The prevalence of human immunodeficiency virus (HIV) infection in women of the reproductive age group has been increasing and, with it, vertical transmission of the virus to their infants. It is currently believed that intrauterine transplacental infection of the fetus is the most important mechanism of vertical transmission; thus, a recent focus of investigation has been on the role of the placenta in maternofetal HIV infection. However, the mechanisms by which infectious agents cross the

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... nta to infect the fetus remain largely unknown. Some lessons of possible relevance to issues related to vertical HIV transmission may be gained by reviewing the experience with other agents that can affect the fetus and newborn. This communication examines current virologic and clinicopathologic features of perinatal HIV infection in light of concepts of placental and fetal infection with other viral agents in an attempt to find a model of vertical HIV transmission.