One of the most intricate and hard to handle thing in french are pronouns... and here is a big one.
Simply I would say that the first "de" stands in a general case Women in general (so no specic pronoun like "les")
while in the second part "des" (de+les combined) goes with the fact that you are talking of the 57% you just talked about. which is not a general case but concerns given women.
hope that helps
and I am sure that some grammar specialists around will give a much clearer explanation than me
