Herpes simplex virus (HSV) is a common viral infection with two main types: HSV-1 (oral cold sores) and HSV-2 (genital herpes). Many people carry the virus, which remains dormant in nerve cells, often with no or only mild symptoms. The presence of HSV during pregnancy is a concern due to the potential risk of transmitting the infection to the baby, a condition known as neonatal herpes. Healthcare providers focus on managing the virus throughout pregnancy to minimize this risk.
Understanding Herpes During Pregnancy
The risk of the virus passing from mother to baby is influenced by the timing of the mother’s infection. The greatest risk of transmission occurs when a pregnant person acquires a primary genital HSV infection late in the third trimester. During a primary infection, the mother has not yet developed protective antibodies that can cross the placenta to shield the fetus, making the baby highly vulnerable.
A woman who had genital herpes before pregnancy has a much lower risk of transmission, typically less than one percent. Her immune system has produced antibodies that pass through the placenta, providing natural protection to the baby. Even during a recurrent outbreak near delivery, these circulating antibodies mitigate the danger to the infant.
The virus can be transmitted through three routes, though one is significantly more common. The rarest route is in utero transmission, where the virus crosses the placenta during pregnancy. Transmission can also occur via an ascending infection, where the virus travels upward from the cervix after the rupture of membranes. Most neonatal infections, however, occur during the intrapartum period when the baby is exposed to the virus while passing through the birth canal containing active lesions or asymptomatic viral shedding.
Specific Risks to the Newborn
Neonatal herpes is a serious infection because the infant’s immune system is underdeveloped and cannot effectively fight the virus. The infection is categorized into three main forms. The mildest form is skin, eyes, and mouth (SEM) disease, accounting for approximately 45% of cases. SEM typically presents with fluid-filled skin blisters, but without treatment, it can progress to more severe systemic disease.
The second category is central nervous system (CNS) disease, where the virus has spread to the brain and spinal cord, often causing herpetic encephalitis. This form carries a high risk of long-term neurological damage, with surviving infants often experiencing developmental delays or intellectual disabilities. The most severe manifestation is disseminated disease, where the virus has spread to multiple organs (liver, lungs, and adrenal glands). This systemic infection has the highest mortality rate, even with aggressive antiviral treatment.
Prompt diagnosis and immediate treatment with intravenous antiviral medication are crucial for improving outcomes. Even with treatment, survivors of CNS and disseminated disease frequently require long-term medical support due to permanent damage. Preventing transmission by identifying and treating the mother remains the primary focus of perinatal care.
Managing Maternal Herpes Infection
Management begins with accurate diagnosis, involving viral cultures or PCR testing of active lesions to confirm the virus. Serologic testing determines if the mother has antibodies to HSV-1 or HSV-2, distinguishing between a primary and a recurrent infection. These steps help healthcare providers tailor the management strategy to the specific risk level.
Antiviral medications, such as acyclovir and valacyclovir, are considered safe during pregnancy to treat active outbreaks. These drugs interfere with the virus’s ability to replicate, accelerating the healing of lesions and reducing viral shedding. For women experiencing a primary infection in the third trimester, continuous antiviral therapy may be prescribed until delivery to minimize transmission risk.
The most common preventative strategy is suppressive antiviral therapy, typically initiated at or beyond 36 weeks of gestation. This regimen involves taking a daily dose of medication, usually acyclovir or valacyclovir, until delivery. The purpose of this late-term suppression is to decrease clinical recurrences and reduce the likelihood of asymptomatic viral shedding during labor. This measure is highly effective in reducing the need for a Cesarean section.
Delivery Options and Prevention
The mode of delivery is a critical step in preventing neonatal herpes transmission, depending entirely on the mother’s status at the onset of labor. A Cesarean section is recommended if a pregnant person presents with active genital lesions or prodromal symptoms (such as tingling or vulvar pain) at the time of labor or membrane rupture. These symptoms suggest active viral replication and a high risk of the baby contacting the virus during passage through the birth canal.
For a woman with a history of recurrent herpes who has no visible lesions or symptoms at the onset of labor, a vaginal delivery is generally safe. Suppressive antiviral therapy taken since 36 weeks significantly reduces viral shedding, making the transmission risk very low. In these cases, the benefits of a vaginal birth typically outweigh the minimal risk.
Aside from medication and delivery planning, additional preventive measures are employed during labor. Invasive procedures, such as using a fetal scalp electrode for internal monitoring or an operative vaginal delivery (forceps or vacuum), are generally avoided. These procedures can create small breaks in the baby’s skin, potentially providing an entry point for the virus, and are only utilized when medically necessary.