While there is never a good time to acquire a herpes infection, contracting the virus late in pregnancy can prove catastrophic for the newborn child, with a high risk of severe brain damage or death from neonatal herpes.
"Contracting the herpes virus during pregnancy -- especially in the last trimester -- is worse than having herpes going into pregnancy," cautioned Dr. Zane A. Brown, professor of obstetrics and gynecology at the University of Washington. Brown and colleagues publish results of their study in the Aug. 21 issue of The New England Journal of Medicine. Funding is from the National Institutes of Health.
The researchers studied 8,538 pregnant women who received prenatal care at University of Washington Medical Center in Seattle or at Madigan Army Hospital in Tacoma, Wash., between 1989 and 1993. Based on antibody testing in early pregnancy and again at the time of labor, they found that 2 to 3 percent of the women acquired some form of herpes during pregnancy, and that the acquisition was about equally divided among the three trimesters of pregnancy.
The danger to infants exists whether the mother has HSV-1 (oral herpes, the type that produces cold sores) or HSV-2 (genital herpes).
The increased risk to the baby when the virus is acquired late in pregnancy comes because there is insufficient time for the mother to form antibodies to the virus (which takes four to eight weeks) and pass them to the baby before starting labor. With earlier infection, antibodies are passed through the placenta, giving the baby some degree of protection. Without antibodies, the child is highly susceptible to acquiring the virus in the birth canal. With its "naive" immune system, explained Brown, the baby has few resources to fight the virus.
Once infected, babies don't show symptoms for five to 21 days. "Once the baby is symptomatic," said Brown, "it's too late to avert damage, and we're much less likely to contain the infection. Babies have no defenses."
Unlike gonorrhea or syphilis, herpes is not a reportable infection, noted Brown, so there are no national statistics. Estimated rates of neonatal herpes vary throughout the country; in the Northwest, it occurs about once in 2,000 live births; about half of those infants die or suffer brain-damage. "It's treatable, but often undetected, "Brown said. "Mother and baby have usually left the hospital, and the first symptoms are just listlessness and irritability. A couple of days later, there are seizures, but by that time, significant brain damage has occurred.
"In women, there may be no recognizable symptoms," said Brown. "Until now, it was thought that the primary infection brought numerous lesions, headache and flu-like symptoms. But such cases are the tip of the iceberg. About two-thirds of women don't have any idea that they've just gotten herpes; therefore, they're at risk to transmit it to their babies. We have to have some way of diagnosing the mother who's susceptible, and test her partner as well. Even if you can't prevent her from acquiring the infection, at least you know she is at risk."
With routine testing for herpes, said Brown, doctors would know whether to recommend Caesarean delivery to bypass the virus-laden genital tract. Since the baby is at some risk even when it has herpes antibodies from the mother, knowledge of her status would prompt avoidance of some labor and birthing procedures, like foreceps or vacuum delivery that may cause tiny skin breaks through which virus could pass.
Routine testing would also allow care providers to offer counseling on avoiding transmission of herpes between partners. "If you're one of the 20 percent of women who are negative for both HSV-1 and HSV-2," said Brown, "we would recommend that your partner be tested. For example, if he had cold sores (from HSV-1), we would counsel against oral-genital sex during pregnancy."
Brown and his colleagues are calling for regular blood testing for herpes at the first prenatal visit, similar to the testing done to detect other infections and medical problems. They are conducting additional research to evaluate the value of such a program.
"We know when the infection with the virus occurs and when the infection poses the greatest risk to the baby," said Brown. "The question is, can we intervene effectively to lower the risk? We would like to see all pregnant women tested routinely, as they are for German measles and syphilis."