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What is CMV?

CMV, or Cytomegalovirus is a herpes virus that generally leads to a benign viral illness in healthy children and adults. Similar to other herpes viruses, CMV is capable of remaining latent in the body and returning years later.

A CMV infection is caused by immediate contact with an infected person’s saliva, urine, or other body fluids. This infection is common in households with small children or daycare centers. Approximately 50% of women of reproductive age have antibodies to CMV in their blood, demonstrating prior exposure to this virus.  Currently, there is no vaccine for this virus.

Vertical Transmission of CMV

Unlike most other viruses, CMV acquired during pregnancy can cross the placenta and infect the fetus, potentially causing harm. These infections during pregnancy are classified as either primary where the infection is acquired during pregnancy or secondary where CMV is reactivated during pregnancy from a prior infection. The risk of fetal infection is significantly higher with primary infection compared to secondary infection (40% vs. less than 1%).

If fetal infection occurs, approximately 80 to 90% of infected newborns do not show symptoms at birth. However, the likelihood of long-term conditions in these asymptomatic babies, including hearing loss or developmental delay, is approximately 15%.

The 10 to 20% of infected newborns who do show symptoms at birth are at a much higher risk of mortality and long-term morbidity. About two-thirds of these babies will have neurologic involvement. Symptoms at birth may include growth restriction, hemolytic anemia, hepatitis, thrombocytopenia, and intracranial calcifications.

CMV may be transmitted during delivery or through breastfeeding, but these transmissions are much less likely to cause long-term problems in the newborn, except in preterm babies.

Diagnosis of CMV during Pregnancy

Cytomegalovirus is either diagnosed after an abnormal ultrasound that leads to CMV testing, or after a routine serologic testing that reveals certain anti-CMV antibodies. Serologic testing is not routinely recommended for women without symptoms or at low-risk as there are many results that lead to false scares and unnecessary testing.

If testing is positive after an abnormal ultrasound finding, the prognosis is generally worse since there is already evidence that the fetus may be affected. However, ultrasound results may suggest, but not diagnose or exclude, CMV infection in the fetus. These findings include ventriculomegaly, microcephaly, echogenic bowel, fetal growth restriction, hepatosplenomegaly, ascites, intracranial calcifications, and placental enlargement.

Treatment and Prevention of CMV during Pregnancy

Antiviral medication is rarely indicated in pregnant women with CMV since it has not shown to reduce the risk of vertical transmission. Hyperimmunoglobulin therapy (IVIG) is a potential approach to decrease the risk and complications from vertical transmission of this virus but is still investigational. In a prospective study, IVIG was associated with a reduced risk of symptomatic CMV in newborns. A follow-up case study on three-year-old children showed a similar benefit to IVIG.

However, a recent randomized trial did not demonstrate significant benefits to IVIG. The overall rate of congenital infection was similar in both the control and treated groups, as was the proportion of infected infants with symptoms at birth. Treatments and prevention are discussed with patients with CMV, but research on clear benefits of these strategies are ongoing.

Maternal Fetal Medicine blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!