Rosemary's Baby (1968), directed by Roman Polanski.
A young couple move into a spooky old apartment building. The other tenants are eccentric older people and we have a continuous stream of weird hints and intimations, including outright satanic chanting nearby. Mia Farrow dreams of being raped by a demon ("This is no dream! This is really happening!") and wakes up with scratches. We understand husband John Cassavetes, a struggling actor, has joined in a conspiracy to make her a bride of satan.
Her pregnancy is painful and she is sickly for a long time. As she figures it out (the audience is miles ahead of her from the very beginning) she tries to break away but the net grows tighter. She has the baby and the film ends with a satanic Nativity scene, which is surprisingly ambiguous: is this the triumph of evil or will a mother's love have power to defeat the devil?
Well done, all around. At the outset the camera is constantly moving, ungrounded, but seems to become more fixed toward the end, as if presenting an inevitable fate. Maybe a bit long at 136 minutes; about 90 minutes is just the suspense of watching her discover the truth that we already know. Actually, she never does figure it out: she thinks witches want her baby for a sacrifice.
It's a women's horror film: pregnancy is scary, as is the prospect of a disloyal, manipulative husband.
Cassavetes is devilishly fine as the seduced, lying husband. Ruth Gordon is a hoot as a brassy satanist. Once we understand, a lot of the little quips are darkly funny.
As with many 1960s movies, my first exposure was via the Mad Magazine parody, "Rosemia's Boo Boo", caricatured with devastating wit by Mort Drucker. I should hunt down some of the movie compilation books.