a genetic professional can help you weigh all the factors in your decision.

How you prepare

If you are about 24 weeks pregnant, you will be asked to avoid eating or drinking after midnight the night before cordocentesis. This is because certain complications caused by the procedure might require an emergency C-section. Ask your health care provider for guidance.

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.

What you can expect

Before week 24 of pregnancy, cordocentesis is usually done in an outpatient facility or the health care provider's office. After week 24 of pregnancy, cordocentesis is usually done in the hospital. At least one assistant will likely help your health care provider during the procedure.

A sample of your blood will be taken before the procedure for comparison with the fetal blood samples.

During the procedure

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 an intravenous catheter.

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.

After the procedure

After the blood sample is taken, you might experience 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. Your health care provider will ask you to contact him or her if you experience signs or symptoms such as vaginal bleeding or fluid leaking.

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


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

If your test results are normal, your health care provider will share with you information regarding follow-up appointments.

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 might need a blood transfusion through the umbilical cord.

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.

© 1998-2018 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. Terms of use