How Does HIV Pass from Mother to Child?

When a mother living with HIV becomes pregnant, one of her most pressing concerns is protecting her baby from the virus. Understanding how HIV can pass from mother to child is crucial for preventing transmission and ensuring the baby is born healthy. Without medical intervention, the risk of transmission ranges from 15% to 45% during pregnancy, delivery, and breastfeeding. However, with proper medical care and informed choices, this risk can be reduced to less than 1%.

Understanding transmission during pregnancy 🔗

HIV can cross the placenta and infect the developing baby while still in the womb. This in utero transmission accounts for a significant portion of mother-to-child infections, particularly during the later stages of pregnancy.

Research shows that transmission risk increases as pregnancy progresses, with approximately 3% occurring before 14 weeks, rising to 14% between 28-36 weeks, and 50% from 36 weeks until labor begins. The virus present in the mother’s bloodstream can pass through the placental barrier, especially when the mother has high viral loads or advanced HIV disease.

The mother’s viral load-the amount of HIV in her blood-plays a critical role in determining transmission risk. Studies have found that mothers with viral loads of 50,000 copies/mL or higher at delivery face a four-fold increase in early transmission risk. Other factors that increase risk include low CD4+ cell counts, the presence of sexually transmitted infections, and conditions like chorioamnionitis.

The high-risk period of childbirth 🔗

Delivery represents one of the most critical moments for potential HIV transmission. During birth, the baby comes into direct contact with the mother’s blood and other bodily fluids in the birth canal, creating significant exposure opportunities.

Why delivery is so risky 🔗

Mother-to-child transmission during delivery occurs when the virus passes to the baby during labor through exposure to HIV-rich maternal blood and vaginal secretions. The baby’s skin and mucous membranes may have micro-tears or areas of vulnerability that allow the virus to enter.

Several obstetric factors can increase transmission risk during delivery. Prolonged rupture of membranes, episiotomy, perineal lacerations, and intrapartum hemorrhage all increase the baby’s exposure to maternal blood. The mode of delivery also matters-vaginal delivery typically carries higher risk than cesarean section when the mother is not virally suppressed.

The timing of transmission during this period is particularly important to understand. Approximately 30% of total vertical transmission occurs during the labor and delivery process itself. This makes the hours surrounding birth a critical window for preventive interventions.

Breastfeeding and ongoing transmission risk 🔗

After birth, breastfeeding introduces another route of potential HIV transmission. The virus is present in breast milk and can be transmitted to the infant during feeding.

Understanding breastfeeding transmission rates 🔗

When mothers are infected before pregnancy, the additional risk of transmission through breastfeeding is approximately 14%. This risk accumulates over time-the longer a baby breastfeeds, the greater the cumulative exposure to HIV in breast milk.

Research indicates that breastfeeding transmission rates are at least 16%, and prolonged breastfeeding can nearly double the overall infant HIV infection rate. The risk varies depending on several factors, including the mother’s viral load in both blood and breast milk, the duration of breastfeeding, and whether feeding is exclusive or mixed with formula.

Factors affecting breastfeeding transmission 🔗

Several factors influence whether HIV passes through breast milk. The mother’s viral load in breast milk correlates with plasma viral load but isn’t always identical. Even mothers with undetectable viral loads in blood can occasionally transmit HIV through breastfeeding due to viral reservoirs in breast tissue.

Mixed feeding-combining breast milk with formula or other foods-poses higher risk than exclusive breastfeeding. The introduction of other foods can damage the infant’s gut lining, creating entry points for the virus. Maternal breast health also matters significantly, as mastitis, cracked nipples, or breast infections increase viral shedding into milk.

The timing of transmission during breastfeeding isn’t uniform. Risk appears elevated during the early postnatal period, though transmission can occur at any point during lactation. This cumulative risk means that with each passing month of breastfeeding, the total probability of transmission increases.

Prevention strategies that work 🔗

Medical advances have transformed mother-to-child HIV transmission from a near certainty to a largely preventable outcome. The key lies in addressing each transmission stage with targeted interventions.

Antiretroviral therapy during pregnancy 🔗

The cornerstone of prevention is antiretroviral therapy (ART) for the mother. When mothers receive ART throughout pregnancy and maintain viral suppression, transmission rates drop dramatically. Starting treatment as early as possible-ideally from 14 weeks of gestation or as soon as pregnancy is confirmed-provides the greatest protection.

ART works by reducing the amount of virus in the mother’s blood to undetectable levels, which means less virus is available to cross the placenta or expose the baby during delivery. Since the program began, more than 5.5 million babies have been born HIV-free to mothers living with HIV through comprehensive prevention services.

Delivery management 🔗

How and when delivery occurs can significantly impact transmission risk. For mothers who haven’t achieved viral suppression by late pregnancy, planned cesarean section at 38 weeks may reduce transmission risk compared to vaginal delivery. However, for mothers with sustained undetectable viral loads, vaginal delivery is considered safe.

Infant prophylaxis-giving antiretroviral medications to the newborn immediately after birth-provides an additional safety layer. These medications are typically continued for 4-6 weeks, offering protection during the critical early period when the infant’s immune system is most vulnerable.

Infant feeding decisions 🔗

Feeding choices after birth require careful consideration of both HIV transmission risk and the substantial health benefits of breastfeeding. For mothers on ART with sustained undetectable viral loads, the risk of transmission through breastfeeding is less than 1%, but not zero.

In settings where safe formula feeding is available and affordable, formula eliminates postnatal transmission risk entirely. However, in many parts of the world, breastfeeding provides critical protection against diarrhea, pneumonia, and malnutrition-conditions that kill far more infants than HIV.

WHO guidelines recommend exclusive breastfeeding for the first 6 months when mothers are on ART, followed by introduction of complementary foods while continuing breastfeeding through the first year. Maternal adherence to ART during breastfeeding is essential, as viral rebound increases transmission risk.

The power of comprehensive care 🔗

No single intervention works alone. The most successful prevention programs combine early HIV testing in pregnancy, immediate ART initiation, careful monitoring of viral suppression, appropriate delivery planning, infant prophylaxis, and supported infant feeding decisions with continued follow-up.

Between 2000 and 2024, approximately 4.4 million children were prevented from acquiring HIV through mother-to-child transmission as a result of these comprehensive prevention programs. This success demonstrates that with proper medical care and adherence to treatment, mothers living with HIV can have healthy, HIV-negative babies.

Regular viral load monitoring throughout pregnancy and breastfeeding ensures treatment remains effective. Support services help mothers maintain medication adherence, navigate infant feeding choices, and access the care needed for both mother and baby to thrive.

What do you think? How can healthcare systems better support pregnant women living with HIV in making informed decisions about their treatment and infant feeding options? What barriers might prevent women from accessing these life-saving prevention services?

References

1. https://www.who.int/teams/global-hiv-hepatitis-and-stis-programmes/hiv/prevention/mother-to-child-transmission-of-hiv
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3217724/
3. https://www.cdc.gov/global-hiv-tb/php/our-approach/briefbook-pmtct.html
4. https://www.sciencedirect.com/science/article/abs/pii/014067369292115V
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC3382106/
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC9114103/
7. https://www.cdc.gov/breastfeeding-special-circumstances/hcp/illnesses-conditions/hiv.html
8. https://data.unicef.org/topic/hivaids/emtct/