How Common is Herpes Among Pregnant Women?

Herpes Virus, artwork
Herpes Virus, artwork. David Mack/Science Photo Library/Getty Images

Despite the overpowering stigma associated with herpes infection, for most people it's not much of a medical concern. In fact, the vast majority of people with herpes infections never know they're infected, as many infections are either asymptomatic or unrecognized.

In fact, the major medical concern about herpes infections is what happens with the virus during pregnancy and childbirth. Neonatal herpes infections can be quite dangerous, and even deadly.

Mortality rates for neonatal herpes infections may be as high as 40 percent. Fortunately, the incidence of these infections is relatively low, and women are primarily considered to be at risk when they become infected during pregnancy. The risk is much lower if the primary infection occurs earlier in life and the infection is chronic when the woman becomes pregnant, even if she has outbreaks during the pregnancy or near the time of birth.

That's a very good thing indeed, because research has shown that herpes infections are incredibly common during pregnancy. According to a research study that examined herpes seroprevalence in over 15,000 women who gave birth at an academic medical center in Seattle between 1989 and 2010, and almost 19,000 pregnancies, the majority of women are infected with HSV-1 -- more than 65 percent. This percentage was much higher in African American, Hispanic, and Asian women than their White counterparts, reaching over 90 percent during some years.

Interestingly, while the percentage of women infected with HSV-1 declined only slightly over the study period -- from 69 to 65 percent -- the percentage of women infected with HSV-2 dropped precipitously. It declined by almost half -- from 30 to 16 percent.

Looking at pregnancies, instead of women, 76 percent were positive for at least one form of HSV.

Fifty-three percent were positive for HSV-1 alone, 15 percent for HSV-1 and HSV-2, and 9 percent for only HSV-2. However, despite the large numbers of pregnancies where women were infected with herpes, neonatal herpes infections were relatively rare.

Interestingly, there may be one downside to the decline in genital herpes infections seen in pregnant women over the last decade. Since new infections during pregnancy carry the most risk of causing fetal problems, if a woman is going to be infected with genital herpes it's better if that infection happens before pregnancy rather than during pregnancy. Fewer women becoming infected prior to a first pregnancy means that there's a larger proportion who carries the risk of becoming infected during that pregnancy. Although ideally they won't become infected at all, this is a risk that doctors and couples need to be aware of. It may potentially be an issue even for monogamous couples, as STD transmission doesn't occur every time people have sex, so someone may have gotten pregnant by a herpes infected partner without picking up the virus.

Sources

Corey L, Wald A. Maternal and neonatal herpes simplex virus infections. N Engl J Med. 2009 Oct 1;361(14):1376-85. doi: 10.1056/NEJMra0807633. Erratum in: N Engl J Med. 2009 Dec 31;361(27):2681.

Delaney S, Gardella C, Saracino M, Magaret A, Wald A. Seroprevalence of herpes simplex virus type 1 and 2 among pregnant women, 1989-2010. JAMA. 2014 Aug 20;312(7):746-8. doi: 10.1001/jama.2014.4359. PubMed PMID: 25138337; PubMed Central PMCID: PMC4414330.

James SH, Kimberlin DW. Neonatal herpes simplex virus infection: epidemiology and treatment. Clin Perinatol. 2015 Mar;42(1):47-59, viii. doi: 10.1016/j.clp.2014.10.005.

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