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Cytomegalovirus (Amniotic Fluid)

Does this test have other names?


What is this test?

This test checks a developing baby for cytomegalovirus (CMV), a virus that belongs to the herpes family of viruses. The herpes family includes herpes simplex; varicella zoster, which causes chickenpox and shingles; and Epstein-Barr mononucleosis. 

Cytomegalovirus is common in adults and even children. Between 50 and 80 percent of all adults will have CMV by the time they’re 40. It usually goes undetected because actual symptoms are rare. Most symptoms you could experience are relatively mild and flu-like.

Once you contract the virus, you’ll always carry it in a dormant, or nonactive, state and produce antibodies to keep the virus in check. CMV can “shed,” or makes its way into the environment, even without your having any symptoms.

CMV is spread in two ways. You can catch it through contact with the bodily fluids of an infected person who’s shedding, and it can be transferred from a woman to her unborn baby during pregnancy or childbirth, and to her newborn while breastfeeding. The greatest concern is when a woman contracts CMV for the first time during pregnancy. The infection is passed to the baby about one-third to one-half of the time and can pose a health threat in up to 15 percent of these babies, even if they don’t have symptoms at birth. 

CMV in a newborn can later lead to:

  • Hearing loss

  • Vision loss

  • Learning disabilities

  • Slightly enlarged liver and spleen

  • Small red spots on the skin

  • Eye problems

  • Seizures

If you had CMV before becoming pregnant and it becomes active again, you could still infect your unborn baby, but the chances are much lower – only about 1 percent. Of those infected babies, only 1 to 10 percent will have symptoms at birth, and up to 15 percent may later develop CMV disease symptoms.

Doctors can check for cytomegalovirus in several ways. To check for it in an unborn baby, the test is done on amniotic fluid, the fluid in the amniotic sac, where the baby is developing. The procedure used to get a sample of amniotic fluid is called amniocentesis. The amniotic sample will be put in a special dish with a substance that will encourage the virus to grow, if it exists in the sample.

Why do I need this test?

You might need this test if you are pregnant and have symptoms similar to mononucleosis. Symptoms include:

  • Prolonged fever

  • Sore throat

  • Fatigue

  • Achiness

  • Swollen glands

You might also have this test if you have too little amniotic fluid, a possible sign of CMV.

What other tests might I have along with this test?

Your doctor may also order other tests of your amniotic fluid. The fluid can be checked for other serious health conditions, including chromosome abnormalities that could mean Down syndrome, genetic disorders like cystic fibrosis, and neural tube defects such as spina bifida. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal results are negative, meaning that CMV wasn’t found. Positive results mean that your developing baby has been exposed to CMV.

If your results are positive, your newborn will be given either a saliva swab or urine culture test within the first two to three weeks of life. If your newborn tests positive for CMV, your child’s health care provider will closely watch the baby’s hearing, vision, and brain development. You may also want to discuss the possibility of antiviral drugs for the infant.

How is this test done?

This test requires a sample of amniotic fluid. The sample is collected during a procedure called amniocentesis. It is usually done in a medical office.

In this procedure you lie down on an examination table, and a health care professional uses an ultrasound machine project an image of your unborn baby onto a monitor. These images pinpoint where to draw the fluid sample without touching the fetus.

A health care provider applies local anesthetic to your abdomen then injects a needle to draw out a small sample of amniotic fluid. Collecting the sample of fluid usually only takes about five minutes, but you may be at the facility for 45 minutes or longer.

Does this test pose any risks?

Amniocentesis is considered a safe procedure, but you have a one in 300 to 500 chance that you may miscarry. Miscarriages can happen if you develop an infection in your uterus, if your water breaks prematurely, or if you go into early labor.

It's extremely rare for the baby to come into contact with the needle. The health care providers watch the monitor very closely.

After the procedure, you may feel cramping, leak a little fluid or blood from your vagina, or feel discomfort around the puncture site. If any of these symptoms persist or get worse, or if you develop a fever, call your health care provider right away. Ask your doctor if you should avoid certain activities after the procedure.

What might affect my test results?

Taking either antiviral medications or drugs that suppress your immune system will affect your results. Because of this, if you take these drugs, you may not be able to have this test.

How do I get ready for this test?

Make sure to tell the health care provider if you are taking antiviral medications, even if it’s for something common like cold sores. In addition, be sure your doctor knows about all other medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don’t need a prescription and any illicit drugs you may use.