Human Immunodeficiency Virus (HIV) impacts millions worldwide. A key concern is the transmission of HIV from a mother to her child, known as vertical transmission. Understanding this mode is vital for public health, as it is the primary way children acquire HIV, highlighting the need for preventative measures.
Defining Vertical Transmission
Vertical transmission of HIV is the passage of the virus from a mother living with HIV to her child. This can occur during pregnancy, childbirth, or through breastfeeding. Without medical interventions, the risk of a child acquiring HIV ranges from 15% to 45%. Historically, vertical transmission accounted for about 90% of HIV cases in children. Medical advances have since significantly reduced these rates.
Pathways of Transmission
The virus can be transmitted during pregnancy when it crosses the placenta, potentially entering the fetal bloodstream. Factors such as placental infections, recent maternal HIV infection, or advanced maternal HIV disease can compromise the placental barrier, increasing this risk. Some infants are born with detectable HIV in their blood, confirming in utero transmission.
During labor and delivery, the baby is exposed to the mother’s blood and other bodily fluids. Contact with cervical secretions or blood poses a substantial transmission risk. Procedures like amniotomies or episiotomies, and prolonged rupture of membranes, can increase this risk.
After birth, HIV can be transmitted through breast milk. The virus is present in the milk, and the infant’s gut mucosal surfaces are a common entry point. Factors increasing transmission risk include a high maternal viral load, breast inflammation like mastitis, and prolonged or mixed feeding practices.
Strategies to Prevent Transmission
Antiretroviral therapy (ART) for pregnant mothers is a primary prevention strategy. It dramatically reduces the mother’s viral load, lowering the risk of transmission to the infant. Initiating ART early in pregnancy, ideally before conception, and maintaining adherence throughout pregnancy, childbirth, and breastfeeding significantly reduces the risk to less than 1%. These medications suppress the virus in the mother and can cross the placenta to protect the baby.
Managed labor and delivery also prevent transmission. Vaginal deliveries are generally safe for mothers on ART with undetectable viral loads. However, a Cesarean section (C-section) may be recommended if the mother’s viral load is unknown or high (over 1,000 copies/mL) near delivery. An elective C-section, performed before labor and membrane rupture, minimizes the baby’s exposure to maternal fluids.
Infant prophylaxis involves administering ART to newborns shortly after birth to prevent infection. All infants born to mothers with HIV should receive antiretroviral prophylaxis as soon as possible, ideally within six hours of delivery. The specific regimen and duration depend on the mother’s viral load and other risk factors, with high-risk infants often receiving a combination of three drugs for several weeks.
Safe infant feeding practices are also a consideration. In settings where safe water and formula are readily available, formula feeding eliminates the risk of HIV transmission through breast milk. However, in regions where access to safe formula and clean water is limited, the World Health Organization recommends exclusive breastfeeding for the first six months, alongside consistent maternal ART, as the benefits of breastfeeding can outweigh the risk of transmission.
Diagnosis and Care for Exposed Infants
After birth, prompt and accurate diagnosis is crucial for infants born to mothers with HIV. Unlike adults, antibody tests are not reliable for diagnosing HIV in infants younger than 18 months due to the presence of maternal antibodies. Instead, virologic tests that directly detect the virus, such as HIV DNA PCR or HIV RNA nucleic acid tests (NATs), are used. These tests can identify HIV infection within the first few weeks of life, with testing recommended at birth, 14 to 21 days, 1 to 2 months, and 4 to 6 months of age for exposed infants.
If an infant is diagnosed with HIV, initiating antiretroviral therapy (ART) as early as possible significantly improves outcomes. Early ART leads to faster viral suppression, improved neurodevelopmental outcomes, and a reduction in the viral reservoir in the infant’s body.
Ongoing monitoring and care are provided for exposed infants, regardless of their initial HIV status. This includes regular follow-up appointments and continued testing, especially for breastfed infants, to ensure early detection of any new infection. Prophylaxis against opportunistic infections, such as Pneumocystis jiroveci pneumonia, is also given to infants at risk until their HIV status is confirmed negative.
Global Progress in Eliminating Vertical Transmission
Significant global achievements have been made in reducing vertical HIV transmission rates over the past decades. The concept of “elimination of mother-to-child transmission” (EMTCT) has become a global public health priority, with several countries achieving or nearing this milestone. For HIV, the World Health Organization’s impact criteria for validation of EMTCT include fewer than 50 new pediatric infections per 100,000 live births and a transmission rate of less than 5% in breastfeeding populations or less than 2% in non-breastfeeding populations.
This progress is largely attributed to increased access to antiretroviral therapy for pregnant women living with HIV. In 2019, about 85% of women globally had access to ART to prevent mother-to-child transmission. Global initiatives have driven substantial reductions in new pediatric HIV infections. However, challenges persist in ensuring consistent access to testing and treatment in all regions, particularly in high-burden settings.