Vertical transmission, or mother-to-child transmission, is the primary way human immunodeficiency virus (HIV) is passed to children globally. Medical advances have fundamentally altered this situation, reducing the risk of transmission to one percent or less where consistent medical care is available. This success is achieved through a coordinated, multi-stage strategy that manages the mother’s viral load and protects the infant through and after birth. The modern approach focuses on early identification and continuous treatment throughout the reproductive journey.
How and When Vertical Transmission Occurs
HIV can be transmitted from a mother to her child at three distinct points. The first is during pregnancy, known as in utero transmission, where the virus crosses the placenta to infect the fetus. This pathway is the least common, typically accounting for about 5 to 10% of transmissions without intervention.
The second and most frequent route occurs during labor and delivery, termed intrapartum transmission. As the infant moves through the birth canal, they are exposed to maternal blood and secretions containing the virus. Without treatment, this stage accounts for the highest percentage of transmissions, estimated between 10 and 20% of cases.
The final route is postnatal transmission, which happens through breastfeeding. HIV can be present in breast milk, and the risk continues for the entire duration of feeding. Without preventive treatment, the total cumulative risk of vertical transmission through all three periods can approach 40%.
Modern Prevention Through Maternal Treatment
The cornerstone of preventing vertical transmission is the mother’s use of Antiretroviral Therapy (ART). ART is a combination of medications that suppresses viral replication, dramatically reducing the amount of HIV in the mother’s blood, known as the viral load.
The primary goal is to achieve an undetectable viral load, typically defined as fewer than 50 copies per milliliter of blood. When the viral load is suppressed to this level, the risk of transmission during pregnancy and delivery is virtually eliminated. Studies show that for mothers who maintain an undetectable viral load throughout pregnancy, the transmission risk is less than 1%.
Early diagnosis of HIV and the immediate initiation of ART are essential to ensure the virus is suppressed before birth. Treatment should start as soon as possible, regardless of the mother’s CD4 cell count or the stage of pregnancy. Consistent adherence to the medication regimen is required to maintain this undetectable status.
Sustained viral suppression minimizes the amount of HIV that can cross the placenta or be present in maternal fluids during delivery. This high efficacy has transformed HIV from a high-risk factor in pregnancy to a manageable condition, making viral suppression the single most effective intervention.
Delivery Protocols and Infant Feeding Decisions
Labor and delivery logistics are managed based on the mother’s viral load near the time of birth, typically measured around 36 weeks of gestation. If the mother has achieved and maintained an undetectable viral load, a vaginal delivery is considered safe and is the recommended route.
If the viral load is high, generally defined as greater than 1,000 copies per milliliter, a scheduled Cesarean section is recommended. This surgical delivery is typically performed at 38 weeks of gestation, before the onset of labor or rupture of membranes. The C-section minimizes the infant’s exposure to maternal blood and genital tract secretions during birth.
A key decision involves infant feeding, which varies based on the resource setting. In high-resource countries where access to clean water and affordable formula is guaranteed, the recommendation is to completely avoid breastfeeding. Formula feeding eliminates the final route of potential transmission, offering a zero-risk option.
In low-resource settings, formula feeding often poses a greater risk of malnutrition or infection. Therefore, the World Health Organization recommends that mothers with HIV exclusively breastfeed while remaining on ART. Here, the benefits of breastfeeding for infant survival often outweigh the small residual risk of transmission, provided the mother is consistently taking her medication. The feeding decision requires detailed counseling and support from the healthcare team.
Post-Birth Testing and Care for Exposed Infants
Every infant born to a mother with HIV is considered exposed and receives immediate medical attention, even if the mother achieved an undetectable viral load. This involves administering prophylactic antiretroviral medication to the newborn as soon as possible, ideally within six hours of birth. This short-term post-exposure prophylaxis prevents any virus encountered during birth from establishing a permanent infection.
The specific prophylactic regimen is determined by the mother’s viral load status near delivery. If the mother maintained a low viral load, the infant typically receives a single antiretroviral drug, such as zidovudine, for four to six weeks. If the mother’s viral load was detectable or unknown, a more intensive regimen of two or three different antiretroviral drugs is given for six weeks.
Diagnostic testing for the infant does not rely on antibody tests, as maternal antibodies can persist in the baby’s blood for many months. Instead, specialized virologic tests, such as HIV DNA Polymerase Chain Reaction (PCR) assays, are used to detect the virus itself. Testing is conducted at specific intervals:
- At 14 to 21 days of life.
- Again at one to two months.
- Finally at four to six months of age.
A negative result at the four-to-six-month mark, combined with a period of no breastfeeding, confirms the infant is not infected. This structured testing and prophylactic treatment ensure that any HIV-exposed infant who acquired the virus is identified and started on a full treatment regimen immediately.