Large research universities with more money at their disposal are typically more generous with paid leave. Institutions like Harvard University, the University of California, and the University of North Carolina allow faculty women to take paid time off from teaching for an entire semester. But in many cases, exactly how much teaching relief a professor gets is up to the department chairman, who is responsible for finding someone to fill in while the new mother is away. Negotiating with department heads can be a difficult process for women who are untenured and may be reluctant to push too hard. I don't think as a junior woman you can go in and start raising the roof.
Some women find themselves pressured to use fellowships and sabbaticals as maternity leave.
One junior faculty member in sociology, who timed the birth of her baby for April, just as the quarter was ending, thought she would have this summer off and then have relief from teaching one course in the fall. But when she secured a fellowship that would give her relief from teaching a second course in order to do research, her dean pressured her to give back the teaching relief that the university had already awarded her. Only after the woman balked did the university agree not to renege on its original offer. She says she plans to use her fellowship to do research, and that is why she complained when the university wanted to call it a maternity leave. Some institutions do have policies that make new parents happy.