Herpes simplex is a well-known virus that usually causes sores on the mouth or the genitals. Type 1 usually occurs above the waist, resulting in so-called cold sores and fever blisters. Type 2 normally causes genital blisters and sores. Oral sex can transfer the virus from a cold sore to the genital area, reducing the distinction between the two types.

The herpes virus enters the body through the skin or mucous membranes, usually by way of sexual contact. The first time you experience an episode, called primary herpes, you will usually have painful sores and a flu-like syndrome as the virus spreads throughout the body. Be alert for the following: genital itching and tingling, painful urination, and sores or blisters on the labia or inside the vagina. What's particularly unusual about the herpes virus is that it may enter some of the nerves of the body and travel toward the spine, remaining there in spite of antibodies that prevent infection elsewhere. Then, over the years, the virus travels down the nerves periodically to the skin, where it causes recurrent lesions. These blisters and sores, containing the contagious virus, last for 7 to 10 days and resolve spontaneously. Some patients have only one outbreak, and others have recurrences for years.

The herpes virus may cause problems during pregnancy in two ways. If you had herpes before you got pregnant, you will very likely have built up antibodies by now, and the odds are small that the virus will cross the placenta and infect your fetus. But if you develop your first episode of herpes during pregnancy, the virus may indeed cross the placenta and infect the fetus. If this occurs during the first three months of pregnancy, the result can be miscarriage, birth defects, or fetal death. The more common scenario is that if the virus is present in the genital tract when the membranes are ruptured or when the fetus passes through the birth canal, the infection is passed to the fetus about half the time. Although it's possible that the resulting disease will be mild, most newborns suffer severe damage or even death. A small number of women can shed the virus from the cervix or vulva without experiencing symptoms, a situation that seems to occur more often with the first infection.

If you notice you're having an outbreak with visible lesions during pregnancy, your doctor will take a culture to confirm the diagnosis. A vaginal delivery will be allowed if there are no visible lesions at the onset of labor. A culture is not necessary if you have had herpes in the past but have no symptoms prior to delivery. On the other hand, a cesarean section is recommended if there are visible lesions when labor begins, or if you have symptoms within four to six hours of when your membranes rupture or at the onset of labor.

Our best approach to herpes in pregnancy involves prevention. No medication yet exists to cure herpes, nor is there a vaccine against it. One medication, acyclovir, may suppress outbreaks for a while if you take it continuously, or it may shorten the length of time the sores last if it's used at the time of an outbreak. But acyclovir should not be used during pregnancy or when trying to conceive, as its safety in pregnancy is not established.

If you do not have herpes, during preconception you should avoid sexual exposure to anyone who has the virus. If your partner has herpes, avoid sex during an outbreak and use condoms at other times. To be most safe, you may want to abstain from sexual relations completely during the first three months and the last two months of pregnancy. Although most herpes is transmitted by direct sexual contact, there is a small possibility that it could be passed by a towel or toilet seat. If your partner has an outbreak, use separate towels and clean the toilet seat and bathtub with bleach after each use to reduce your risk of infection.