Women of reproductive age have the greatest incidence of genital herpes simplex virus (HSV) infections, and 85% of neonatal HSV infection results from viral transmission during labor and delivery. The American College of Obstetricians and Gynecologists recommends that women with genital HSV lesions undergo cesarean section to prevent the spread of HSV to infants.

Now there may be a better way. Researchers at the University of Texas Southwestern Medical Center in Dallas followed 350 pregnant women who either had a history of HSV outbreaks or developed outbreaks while pregnant. After taking the antiviral drug valacyclovir during their last month of pregnancy, they had fewer HSV infections and fewer cesarean deliveries.

Starting at 36 weeks' gestation, half of the participants took valacyclovir 500 mg twice daily; the others took placebo. At the time of delivery, just 4% of the valacyclovir group (seven of 170) had active HSV lesions that dictated cesarean deliveries; 13% of the placebo group (21 of 168) did. No infants exposed to valacyclovir showed adverse effects, such as anemia, at one month, and none of the infants born to any of the women tested positive for HSV.

While the drug's safety for both mother and fetus earlier in pregnancy has not been examined, the authors conclude that antiviral therapy starting at 36 weeks' gestation should be considered. They estimate that treating just 11 HSV-positive women with valacyclovir could prevent one cesarean delivery.

Carol Potera