People who get pregnant get paid time off from work. There is no real cap on the number of times you can take that paid time off, provided you've got the lump to show for it. (Can you imagine the fall-out from suggesting one of your direct reports ought to stop getting knocked up so often?)
So. Pregnancy is rewarded with vacation time.
Why is breeding a rewarded business behavior? Here's a more fair solution: Everybody gets an additional 30 days paid vacation per two years.
Or, pregnancy leave is unpaid. After all, you are not doing your job, nor are you being rewarded for your achievements. How many of these women actually come back to work afterwards anyway?
Ask yourself: Why is it a right to contribute to over-population? Why should your company be obligated to pay you to do it? (Contribute to over-population, that is. What sense of "do it" were you thinking?)