Over the past few years, several studies have identified the risk of maternal-fetal transmission of HIV by seropositive mothers. The risk is close to 30 percent. However, for reasons not yet understood, the risk appears to be higher in Africa, approaching 40 percent, and lower in Europe, approaching 16 percent. Factors influencing maternal-fetal transmission of HIV are not well defined but may include the clinical state of the mother, plasma p24 antigen positivity of the mother, viral load, prior pregnancy associated with maternal-fetal HIV transmission, absence of maternal epitope specific and/or high affinity gp120 antibodies, or prematurity.