Ah! Thanks for correcting me on that @wraith808 - I had not known there was such a film, and thus assumed (apparently erroneously) that it was a spoof on "Rosemary's Baby". Your comment makes sense - e.g., I did wonder where the wicker baby basket came from, as that was not on the RB poster as far as I could recall (I last saw it many years back).
I looked up "It's Alive" on IMDB, and thought it seems like a silly horror movie. The theme of "a couple's infant child turns out to be a vicious mutant monster that kills when frightened" is replicated to some extent in the SF movie "Looper", where the boy child seems normal but is innocent and a telekinetic and cannot control his damaging powers when he is frightened. The surprising outcome in the story is that he is to be part of changed history (alternative futures) for the better.