How can HIV pass from a mother to an infant at birth?

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Infographic showing estimated lives saved by childhood vaccinations worldwide from 1974 to 2024, with syringe-shaped bars for each disease. Measles tops the list at 93.71 million lives saved, followed by tetanus, whooping cough, and others, for a total of 153.84 million lives saved. — childhood disease and disorder Vaccines and the estimates of lives saved over the period 1974–2024.

Mother-to-child transmission of HIV, also known as vertical or perinatal transmission, occurs when the virus passes from an HIV-positive mother to her infant during pregnancy, labor, or delivery, or through breast-feeding.1

During birth specifically, the infant is exposed to the virus through contact with maternal blood and other bodily fluids. Without preventative measures, the risk of transmission is approximately 15 to 30 percent, though this can be reduced to less than 2 percent through the use of antiretroviral drugs by the mother before birth and at the time of delivery, as well as treatment for the newborn.1

Additionally, an elective cesarean section performed before the onset of labor or the rupture of membranes can further lower the risk of transmission during delivery, though this procedure carries its own risks of maternal complications such as hemorrhage and fever.1