HIV medicines prevent HIV from multiplying, which reduces the amount of HIV in the body (called the viral load). An undetectable viral load is when the level of HIV in the blood is too low to be detected by a viral load test. The risk of mother-to-child transmission of HIV during pregnancy and childbirth is lowest when a woman with HIV has an undetectable viral load. Maintaining an undetectable viral load also helps keep the mother-to-be healthy.

Some HIV medicines used during pregnancy pass from the pregnant woman to her unborn baby across the placenta. This transfer of HIV medicines protects the baby from HIV, especially during a vaginal delivery when the baby passes through the birth canal and is exposed to any HIV in the mother's blood or other fluids. A scheduled cesarean delivery (sometimes called a C-section) can reduce the risk of mother-to-child transmission of HIV in women who have a high viral load (more than 1,000 copies/mL) or an unknown viral load near the time of delivery.

After birth, babies born to women with HIV receive HIV medicine to reduce the risk of mother-to-child transmission of HIV. Several factors determine what HIV medicine they receive and how long they receive the medicine.