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Mother-to-child transmission (MTCT) is the overwhelming source of HIV infection in young children. Without preventive intervention, the probability that an HIV-positive woman's baby will become infected ranges from 15 to 25 per cent in industrialized countries and 25 to 35 per cent in developing countries.

The virus may be transmitted during pregnancy, labour, delivery, or after the child's birth during breastfeeding. Where breastfeeding is the norm, it may account for more than one-third of all transmissions. Since the beginning of the pandemic, about 90 per cent of all HIV-positive infants have been born in Africa. However, cases in India and Southeast Asia appear to be rising rapidly.

In 1994 a regimen using the antiretroviral drug zidovudine (ZDV, also called AZT) was shown to reduce MTCT by about two-thirds in the absence of breastfeeding. This ACTG 076 regimen is now widely used in industrialized countries, but, at an average cost of US$ 1,000 per pregnancy, it is too expensive for widespread use in poor countries. In a trial concluded in Thailand in February 1998, a short regimen of zidovudine pills in the last weeks of pregnancy cut the rate of MTCT during childbirth by half, at less than a tenth of the cost of ACTG 076. Because the women were also given safe alternatives to breast milk, MTCT in the study population was reduced to 9 per cent. Testing of newer, less costly regimens is ongoing (see below).

Any national strategy to prevent mother-to-child transmission should be part of broader strategies to prevent the transmission of HIV and STDs, to care for HIV-positive women and their families, and to promote maternal and child health. The ability to quickly make interventions to reduce MTCT widely available depends on political will, affordability of the interventions, and the strength of existing human resources and infrastructures. Powerful means of effecting change lie in demonstrating the success of interventions to reduce mother-to-child transmission of HIV, as well as the costs of not acting to prevent this kind of transmission.

Essential infrastructure and support services

Four factors that affect the affordability of interventions to prevent mother-to-child transmission are: the cost of drugs; the cost of safe alternatives to breastfeeding; the cost of HIV tests; and the cost of service delivery. WHO has added ZDV for mother-to-child transmission to the Essential Drug List. Glaxo-Wellcome has recently offered ZDV at substantially reduced prices. Further negotiations are planned to minimize the cost of the first three of these factors.

The following parameters describe the optimum context in which to implement effectively the interventions necessary to reduce transmission of HIV from mother to child:

· All women should have knowledge about HIV and access to the information necessary to make appropriate choices about HIV prevention and about sexual and reproductive health and infant feeding in the context of HIV.

· HIV counselling should be available for pregnant women and those contemplating pregnancy. Such counselling should address reproductive health issues such as family planning and safe infant feeding. Active referral and/or networking for follow-up counselling, comprehensive care, and social support should be available for HIV-positive women and their families.

· Pregnant women, and those contemplating pregnancy, should have access to voluntary HIV testing, to test results with the least possible delay (requiring that appropriate laboratory services be available to process such tests), and to counselling.

· All pregnant women should have access to antenatal, delivery, and postpartum care, and to a skilled attendant at birth.

· There should be follow-up of children at least until 18 months, especially for nutrition and for childhood illnesses.

Recent trials of antiretroviral regimens against MTCT

In 1999, three existing randomized controlled trials of short-course zidovudine monotherapy conducted in Thailand and West Africa were concluded. Although the risk of transmission of HIV from mother to child was greater in the breastfeeding populations, the relative decrease in transmission risk was similar for all three trials, between 40 and 50 per cent.

Concurrently, another study, the PETRA trial, conducted a randomized controlled trial of HIV-positive pregnant women from three countries in Africa. There were four arms to the trial, three using various regimens of ZDV and 3TC (lamivudine), the fourth using a placebo. Arm A of the trial included antenatal, intrapartum, and postpartum treatment; arm B intrapartum and postpartum treatment; arm C intrapartum alone; and arm D the placebo. In September 1999, the risk of transmission in each group was: Arm A 8.6%; Arm B 10.8%; Arm C 17.7%; Arm D 17.2%.

In July 1999, a joint Uganda-US study compared the efficacy of a single dose of the antiretroviral drug nevirapine with a short regimen of ZDV given in labour to the mother and administered to the baby for one week after delivery. HIV infection was reduced from 25 to 13 per cent in infants about three months of age (see HIVNET 012 study in this section).