Herpes Simplex Virus (HSV), types 1 and 2, is a common viral infection causing oral or genital sores. During pregnancy, concerns arise about the virus potentially affecting the developing baby. Routine, universal screening for HSV in all asymptomatic pregnant individuals is generally not standard practice in prenatal care. Screening is typically targeted and performed only when specific risk factors or symptoms are present, focusing attention where the risk of transmission is highest.
Understanding Prenatal Screening Protocols
Prenatal care does not usually include a default blood test for HSV because routine screening has not been shown to improve outcomes for the newborn. Healthcare providers rely on a risk-based approach, discussing any personal history of herpes or a partner’s diagnosis during initial appointments. Testing is strongly recommended when a pregnant individual shows active symptoms, such as painful genital lesions or a new outbreak.
If an active lesion is present, diagnosis involves collecting a swab sample for a viral culture or a Nucleic Acid Amplification Test (NAAT). These tests directly detect the virus and determine whether it is HSV-1 or HSV-2, which is valuable for planning care. NAAT is often preferred due to its higher sensitivity, making it more likely to detect the virus than culture, especially as lesions begin to heal.
When no active sores are present but past exposure is a concern, a blood test (type-specific serology) detects antibodies to the virus. This test looks for immunoglobulin G (IgG) antibodies, which indicate a past infection with either HSV-1 or HSV-2. The presence of these antibodies signifies that the immune system has previously encountered the virus.
Serological testing is helpful for a pregnant person whose partner has a known infection but who has no personal history of the virus. Identifying this situation allows providers to counsel the individual on prevention and monitor for a new infection. However, antibody tests only confirm past exposure and cannot determine the exact timing or location of the infection.
Risks of Transmission During Pregnancy and Delivery
The timing of when a pregnant person acquires the infection significantly influences the risk of transmission to the baby. Neonatal herpes is a serious, though rare, condition that can lead to illness or long-term disability in an infant. The highest probability of transmission (25% to 60%) occurs when a person contracts a primary genital infection late in the third trimester.
During a primary infection, the body has not had time to develop protective antibodies that cross the placenta and shield the fetus. This lack of maternal antibodies means the baby is exposed to high levels of the virus without immune protection. In contrast, the risk of transmission during a recurrent herpes outbreak is low, generally less than 3%.
The low risk with recurrence is because the immune system has already produced antibodies that are passed to the fetus, offering protection. Most neonatal infections (over 85% of cases) happen during delivery when the baby passes through the birth canal containing the virus. The infection can manifest as localized disease affecting the skin, eyes, or mouth, or as more severe forms involving the central nervous system or multiple organs.
Medical Management and Delivery Planning
Once a pregnant individual has a history of genital herpes, proactive steps are taken to minimize transmission risk. The main strategy involves suppressive antiviral therapy, typically using medications such as acyclovir or valacyclovir. These oral medications are considered safe for use during pregnancy and are often initiated around 36 weeks of gestation.
The purpose of this late-pregnancy suppressive therapy is to reduce the frequency of viral shedding and lower the chance of a recurrent outbreak near delivery. By suppressing the virus, the likelihood of active lesions or asymptomatic shedding in the genital tract at labor is diminished. This medical intervention is a factor in safely planning the delivery method.
The decision regarding the mode of delivery is based on the presence of active lesions or symptoms at the onset of labor. If an individual has active genital lesions, or prodromal symptoms like vulvar pain or tingling, a Cesarean section (C-section) is recommended. Performing a C-section prevents the baby from contacting the virus in the birth canal, significantly reducing transmission risk.
If a person has a history of recurrent herpes but has no active lesions or symptoms when labor begins, a vaginal delivery is considered safe. Furthermore, a C-section is advised for a person who acquires a primary genital infection late in the third trimester. This is recommended even if no active lesions are present, due to the high risk of viral shedding and the lack of protective antibodies.