The use of maternal ART has led to perinatal transmission rates of less than 2 percent, compared to rates as high as 36 percent in the absence of ART.^87,88 The literature regarding choice of ART during pregnancy, labor, and delivery continues to evolve rapidly. The landmark ACTG 076 study used a three-part AZT monotherapy regimen—antepartum and intrapartum for the mother, postpartum for the newborn—and reduced MTCT rates from 26 percent to 8 percent. ⁸⁹ Since that trial, a number of other studies have attempted to determine whether shorter courses of monotherapy for the mother and/or infant, or combinations of ART, have equal or greater efficacy.⁹⁰ Efficacy has been shown for regimens involving AZT alone, AZT and lamivudine (3TC), NVP alone (single-dose to mother and infant), AZT with single-dose NVP, and AZT and 3TC with single-dose NVP.^91–101 In wealthy countries, the current standard of care for pMTCT is triple-drug maternal ART.¹⁰² In a multivariate analysis, adjusting for maternal viral load and duration of therapy, the odds-ratio of MTCT for women receiving potent triple therapy compared with AZT mono-therapy was 0.27, supporting the benefit of using three drugs. ¹⁰³ Furthermore, data from PACTG 367 demonstrated that the use of two or more drugs is superior to monotherapy.¹⁰⁴

In addition to lowering the risk of MTCT, combination therapy also diminishes the risk of developed drug resistance in the mother. After the use of single-dose NVP for pMTCT, strains of HIV resistant to NNRTIs have been found (at least temporarily) in just under 50 percent of babies and a little more than 50 percent of women.^105–107 The clinical significance of this finding with regards to future pregnancies and future management of maternal and pediatric disease is currently unknown.