An HIV-positive woman can pass on HIV to her baby during pregnancy, or during delivery, or by breastfeeding.

Anti-HIV treatment can, however, greatly reduce the risks of a woman passing on HIV to her baby. Having a caesarean rather than a vaginal delivery can reduce the risks even further. The exclusive use of formula feed is strongly recommended for all babies with HIV-positive mothers in the UK. Using these methods, it’s possible to reduce the risk of mother-to-baby transmission of HIV from about one in four to less than one in a hundred.

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 HIV viral load is detectable.

• Having a difficult delivery, requiring, for example the use of forceps.

• Breastfeeding.