How and why does vertical transmission happen?

Despite huge reductions in vertical transmission, we do not fully understand exactly how transmission happens. But, we do understand that there are many factors that affect 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 the mothers blood or other body fluids during pregnancy, delivery and breastfeeding.

Most transmissions happen during delivery.

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

This section has lots of medical words. We have explained these here.

Last updated: 1 December 2015.