Herpes simplex virus (HSV), which causes both oral cold sores (HSV-1) and genital herpes (HSV-2), can be transmitted to an infant. Though rare, this transmission can lead to neonatal herpes, a severe and life-threatening condition requiring careful medical management throughout pregnancy and delivery. Neonatal herpes affects approximately 1 in every 3,200 live births in the United States. The risk varies significantly depending on the timing of the parent’s infection and the presence of active virus during birth. Understanding the difference between a first-time infection and a recurrent outbreak is the first step in mitigating this risk.
Understanding Transmission Risk: Primary vs. Recurrent Infection
The risk of passing the herpes virus to a newborn is highest when a person acquires a primary genital HSV infection late in the third trimester of pregnancy. When a parent has a primary infection close to delivery, their body has not had enough time to produce and pass protective antibodies to the fetus. This results in a transmission risk as high as 30% to 50% during a vaginal birth, due to the large amount of virus being shed and the lack of maternal antibodies.
In contrast, the transmission risk is significantly lower—less than 3%—for people who have a history of genital herpes and experience a recurrent outbreak at delivery. If the infection was acquired before pregnancy, maternal antibodies have been produced and transferred across the placenta, offering the baby protection. Transmission can occur in three ways: in utero (before birth, which is rare), perinatally (during passage through the birth canal, which accounts for up to 85% of cases), or postnatally (after birth).
Preventing Transmission Through Prenatal Management
Medical strategies focus on reducing the likelihood of a genital herpes outbreak and viral shedding near the time of delivery. For individuals with a history of recurrent genital herpes, healthcare providers often recommend suppressive antiviral therapy starting at or beyond 36 weeks of gestation. This involves taking an oral antiviral medication, such as acyclovir or valacyclovir, until labor begins.
The goal of this late-pregnancy suppressive therapy is to prevent a recurrent outbreak, which reduces asymptomatic viral shedding in the genital tract. This approach can reduce the rate of active lesions at delivery and decrease the need for a Cesarean section. For people who acquire a primary infection in the third trimester, antiviral treatment is started immediately and continued until delivery due to the high transmission risk.
Delivery Decisions Based on Active Lesions
The mode of delivery centers on whether active lesions or prodromal symptoms are present at the onset of labor. Prodromal symptoms, which can include vulvar pain, burning, or tingling, indicate that the virus is reactivating and shedding, even if no visible lesions have appeared yet. If either active lesions or prodromal symptoms are present, a Cesarean section (C-section) is recommended to prevent the baby from contacting the virus in the birth canal.
Delivering via C-section substantially reduces the baby’s exposure to the virus, decreasing the risk of transmission by approximately 86%. If no active lesions or symptoms are present at the time of labor, a vaginal delivery is generally considered safe, especially if the parent has been on suppressive therapy. Healthcare providers will perform a thorough visual inspection of the genital area before delivery to confirm the absence of any signs of an active infection.
Protecting the Newborn After Birth
Postnatal transmission, though less common, can occur if the newborn comes into contact with an active herpes lesion after delivery. This risk is often associated with cold sores (HSV-1) or lesions on the hands of a caregiver, not just the parent. To prevent this, hygiene practices are necessary for anyone handling the baby, including frequent and thorough hand washing.
Any active lesions, such as a cold sore, should be covered with a bandage or a disposable mask should be worn to prevent viral spread through droplets. It is also advisable to temporarily avoid kissing the baby directly on the face, mouth, or eyes while an active oral lesion is present. Breastfeeding is safe even with a history of genital herpes, but if an active lesion is present on the breast or nipple, the baby should not feed from that breast until the lesion has completely healed.
Recognizing and Treating Neonatal Herpes
Neonatal herpes requires immediate medical attention, as a newborn’s immune system is underdeveloped and unable to effectively fight the virus. Symptoms often appear within the first four weeks of life, with the presentation classified into three main categories.
The most common type is localized skin, eye, and mouth (SEM) disease, characterized by fluid-filled blisters that appear on the skin. More severe forms include central nervous system (CNS) disease, which involves the brain and spinal cord, or disseminated disease, a widespread infection affecting multiple organs like the liver and lungs.
Signs of these severe forms can be non-specific, presenting as lethargy, irritability, poor feeding, or an unstable body temperature. Immediate diagnosis and aggressive treatment with intravenous acyclovir, an antiviral medication, is necessary. The duration of intravenous treatment is typically 14 days for SEM disease and 21 days for CNS or disseminated disease, often followed by a six-month course of oral suppressive therapy.