In a new study, researchers found that the longtime practice of performing a cesarean section in women who have active herpes infections does indeed reduce the risk that their newborns will be infected with the virus. The study also found that women who had been infected with herpes relatively recently were more likely to pass on the virus to their babies than women who had been infected for a longer time.

The "bottom line" of the research, lead investigator Dr. Zane A. Brown told Reuters Health, "is that we have to prevent women from acquiring genital herpes during pregnancy to prevent the newborn from acquiring neonatal herpes."

To do this, doctors should use a blood test to screen pregnant women for genital herpes the first time they seek prenatal care, according to Brown, who is at the University of Washington in Seattle.

"If they are found to be susceptible, then we must test their partners," Brown said. If there is a chance that a woman can be infected by her partner, then doctors should advise the woman on how to protect herself, according to the Seattle researcher. This may include abstaining from sex during pregnancy, using condoms or having her partner use an antiviral drug such as acyclovir, Brown said.

Though symptoms of herpes, particularly genital herpes, can be extremely painful, infection with the herpes simplex virus, or HSV, is generally not life-threatening in adults. When a child becomes infected with HSV, often after being exposed to genital secretions during delivery, the infection can be deadly if it is not treated. HSV infection may cause brain damage in children who survive.

One type of herpesvirus, HSV-1, usually infects the mouth and causes cold sores on the mouth and face. Another type, HSV-2, most often causes sores on and around the genitals.

Both HSV-1 and HSV-2 may be present in the birth canal, so infection with either type may put newborns at risk.

For women who have herpes sores on their genitals during pregnancy, a C-section is usually recommended to reduce the risk of transmission during birth. There is little evidence on whether this practice reduces infant herpes infections, however.

Now, Brown and his colleagues report that cesarean delivery can indeed reduce a woman's risk of passing on HSV to her child.

In a study of 202 pregnant women who were infected with HSV at the time of delivery, only about 1% of women who had a C-section gave birth to a child with HSV, compared with nearly 8% who delivered vaginally.

A report on the study appears in the January 8th issue of the Journal of the American Medical Association (news - web sites).

Brown's team identified several other factors that affected the transmission of HSV. Women who had been recently infected, meaning their bodies had not had enough time to produce antibodies to HSV in the blood, were most likely to pass on the infection during birth. This risk, according to the report, reflects the fact that these women's infants lacked antibodies of their own to ward off HSV.

The study also found that women who had been previously infected with HSV-2 had a very low or nonexistent risk of passing on either HSV-1 or HSV-2 during birth.

A woman's care during labor also seemed to have a large impact on the risk of spreading HSV, according to the report. Infants whose mothers had undergone invasive monitoring tests as they prepared to give birth were more likely to be born with HSV.

SOURCE: Journal of the American Medical Association 2003;289:203-209.