In addition to biological plausibility, there is epidemiological evidence of an association between maternal infection and preterm birth [5] . The association is strongest for intrauterine viral infections and systemic and intrauterine bacterial infections [5, 6] . Viral infection outside the reproductive tract, including influenza infection, may also play a role in the etiology of prematurity. For example, in an analysis of 1957-1958 data, newborns of women who had serological evidence of ''Asian'' (pandemic) influenza during pregnancy were 50% more likely to be premature compared to newborns of uninfected women [2] . Moreover, a recent literature review found that SARS infection in the second or third trimester of pregnancy may be associated with spontaneous preterm delivery and early cesarean sections for deteriorating medical condition, although only 16 such cases were identified in the literature [23] . Moreover, in studies in China and Hungary, birth defects were associated with history of influenza [24, 25] .