Pregnant women are more susceptible to the effects of microbial products (i.e., endotoxins) and were the most vulnerable subjects during the 1918 pandemic (influenza A subtype H1N1), with a mortality rate that ranged between 50 and 75% (1). Exposure to the virus during pregnancy may also have overt or subclinical effects that become apparent only over time.
Although substantial progress has been made in the understand- ing of the immunology of pregnancy, many unanswered questions remain, especially those associated with the susceptibility and sever- ity of infectious agents of mothers and unborn children (2), (3).
Epidemiological studies have demonstrated an association between viral infections and preterm labor (4, 5) and fetal con- genital anomalies of the CNS and the cardiovascular system (6–8). Although some viral infections during pregnancy may be asymptomatic (9), approximately one-half of all preterm delive-