It was not the easiest thing. Maybe it is, maybe not. There are more companies, so more females, so more marriages, or at least babies. I wonder if that might have anything to do with it. Yeah, there is some sort of legal protection for pregnant women but there are ways to skirt this.
Any company can build up a case against an employee based on many other issues.
I did read Kent's book. And she still danced after each one. Speaking of which, Balanchine adored his women. This is not good. Yes, dancers should be allowed to perform when pregnant.