Actually, this has been done. It was a poster presented at BBTS ASM some years ago now at, I think, but don't quote me on this, Bournemouth. I can't remember who were the authors, although one of them was certainly Dr Fiona Regan, and it won a prize (sorry to be so woolly about the details, but I am working from home today, and so don't have access to all my books, reprints, etc). Anyway, the bottom line was that the equation used for the Kleihauer test result relies on the woman being a Standard British Issue in terms of weight, height, etc, and, of course, all women average out under a bell-shaped curve (meaning some will fall outside the Standard British Issue woman, but still be within the "normal range", and some humans (including me) will fall well outside the average (in my case, not because I am exceptionally tall or short, or because I am under weight - which leaves one alternative!!!!!!!!!!!!!!!).