I'm taking a wild guess that almost every horror fan has heard or seen the 1968 classic Rosemary's Baby starring Mia Farrow, which is one of the scariest films ever made. The movie is an adaptation of the 1967 novel of the same name by Ira Levin.
I had stumbled up on Rosemary's Baby while searching for a novel to read for a book report for an English class during my freshman year of high school in the mid-1990s. Originally, the book belonged to my grandmother, who had moved away after the death of my grandfather, and most of her books were being stored at my parent's house. It was a first-print hardback edition minus the original cover jacket. I still have this book as well as "The Stephen King Horror Library" edition.
Shortly after reading the book, the movie adaptation aired on TNT late at night. I recorded it on a VHS (Remember those?) and I later watched it. It's one of the best book-to-film adaptations ever produced as it goes exactly by Ira Levin's original story.
Rosemary's Baby is a psychological horror tale centered around Rosemary and Guy Woodhouse, a newly married Manhattan couple who move into a new apartment building, the Bramford, which has a deadly past involving witchcraft and murder. Usually, this would be a turn off for just about anybody else but Guy and Rosemary don't believe in superstitious. Shortly after moving into the apartment, they meet their odd elderly neighbors - Roman and Minnie Castevet.
While not planned, Rosemary becomes pregnant after having a bizarre nightmare involving a satanic ritual. Being young and naive, she takes advice from the Castevets and uses their doctor - Dr. Abraham Sapirstein, who insists she should drink homemade "health" drinks made by Minnie instead of taking prenatal vitamins. Let's just say the next few months aren't very good experiences for Rosemary. Instead of gaining pounds like all expecting mother's do, she quickly loses weight near to the point that she almost resembles a skeleton. Plus, she has a horrible pain coming from her womb. Over time, the pain magically disappears and she puts on baby weight.
With her due date just around the corner, Rosemary learns her neighbors are not who they say they are and that her unborn child is in danger.