Transmission of HIV infection from mother to child (vertical transmission) occurs in 20-30% of cases with HIV-infected mothers, in the absence of any intervention. Mostly transmission occurs either at the time of the vaginal delivery, or through breast-feeding. Other factors affecting transmission include maternal viral load and CD4 count. There are several interventions which can reduce the risk of transmission, including use of antiretroviral therapy, elective delivery by Caesarean section and appropriate use of non-breast milk. Many pregnant women may not know their HIV status; therefore, counselling and testing should be a part of all pre-natal care. In some parts of the developing world, women are being offered short-course zodovudine treatment or a single dose of nevirapine during labour with a further dose given to the baby after birth. This is a cheap and effective regime; however, there are fears that it could compromise the mother's future use of antiretroviral therapy because of development of resistance. In Europe, women are more likely to have long-term antiretroviral therapy or use monotherapy throughout pregnancy to lower viral load and delivery by elective Caesarean section, which will cut the risk of transmission to less than 2%.