How mother-to-baby transmission occurs

• during pregnancy – the foetus is infected by HIV in the mother's blood crossing the placenta
• during delivery – the baby is infected by HIV in the mother's cervical secretions or blood during childbirth
• during breastfeeding – the baby is infected by HIV in the mother's breast milk or blood during breastfeeding.

A number of factors can make it more likely that a woman will pass on HIV to her baby. These include:

• Being ill because of HIV
• Having a high HIV viral load and a low CD4 cell count
• Waters breaking four hours or more before delivery
• Having an untreated sexually transmitted infection at the time of delivery
• Using recreational drugs, particularly injected drugs, during pregnancy
• Having a vaginal delivery (rather than a caesarean delivery) if your HIV viral load is detectable
• Breastfeeding. 

But if you have the right treatment and care during your pregnancy, you have an undetectable viral load, and you don’t breastfeed, the chance of passing on HIV to your baby is very, very small – about one in 1,000.