What you can expect

Before week 23 of pregnancy, cordocentesis is usually done in an outpatient facility or the health care provider's office. After week 23 of pregnancy, cordocentesis is usually done in the hospital, in case the baby develops complications that might require an emergency delivery.

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 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 A small amount of blood from the vein in the umbilical cord will be withdrawn into a syringe, and the needle will be removed.

You'll need to lie still while the needle is inserted and the blood is withdrawn.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.