How and why does vertical transmission happen?

We now know how to get vertical transmission down to almost zero. And, we know that there are several things that increase the risk.

Of these, the mother’s viral load is the most important. Vertical transmission can happen before, during or after birth. Other risks are having a low CD4 count or other infections.

Transmission is most likely to happen if the baby comes into contact with an untreated mother’s blood or other body fluids during pregnancy, child birth and breastfeeding. Most transmissions happen during birth.

Less often, transmission can happen during pregnancy before birth. This is called in utero transmission.

Last updated: 1 November 2023.