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Mechanisms and timing of mother‐to‐child transmission of HIV‐1

A growing body of clinical and laboratory evidence supports several possible mechanisms of vertical HIV transmission including maternal disease state and viral load fetal exposure to infected maternal body fluids during pregnancy and delivery and breast feeding. More precise knowledge of the timing of maternal-infant transmission would help identify the periods of greatest risk and suggest approaches to reduce this risk. This article reviews the research literature on intrauterine transmission intrapartum transmission breast feeding and the hypothesized timing of HIV transmission. The research evidence suggests that transmission during late pregnancy and the intrapartum period contributes relatively more to the overall rate of vertical HIV transmission than the early intrauterine period even in populations where breast feeding is the norm and that postnatal transmission through breast feeding confers a substantial additional risk of infection.