The placenta and viral infections.

Many viruses can infect the fetus in utero, by either ascending or hematogenous routes. Much is known about the maternal-fetal passage of virus from clinical, virologic, and serologic studies. Although transplacental passage is a key aspect of these infections, there is much more limited information about changes in the placenta. For a few infections, placental characteristics have been well described, and there is now increasing information on many others. Newer techniques for in situ demonstration of viruses will hopefully yield much information about diagnosis and the mechanisms of transplacental passage.