Pre-pregnancy exposure to cytomegalovirus (CMV), a common herpesvirus that can cause potential risk for pregnant women, can reduce the chances of miscarriage and birth defects, a new study has revealed.

Pregnant women who contract cytomegalovirus are less likely to transmit the infection to their children if they have pre-existing immunity. Researchers at Tulane University made the findings based on a study conducted in macaques.

Cytomegalovirus infection usually does not pose issues in healthy people, and most people do not show any signs of infection. However, pregnant women and people with weakened immune systems might develop complications.

CMV is a leading cause of miscarriage and birth defects, including cerebral palsy and hearing loss, in children. The infection spreads through body fluids, such as blood, saliva, urine, semen and breast milk.

According to the Centers for Disease Control and Prevention (CDC), 20% of children born with congenital cytomegalovirus infection will have long-term health problems. They may include growth issues, neurologic defects and issues with the brain, liver, spleen, and lungs.

Although the risk posed by CMV to a pregnant woman who gets the infection for the first time during pregnancy was known, the mechanism by which pre-existing immunity reduces their vulnerability was not fully understood until now. The researchers of the latest study identified the specific immune mechanisms responsible for the protective effect.

"When pregnant mothers were initially infected with CMV during the first trimester, all of them transmitted the virus to their offspring, resulting in a high rate of miscarriage. However, when nonhuman primates previously infected with CMV were reinfected during their pregnancies, their offspring were protected. The robust immune response observed in mothers upon reinfection resulted in only one out of five mothers passing the virus through the placenta, with no adverse health outcomes for any of the infants," the researchers said in a news release.

They emphasized that the nonhuman primate model used for the research closely resembled human CMV infection and transmission. They believe the study is a significant step toward finding a vaccine to prevent infection in mothers and babies.

"Understanding how pre-existing immunity can protect against CMV transmission during pregnancy is crucial for developing an effective CMV vaccine that can safeguard all pregnant women and their unborn babies," said Dr. Amitinder Kaur, principal investigator of the study.