FTR, there is also this article, which seems to be open-access:

http://www.ams.org/notices/200810/fea-gallian.pdf

"In summary, some Eastern European and Asian
countries frequently produce girls with profound
ability in mathematical problem solving; most
other countries, including the USA, do not. Children,
including girls, of immigrants to the USA
and Canada from some of the countries that excel
in the IMO are overrepresented among students
identified as profoundly gifted in mathematics;
USA-born girls from all other ethnic/racial backgrounds,
including white, are very highly underrepresented.
There exist many girls with profound
intrinsic aptitude for mathematics; however, they
are rarely identified due to socio-cultural, educational,
or other environmental factors."