Safety of agents used to prevent mother-to-child transmission of HIV: is there any cause for concern?

Antiretroviral drugs have been used routinely to reduce the risk of mother-to-child transmission of HIV infection since 1994, following the AIDS Clinical Trials Group 076 trial, which demonstrated the efficacy of zidovudine in reducing the risk of in utero and intrapartum transmission. The use of antiretroviral drugs in pregnancy varies geographically, with widespread use of highly active antiretroviral therapy (HAART) in resource-rich settings for delaying maternal HIV disease progression as well as the prevention of mother-to-child transmission; however, in low- and middle-income settings, abbreviated prophylactic regimens focus on the perinatal period, with very limited access to HAART to date. The potential risks associated with antiretroviral exposure for pregnant women, fetuses and infants depend on the duration of this exposure as well as the number and type of drugs. As the benefits of HAART regimens in reducing the risk of mother-to-child transmission and in delaying disease progression are so great, their widespread use has been accepted, despite the relative lack of safety data from human pregnancies. Animal studies have suggested an increased risk of malformations associated with exposure to specific antiretroviral drugs, although evidence to support this from human studies is limited. Trials, cohorts and surveillance studies have shown no evidence of an increased risk of congenital malformations associated with in utero exposure to zidovudine, or other commonly used antiretroviral drugs, with an estimated 2-3% prevalence of birth defects (i.e. similar to that seen in the general population). Exposure to prophylactic zidovudine for prevention of mother-to-child transmission is associated with a usually mild and reversible, but rarely severe, anaemia in infants. However, a medium-term impact on haematological parameters of antiretroviral-exposed infants has been reported, with small but persistent reductions in levels of neutrophils, platelets and lymphocytes in children up to 8 years of age; the clinical significance of this remains uncertain. To date, there is no evidence to suggest that exposure to antiretroviral drugs in utero or neonatally is associated with an increased risk of childhood cancer, but the potential for mutagenic and carcinogenic effects at older ages cannot be excluded. Nucleoside analogue-related mitochondrial toxicity is well recognised from studies in non-pregnant individuals, whilst animal studies have provided evidence of mitochondrial toxicity resulting from in utero antiretroviral exposure. Clinically evident mitochondrial disease in children with antiretroviral exposure has only been described in Europe, with an estimated 18-month incidence of 'established' mitochondrial dysfunction of 0.26% among exposed children. Regarding pregnancy-related adverse effects, increased risks of prematurity, pre-eclampsia and gestational diabetes mellitus have been reported by a variety of observational studies with varying strengths of evidence and with conflicting results. Based on current knowledge, the immense benefits of antiretroviral prophylaxis in prevention of mother-to-child transmission far outweigh the potential for adverse effects. However, these potential adverse effects require further and longer term monitoring because they are likely to be rare and to occur later in childhood.