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# Study: Herpes Drugs Don't Cause Birth Defects
- URL: https://www.foodconsumer.org/study_herpes_drugs_don_t_cause_birth_defects_082520100328/
- Published: 2010-08-25T16:25:00.000Z
- Updated: 2026-09-22T16:03:25.000Z
- Description: Antivirals such as acyclovir, valacyclovir and famciclovir reduce the severity and duration of herpes symptoms and can suppress outbreaks, but their safety in the first trimester of pregnancy is poorly documented. About 2 in 1,000 US pregnancies are exposed to them in the first trimester.
- Author: Laura King
- Tags: Drug, Health News, #vivvo-import

New Study Reveals Herpes Drugs Don't Cause Birth Defects

The most common types of the Herpes Simplex Virus (HSV) are: type 1 oral herpes (HSV-1), causing sores around the mouth and lips referred to as fever blisters or cold sores; type 2, genital herpes (HSV-2) causing sores around the genitals or rectum or other locations below the waist; Herpes Zoster Virus causing chickenpox and shingles.

There is no cure for HSV-1, HSV-2 or Herpes Zoster all of which are highly contagious. Once a person has the virus, it remains in the body, inactive in the nerve cells, until something triggers it to become active again. WebMD reports "At least 50 million persons in the United States have HSV-2." 

Treatment using antiviral drugs including acyclovir, valacyclovir, and famciclovir reduce the severity and duration of symptoms and can suppress outbreaks. Safety of these antivirals when used in the first trimester of pregnancy have not been sufficiently documented.

Twenty-two percent of pregnant women are seropositive for HPV1 and 2% of susceptible pregnant women acquire a primary herpes simplex virus infection. The incidence of herpes zoster rises between ages 30 and 40 during which many women are starting their families. Given this background, antiviral treatment will be indicated for a significant number of women in pregnancy, and while it is believed that these drugs are safe for use during that time, research thus far has been extremely scarce.

"The Slone Epidemiology Center, Boston, Massachusetts, statistics on normal pregnancies indicate that approximately 2 per 1000 pregnancies are exposed to antiviral drugs during the first trimester." (A. Mitchell and C. Louik, Slone Epidemiology Center at Boston University, written communication, July 14, 2010). "Thus, each year in the United States approximately 15 000 conceptuses are potentially exposed to these drugs, yet little information is available on their teratogenicity."

Published today in the Journal of American Medical Association (JAMA), a study funded by the Danish Medical Research Council and the Lundbeck Foundation led by Dr. Bjorn Pasternak, Department of Epidemiology Research, Statens Serum Institute in Copenhagen reveals that pregnant women who take antiviral drugs against the herpes virus should not worry that their use will cause birth defects.

“Our study, to our knowledge the largest of its kind, found no significant association between first-trimester exposure to antiherpetic antiviral drugs and major birth defects." says study authors.

The study contains data from 1996 to 2008 on almost 840,000 births to women without chromosomal abnormalities, genetic syndromes, birth defect syndromes, or congenital viral infections.

Results revealed that, "Among 1804 pregnancies exposed to acyclovir, valacyclovir, or famciclovir in the first trimester, 40 infants (2.2%) were diagnosed with amajor birth defect compared with 19 920 (2.4%) among the unexposed," causing Pasternak and colleagues to conclude that the antiviral drugs were not associated with birth defects.

Authors noted "Acyclovir is the most extensively documented antiviral and should therefore be the drug of choice in early pregnancy, while data on valacyclovir and famciclovir are still insufficient. Future research on antiherpetic antivirals and mother-child health should include safety studies with regard to spontaneous abortion and preterm birth, and during breastfeeding."

Pregnant women with genital herpes should be careful about passing the virus on to the baby, during delivery, which can be fatal. Women with HPV-2 are examined carefully for any signs of sores or other symptoms signaling an outbreak at the time of delivery making it necessary to for the baby to be delivered by cesarean section.

If infected early in pregnancy or a woman was HPV-2 prior to pregnancy, the risk is less than 1% that it will be passed to her baby because antibodies against the virus have formed helping to protect the baby. The risk raises significantly, 30-50%, when a woman is newly infected late in pregnancy due to the fact that the mother's immune system has not developed protective antibodies against the virus. It is imperative that you tell your doctor immediately if you are pregnant and have been exposed to HPV-2 or think you have been infected recently.

Outbreak causes:

 \*General illness  
 \*Fatigue  
 \*Physical or emotional stress  
 \*Menstruation  
 \*Trauma to the affected area, including sexual activity  
 \*Immunosuppression due to AIDS, chemotherapy or steroids