Nearly half of the estimated 32 million adults living with HIV worldwide are women of childbearing age. Mother-to-child transmission (MTCT) during pregnancy, delivery and breastfeeding is the primary source of HIV infection among young children. 1600 new infections occur each day, mostly in developing countries. What is the best way to reduce MTCT in regions such as sub-Saharan Africa, where breastfeeding is central to infant health?