Mother-to-child HIV transmission is the major source of HIV infection in children. Without any type of intervention, mother-to-child transmission rates range from 15 percent to 30 percent (without breastfeeding), and can reach 30% to 45% if a woman breastfeeds for a long time. Studies have shown that mother-to-child transmission can occur:

• During pregnancy and delivery. But, many researchers believe that most of the transmission during this time occurs in late pregnancy and during the birth process.
• From a mother to her breastfeeding child.

Much of the NICHD's research efforts in HIV/AIDS focus on developing ways to prevent HIV transmission, both through medical interventions with pregnant women, and by helping women avoid pregnancy. Through its research, the NICHD has helped make great progress in reducing the spread of HIV in these situations. In the United States, these rates dropped from 25 percent to under 2 percent as a result of discoveries made by NICHD researchers and their colleagues in medical and academic communities, and through the work of other NIH Institutes.

Research conducted by NICHD researchers found that the risk of mother-to-child HIV transmission is higher in pregnant HIV-infected women who had: high amounts of the HIV virus in their blood, low levels of a specific type of immune cell (the CD4 lymphocyte, which is the target for HIV infection), or advanced HIV disease. This research suggested that treating infected pregnant women with antiretroviral drugs that could lower viral levels, improve immune status, and reduce progression of HIV disease, might also reduce mother-to-child HIV transmission