The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

This medication is considered to have a low risk when used during pregnancy:

Although human data is limited, acyclovir is not thought to cause any birth defects. The manufacturer recommends using acyclovir only in pregnant women who have a clear need for therapy.

What is acyclovir?

Acyclovir is an antiviral medication that is used to treat herpes virus infections.

What is acyclovir used to treat?

Acyclovir is a prescription medication used to treat herpes, shingles, and chickenpox. It is indicated for treatment of genital herpes in pregnant women. Acyclovir is also used to treat herpes infections in infants and children.

How does acyclovir work?

Acyclovir stops the cell division of a virus so that it can not spread in the body.

If I am taking acyclovir, can it harm my baby?

It is estimated that 1 out of every 7500 U.S. births involves acyclovir exposure in the baby. A study of data collected from 2001 to 2007 found that the exposure rate to acyclovir during pregnancy may be 3%, with most instances of exposure occurring after the first trimester.

Usual doses of acyclovir have not been associated with any birth defects in animal studies; however, changes in the immune system of the baby, development of the baby, and changes to chromosomes in the baby were noted in some animals studies. Acyclovir does cross the human placenta to reach the developing baby. Case reports and registry data in humans do not show an association between acyclovir use during pregnancy and harm to the baby. A registry that compiled data from 1984 to 1999 in pregnant women with first trimester exposure to acyclovir reported that birth defect rates were similar to rates in the general U.S. population. Some studies have found a connection between acyclovir use in pregnancy and infant abdominal wall defects, but evidence is not conclusive. Acyclovir therapy in pregnant mothers can reduce virus transmission, and acyclovir can reduce the risk of associated premature birth and infant herpes infection often seen with active maternal infection.

If I am taking acyclovir and become pregnant, what should I do?

Pregnant women who have genital herpes infections should talk to their doctor to weigh the risks versus benefits of acyclovir therapy during pregnancy. Acyclovir is only recommended during pregnancy if the benefits outweigh the risks of therapy.

If I am taking acyclovir, can I safely breastfeed my baby?

The American Academy of Pediatrics has stated that acyclovir is safe to use in breastfeeding women. Acyclovir is found in breast milk, but it is not expected to cause harm to an infant. The average dose ingested by breastfeeding infants is 1%-2% of the mother's dose. Mothers with herpes lesions on or near the breast should avoid breastfeeding to prevent virus transmission to their baby.

If I am taking acyclovir, will it be more difficult to get pregnant?

Animal studies have found that high doses of acyclovir can harm male testis and sperm development. Human studies have not shown any negative effects on sperm production in males.

If I am taking acyclovir, what should I know?

Although evidence in pregnant women is limited, there is no evidence that acyclovir causes birth defects. Acyclovir should only be used during pregnancy if there are clear indications for therapy.

If I am taking any medication, what should I know?

This report provides a summary of available information about the use of PPIs during pregnancy and breastfeeding. Content is from the product label unless otherwise indicated.

You may find Pregistry's expert reports about infections here and reports about the individual medications used to treat infections here.   Additional information can also be found in the resources below. 

For more information about acyclovir during and after pregnancy, contact http://www.womenshealth.gov/ (800-994-9662 [TDD: 888-220-5446]) or check the following link:

U.S. Food and Drug Administration: Zovirax Prescribing Information

Read the whole report
General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.