In the absence of any medical intervention, one in three infants born to HIV-infected mothers become infected during the last months of pregnancy, during labor, or through breastfeeding. In 1994, the clinical trial ACTG 076/ANRS 24 performed in the United States and in France demonstrated that zidovudine (ZDV), an antiretroviral drug also known as AZT, combined with formula feeding, could prevent mother-to-child transmission of HIV in 70% of the cases. Yet, due to the complexity and cost of the regimen, widespread use was not possible in countries with limited resources.
In order to find an easier treatment to implement, the PHPT group conducted a study (PHPT-1) in Thailand of 1,437 women to determine if a shortened and simplified zidovudine prophylaxis would be as effective.
The study showed that the risk of transmission was reduced to 6% if the mother started treatment with zidovudine at the beginning of the third trimester of pregnancy (28 weeks’ gestation). Based on the results of this study, the Thai MOPH recommends that women start zidovudine prophylaxis at 28 weeks gestation in its national prevention program.