This might interest you.Click on the map to see the full size version. The key reads that Navy Blue countries have over 3 times as many female relatives of American citizens being brought into America as males. Medium Blue countries are 2x. At the other end of the scale is Dark Red.
I collected data from the new DHS site's immigration statistics division for the years 2003-2006 on the gender of immigrants who were admitted as 'immediate relatives of U.S. citizens'. As a practical matter, the majority of such immigrants are the SPOUSES of U.S. citizens (who may or may not be native-born Americans). Although DHS very unhelpfully stopped collecting separate statistics for spouses, parents, and children in 2003, I did my best to cut out adopted orphans which would skew the ratio for some important countries such as Russia, China, and Korea, which I did for 2003, 2005, and 2006 (2005 had defective data which included only about half of adopted orphans).
The upshot of all this is that doing this seems to show nicely how attractive the men versus the women of a given nation are!
I haven't looked into this in detail, but it looks pretty plausible. I suppose it could be skewed by arranged marriages, such as all the arranged cousin marriage that bring Pakistani boys to Britain to marry their cousins. Another thing that could skew it is citizens bringing in non-spouse relatives, such as widowed moms and sisters. This would be especially high for countries that mostly send men to America as pioneering immigrants.
And it would be interesting to look at the sex ratio of foreign adoptions, since prospective American parents are very interested in how well their future child will do in the American marriage market.
But, it's a good start.