The chances of a baby being born with herpes are increased when the father is younger than 20 or whose age is unknown, and when the mother is younger than 25, Seattle researchers report.

However, they say, using parents’ age to help target pregnancies for herpes testing would still miss a “substantial proportion” of newborn herpes cases.

Most cases of neonatal herpes occur in infants born to women with no history of genital herpes, Dr. Karen E. Mark of the University of Washington, Seattle, and colleagues note.

Testing for the herpes simplex virus (HSV) during pregnancy and at delivery could help identify these women, the researchers note, and timely treatment would prevent their babies becoming infected.

Identifying risk factors for having an infant with neonatal herpes could boost the cost-benefit of screening. To that end, the researchers looked at data for all live births in Washington state from 1987 to 2002, which included 91 cases of neonatal HSV. In 74 percent of these cases there was no known maternal history of genital herpes.

Maternal age younger than 25 increased the likelihood of the baby being born with herpes by 1.9-fold, and paternal age younger than 20 or unknown paternity increased the risk 1.7 times.

Based on these criteria, 36 percent of all pregnancies would need to be screened, but doing so would prevent 60 percent of neonatal herpes cases, the researchers report in the American Journal of Obstetrics and Gynecology.

Fever during labor and premature membrane rupture were also tied to cases of newborn herpes, the researchers found. Screening for these factors, along with maternal history of genital herpes, would require 60 percent of all pregnancies be screened and would identify 84 percent of cases.

Cost analyses have found that screening of all pregnant women for herpes would be “prohibitively expensive,” costing $363,000 to $1,000,000 for every case of neonatal HSV prevented, Mark and her colleagues note.

Their suggestion to screen only women younger than 25 or those whose partners were under 20 or of unknown age “would cost approximately one third as much and provide two thirds the benefit,” they point out. “Clinicians, payers, policymakers and the public will have to weigh these findings in deciding what approach to prevention is desirable.”

SOURCE: American Journal of Obstetrics and Gynecology, February 2006.