HSV Infection and Pregnancy Outcome

Abstract & Commentary

Synopsis: Two percent or more of susceptible women will develop herpes simplex virus infection during pregnancy, but seroconversion before labor does not appear to adversely affect pregnancy outcome.

Source: Brown ZA, et al. N Engl J Med 1997;337: 509-515.

To determine the frequency of seroconversion for both herpes simplex virus (HSV) types 1 and 2 and the effect of HSV infection on pregnancy outcome, Brown and colleagues determined the antibody status of 7046 susceptible pregnant women at their first prenatal visit, during the second trimester, and during labor. Ninety-four women became seropositive for HSV during pregnancy (1.3%), with 30% of infections occurring in the first trimester, 30% in the second, and 40% in the third. Only 34 women (36%) had symptoms at the time of seroconversion. Of women who were HSV-negative, 30 became HSV-1 positive, and 19 became HSV-2 positive, while 45 women who were HSV-1 positive demonstrated evidence of an infection with HSV-2. None of the women who were HSV-2 positive developed antibodies to HSV-1, suggesting some protection against this infection. A rate of 2.1% was derived for the risk of seroconversion over a 40-week gestation. Almost all of the women who had a symptomatic seroconversion demonstrated genital infections. Six women in this group were delivered by cesarean section because they had active, recurrent genital lesions at the time of birth.

Pregnancy complications such as preterm labor, intrauterine growth restriction, and spontaneous abortion were not increased in the 94 pregnancies in which seroconversion from negative to positive HSV status was demonstrated. None of these 94 pregnancies resulted in an HSV-infected infant, including five who had positive HSV cultures at the time of delivery. An additional nine women were identified who first became infected with genital HSV near the onset of labor. Seven had a primary infection with HSV-2—all of whom were known to have antibodies to HSV-1, and two developed a primary infection to HSV-1 having had no evidence of HSV-2 antibodies in the past. All of these patients had vaginal deliveries. Four of the nine infants became infected with herpes, and two, both in pregnancies complicated by an HSV-2 infection, had serious complications including one neonatal death.

Brown et al conclude that 2% or more of susceptible women will develop HSV infection during pregnancy, but seroconversion before labor does not appear to adversely affect pregnancy outcome. In contrast, women who become infected near the time of labor are at great risk to deliver an infant who will become infected and may develop serious complications.


This important investigation presents data from a large prospective study of women at risk for HSV infection during pregnancy. The study includes some good news and some bad news. First, the good news. Overall, only 2% of women who are susceptible acquire an HSV infection during pregnancy. In those women who developed an antibody response before labor, no increase in adverse pregnancy outcomes was demonstrated including five cases in which genital cultures were positive at the time of delivery. These data suggest that antibodies may protect against HSV transmission. Now, the bad news. In women who acquired an HSV infection around the time of labor and delivery, the risk of neonatal infection was high (4 of 9 infants, 2 of whom developed serious complications). Five of these patients had lesions at the time of labor but did not have a cesarean delivery. Why? In these cases, the lesions were not seen or did not become evident until the postpartum period or the patients presented late in labor and delivered before the diagnosis was made. Can these infections and adverse outcomes be avoided? Serologic testing for HSV late in pregnancy could identify women who lack antibodies to HSV-1 or HSV-2. These patients and their partners could then be counseled to abstain from oral-genital contact or to use condoms during the last trimester.