For the first time (to my knowledge -- and I have done some, albeit limited, research) federal law is about to define "woman":
According to the Unborn Child Pain Awareness Act of 2005 (Senate Bill 51 and House Bill 356, if you're curious), it's the ova and the uterus and nothing else. The Act, which has been criticized for its possible effects on abortion law, has been referred to committee in both the House and the Senate. It contains this excellent definition:
WOMAN- The term `woman' means a female human being who is capable of becoming pregnant, whether or not she has reached the age of majority.
This definition of 'woman' was considered appropriate by both House and Senate.
As I like to say, in this culture (hell, pretty much any culture), “women” are uteruses first and people second.
This reminds me of my Queer Theory class last semester, reading Judith Butler and the like, and the difficulty we had in defining “female” at all; discussing the idea that sex may be as constructed as gender. Is a female a person with XX chromosomes? Then what about women like Jamie Lee Curtis, who has XXY chromosomes? Defining it by reproduction doesn’t work either, as you pointed out (two of my aunts were unable to concieve and adopted children; by the legislation’s definition, they are mothers, but not women). If genitalia are to be the definition, then we’re stuck with the fact of thousands of perfectly healthy intersexed babies born every year with “atypical” genitalia, as well as transexual people. Secondary characteristics don’t always hold true either; think of Frida Kahlo’s moustache (and what about females who get mastectomies and hysterectomies? are they no longer women?)
We decided that in this society we’re taught the circular reasoning that “Women” are simply “not men,” and “men” are “not women.”
So, Mom, in case you're curious, the federal government no longer thinks you're a woman.