Despite remarkable achievements in reducing vertical transmission, we do not fully understand how it happens. What we do understand, though, is that there are many factors that affect transmission.

Of these, the level of the mother’s viral load is the most important.

Vertical transmission of HIV can happen before, during or after birth. Scientists have found several possible reasons for infection. Besides the mother’s viral load, her low CD4 count and whether she has other infections can make it more likely.

The exposure of the baby to a mother’s infected blood or other body fluids during pregnancy and delivery, as well as breastfeeding, are thought to be how transmission happens. Most transmissions happen during delivery when the baby is being born. More rarely, some transmissions happen during pregnancy before delivery. This is called in utero transmission.

This section has lots of medical words. We have explained on the first page of this section.

1 March 2013