The gender pay gap thing is just dumb anyway. If I run a company, and I could save ~25% by just hiring women, why wouldn't I do that? We should see men having a hard time getting employment if this were the case, but it's not.
The key is maternity leave; during a woman's career she can fall pregnant at any time, and her already having children is no predictor of lack of future children, nor is her marital status any real indication either.
A company is on the hook for an unproductive (read: absent) employee for 6 months (or more) at their current salary, and this can happen more than once. If this doesn't put downward pressure on women's salaries I don't know what else will.