The virus that causes AIDS, HIV, can be transmitted from an infected mother to her newborn child. Mothers with higher viral loads are more likely to infect their babies.
Infection can occur any time during pregnancy, but usually happens just before or during delivery.
The baby is more likely to be infected if the delivery takes a long time. During delivery, the newborn is exposed to the mother's blood. Drinking breast milk from an infected woman can also infect babies. Transmission rates are lowest if the mother takes AZT during the last six months of her pregnancy, and the newborn takes AZT for six weeks after birth. Even if the mother does not take antiviral medications until she is in labor, the transmission rate can be cut by almost half.