But there's another pregnant meaning "Of an argument, proof, piece of evidence, etc.: compelling, cogent, convincing; clear, obvious".
She cold was, and withouten sentement… And this was hym a pregnant [v.rr. preignant, prygnant; preuaunt] argument That she was forth out of this world agon. - Chaucer Troilus & CriseydeThis is from French pregnant "compelling, pressing" from prembre "to press" from Latin premere "to press". From an early date it was influenced in spelling and meaning by the other pregnant.
Rosenberg's style hangs on his prose like a maternity dress, concealing a not particularly pregnant argument. - British Journal of the Philosophy of Science 34 412, 1983