But then we have no idea how those vaccines will work in the real world where, when we need N% immunity achievement for herd immunity, a >N% of the population is not considered healthy (and also haven't been proven safe for). There have definitely been cases in which pregnancy is excluded from studies to prove safety with horrible consequences to pregnant people and their children.
Of course we're gonna test this on the healthiest, least-likely-to-accidentally-die humans, what's the point?
They explicitly did a pregnancy test on everyone who can be pregnant to preclude the possibility, just in case.