Herpes Simplex Virus (HSV), including HSV-1 and HSV-2, is a highly prevalent infection worldwide. The concern during pregnancy is that the virus can be transmitted to the newborn, resulting in the serious condition called neonatal herpes. Although statistically rare, its potential for severe outcomes makes understanding the risks and preventive measures an important aspect of prenatal care. Transmission primarily occurs when the infant is exposed to the virus shed from the mother’s genital tract during delivery. Medical management focuses on identifying high-risk mothers and implementing interventions to protect the baby.
Risk Levels Based on Timing of Maternal Infection
The risk to the newborn depends heavily on when the mother first acquired the genital HSV infection. A primary infection acquired late in the third trimester poses the greatest danger. Since the mother has not had time to produce and transfer protective IgG antibodies across the placenta, the baby lacks passive immunity. In this scenario, the risk of transmission can be as high as 30 to 60 percent.
In contrast, a recurrent infection carries a much lower risk of transmission, typically less than 2 to 3 percent. This reduced risk is attributed to the mother’s established immunity, as maternal IgG antibodies cross the placenta and provide the baby with passive protection.
Most neonatal herpes cases (about 85 percent) are acquired during passage through the birth canal. The mother’s antibody status—her pre-existing immunity—is the most significant factor determining the risk level. Highest-risk cases often involve mothers who are unaware they have the infection, as viral shedding can occur without active lesions or symptoms.
Understanding Neonatal Herpes and Its Consequences
If the virus is transmitted to the newborn, the resulting infection, known as neonatal herpes, can have devastating consequences because an infant’s developing immune system struggles to contain the virus. Neonatal herpes is classified into three main categories based on the extent of the infection in the body. The least severe form is Skin, Eye, and Mouth (SEM) disease, which accounts for approximately 45 percent of cases. This localized infection typically presents with fluid-filled blisters on the skin, but without treatment, it can progress to more serious forms of the disease.
The other two forms, Central Nervous System (CNS) disease and disseminated disease, are significantly more serious. CNS disease involves the brain and spinal cord, making up about 30 percent of cases, and can lead to severe neurological damage, developmental delays, and seizures. Disseminated disease, accounting for roughly 25 percent of cases, is the most perilous, as the virus spreads to multiple internal organs, including the liver, lungs, and adrenal glands.
Early and appropriate treatment with intravenous antiviral medication, such as acyclovir, has significantly improved outcomes, but survivors of CNS and disseminated disease may still experience long-term neurological disability. For this reason, a high index of suspicion and immediate treatment are required whenever neonatal herpes is suspected.
Medical Strategies for Preventing Transmission
Current medical strategies focus on preventing the infant from coming into contact with the virus during the labor and delivery process. For pregnant women with a history of recurrent genital herpes, suppressive antiviral therapy is a standard intervention beginning late in the third trimester, typically around 36 weeks of gestation. Medications like acyclovir or valacyclovir are administered daily to reduce the frequency of recurrent outbreaks and, more importantly, to minimize the asymptomatic shedding of the virus at term.
This suppressive therapy has been shown to reduce the risk of active lesions at delivery, which consequently lowers the need for a Cesarean section (C-section). The primary intervention to prevent transmission is a C-section if any active genital herpes lesions or prodromal symptoms, such as vulvar pain or burning, are present when labor begins or the membranes rupture. This surgical delivery method bypasses the infected birth canal, significantly reducing the baby’s exposure to the virus.
A C-section is recommended regardless of whether the infection is primary or recurrent if active lesions are present. If a mother has a history of genital herpes but has no active lesions or symptoms at the time of labor, a vaginal delivery is generally considered safe. These proactive measures, including late-term suppressive therapy and careful monitoring for active lesions at delivery, are fundamental to minimizing the risk of neonatal herpes.