Our findings in the Helsinki Influenza Study and the Danish Forty Year Study lead us to
conclude that a 2nd-trimester maternal influenza infection may increase risk for adult
schizophrenia or adult major affective disorder. More recently we have also reported an increase
of unipolar depression among offspring who were exposed prenatally to a severe earthquake (7.8
on the Richter scale) in Tangshan, China. Among the earthquake-exposed males (but not the
females), we observed a significantly greater depression response for those individuals exposed
during the 2nd trimester of gestation. These findings suggest that maternal influenza infection
and severe maternal stress may operate (in different ways) as teratogens, disrupting the
development of the fetal brain and increasing risk for developing schizophrenia or depression in
adulthood.