There was a study done in Germany in 1980 (Dorner, G., Geier, T.,
Ahrens, L., Krell, L., Munx, G., Sieler, H., Kittner, E., and Muller, H.,
"Prenatal stress as possible aetiogenetic factor of homosexuality in human
males" Endokrinologie 75:365-386). This study reported a greater incidence of
homosexuality among men born during the Second World War.
Another study in 1988 (Ellis, L., Ames, M.A., Peckham, W., and Burke,
D. reported in the Journal of Sex Research 25:152-157) seems to offer partial
support for the stress hypothesis.
But a study done in 1991 (Bailey, J.M., Willerman, L., and Parks, C. "A
test of the maternal stress theory of human male homosexuality." Archives of
Sexual Behavior 20:277-293) came up with a totally different conclusion. This
study reported that women who have had a gay and a straight son do not recall
different levels of stress during the two pregnancies.
I tend to believe that stress may have SOME effect - under certain
circumstances - but not that great of an effect or there would be a more easily
charted correlation between wars, earthquakes, etc., and the presence of
homosexuals in a particular society. And what should not be ignored is that a
few people might be born homosexual because of maternal stress - but the
majority of those who are born homosexual are homosexual because of a genetic
predisposition.
http://www.skepticfiles.org/gay/stress.htm