If the premarital counseling is Catholic, it will also include some discussion of intimacy, natural family planning and birth control, etc. There are also discussions about what you expect from intimacy and things like that as well. Not something you want your mother/MIL at. And as somebody else pointed out, even the innocuous questions about expectations for married life are things that you don't want your mother/MIL hovering over you, making points, scoring one party against the other, and generally butting in over, not to mention the huge wealth of personal information she'd get from it. If she discovered that they wanted to wait for kids and then they had a honeymoon baby, she could have such fun crowing out their "accident" even if it would have never occurred to anybody else in their life that the baby was an accident. And even if it *wasn't*, they'd changed their minds!