I think some of the deal is that STATISTICALY, women do tend to go ff and get pregnant, and that puts a crimp in any buisness. It is NOT universally true, but any employer looking at the bottom line IS going to look at the fact that women between the ages of 20 and 30 tend to get pregnant, weather they come into an interview saying 'I am going to have a family' or not.
Now one thing they often miss out on is that mothers are better (statistically) multitaskers, and such. But in the case of emergency work? that old Male gotta protect her kicks in. (statistically) plus the (statistical) trend for women to go off and get pregnant. (and btw a large number of women do NOT return after having the kid, so no multitask boost)
The cure for those two things? There isn't one, Go rant and rave at God, He designed the system. Sorry. Guys can stand to pee, girls get to carry babies. Facts of life. There happen to be some great benifits to the female plumbing, but not on cold winter nights, and not when 5 days overdue

. (and not when trying to convince an employer that you have no intentions of getting kids)
Now there are some people (male and female) who have no statistical reason, but will simply hire someone at the lowest rate they can get them to work for, which (statistically) tends to be less for women. Also some people DO still live in the dark ages and assume women can't do a certain job (some women assume men can't, not all of us are open to SAHDs, sheesh, half the mothers I know assume their own husbands can't do anything when at home, much less stay with the kid) This is not Universally true however.
Personally I think if you posted a series of articles about how women are paid equally, and gave a free course on negotiation and research of salories, you would prolly see a much faster trend to pay the same then the by harping on how it is different (reinforcing the employers opinion that women will TAKE less for a job)
BTW I am prejudiced, I don't want a male midwife!!!!!!!! Or labor nurse, a male CANNOT have a clue what it is really like!!!!!!! I personally don't want a labor nurse that has never had kids either, but I would prefer she at least knew what cramps were like than a guy who never had a cervex to be checked much less a contraction!