How Herpes Affects Pregnancy

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Herpes infection in pregnant women poses a risk to their babies. However, while careful prenatal care is imperative, pregnancy and childbirth are generally safe for these women and their children.

Overview

Herpes is a very common sexually transmitted disease. In fact, it is estimated that 20% to 25% of pregnant women are carriers of the herpes virus. The vast majority of them will have children without experiencing any herpes-related complications for their babies.

However, the herpes simplex virus does pose a risk to the unborn child in certain situations and can increase the likelihood of a cesarean section. Knowing more about the risks of genital and oral herpes infections during pregnancy can help mothers-to-be and their partners make informed decisions to protect themselves and their babies.

Herpes Simplex Virus Infections

The herpes simplex virus causes a variety of infections, characterized by dormant periods with no symptoms and sporadic outbreaks of red, itchy, painful blisters. Generally, there are two types of herpes: genital herpes and oral herpes (also called cold sores or fever blisters). However, herpes lesions from both types can be found anywhere on the body, including on the skin, mouth, eyes, and genitals.

Type 1 (HSV-1) infections are most often found on the mouth, while type 2 (HSV-2) infections tend to occur in the genital area.

Transmission

A person can contract herpes when broken skin or their mouth, penis, vagina, or anus come into contact with the virus. The virus can be contagious even when visible symptoms are absent and can be transmitted via saliva and viral shedding from tissue that appears healthy. According to the Centers for Disease Control and Transmission, "most people with genital herpes do not know they have it."

Once someone has been infected, there is no cure. However, most people exhibit no signs of infection. Many women may only learn they are infected during pregnancy due to an outbreak of lesions or through antibody testing. For those that experience active infections or outbreaks, symptoms are usually intermittent.

Outbreaks

Many women have been exposed to the herpes simplex virus and developed antibodies to it without ever having had a symptomatic outbreak. During pregnancy, the immune system becomes less effective, which can trigger these women to have a first outbreak. Pregnant women previously infected with herpes will have an average of 3 recurrences during pregnancy.

About 80% of women who are infected with the herpes simplex virus will have a recurrence during their pregnancy.

Multiple factors may trigger the recurrence of symptoms, including physical and emotional stress, fatigue, hormonal changes, and exposure to extreme heat or cold. The hormonal, immune, and other physical changes that occur during pregnancy, as well as the overall toll of growing a baby, are also thought to contribute to a greater frequency of active herpes infections.

The virus remains dormant between outbreaks until reactivated. The frequency and severity of infections vary, with many people being largely asymptomatic and others having more frequent, painful infections.

Active infections tend to come and go and will usually resolve in a week or so without treatment. However, there are medications, including Zovirax (acyclovir), Famvir (famciclovir), and Valtrex (valacyclovir), that can prevent and shorten outbreaks.

What is of bigger concern, however, is the potential impact of herpes on pregnancy, as in some cases, it can have severe consequences. Below, we break down the risk to your baby and what you need to do to best protect your child.

Risk of Transmission to the Baby

The overall risk is low that a mother with herpes will transmit the virus to their child via childbirth, as long as they are not experiencing an active outbreak at the time of delivery. In fact, research shows that only 1% of babies born to carries of herpes will get infected during childbirth. Additionally, genital herpes causes more risk than oral herpes.

The specific risk of transmitting the herpes simplex virus to a baby depends on several factors:

  • Exposure of the infant to herpes lesions during delivery
  • Whether the mother has antibodies to the herpes simplex virus
  • Whether the infant has time to acquire these antibodies before delivery

To illustrate how an infant's risk changes based on the above factors, consider the following example:

A person who experiences their first outbreak of genital herpes during the third trimester of pregnancy and who has not yet developed antibodies to the virus by the onset of labor has a 33% chance of transmitting the virus to their infant during vaginal birth.

On the other hand, a woman who experiences a recurrent outbreak of genital herpes has just a 3% chance of transmitting the virus to their infant. The risk is reduced in this scenario primarily because the mother already has antibodies to the herpes virus and has passed them to their unborn child.

The greatest risk for transmitting herpes to your child occurs if you experience your first outbreak right before or during childbirth. In those cases, a cesarean section is usually performed to greatly mitigate this risk.

Effect on the Infant

Transmission of the herpes simplex virus to a newborn (neonate) can have devastating effects. The extent of the herpes simplex infection can range from a rash on the skin, to impact on the eyes and mouth, to infection of the brain, or infection throughout the body.

The herpes simplex type determines the risk to the infant. A primary or recurrent HSV-1 infection during labor is more easily transmitted to the infant but the disease is generally limited to the mouth, eyes, and mucous membranes. Primary infection with HSV-2 is more likely to affect the central nervous system, causing seizures, meningitis, developmental delay, and death.

In much less common cases, the virus may be transferred to the fetus in utero. This can cause infections of the brain, liver, eyes, lungs, and other vital organs, or even death. There is some speculation that initial herpes infection during pregnancy may slightly increase the likelihood of miscarriage and pre-term delivery, but more research needs to be done to confirm or refute these theories.

Signs of HSV infection in babies include low-grade fever, rash or blisters, poor feeding, seizures, and lethargy. Symptoms can begin two to 12 days after exposure, and the illness can worsen quickly. All infants suspected of having a herpes simplex virus infection should be treated with IV acyclovir. The length of treatment and prognosis is determined by the body system involved in the infection.

Treatment of Herpes in Pregnancy

The recommendation of the American College of Obstetricians and Gynecologists (ACOG) is to treat all primary outbreaks of genital herpes with antiviral medications, including primary outbreaks in pregnant women.

Acyclovir has the most data on the safety of use in pregnancy. A registry of over 1000 pregnant women who were exposed to acyclovir during early pregnancy suggests that acyclovir is most likely safe, as there were no increases in birth defects.

Most women who have a current outbreak of genital herpes, primary or recurrent, are usually advised to have a cesarean section to reduce the exposure of the infant to the herpes simplex virus. However, women with known herpes exposure usually take an antiviral medication in the third trimester to prevent outbreaks—and are able to safely deliver vaginally.

Precautions for Pregnant Women Without Herpes

While any woman who has never had herpes should be cautious about having sex with someone who might have herpes, pregnant women should take extra precautions in their third trimester. These guidelines include avoiding intercourse and oral sex with partners who have, or you suspect have, genital herpes.

If you're uncertain if you've been exposed to herpes, consider asking your obstetrician about HSV antibody testing to be sure.

A Word From Verywell

While having herpes does pose some added risk to your baby, know that in the vast majority of cases no complications will occur—and herpes will not be passed to the baby. Assuming they are receiving appropriate medical care, most mothers who have herpes have very little to worry about and will go on to deliver healthy babies.

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  1. Kang SH, Chua-Gocheco A, Bozzo P, Einarson A. Safety of antiviral medication for the treatment of herpes during pregnancy. Can Fam Physician. 2011;57(4):427-428.

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