A kiss before dying - Ira Levin

Dorothy, Ellen and Marion were three attractive sisters with a very rich father.
Dorothy meets a handsome young man with an eye for her inheritance while she is in her sophomore year.
They are to be married and her life will be blissful; but Dorothy is pregnant and her fiance's plans are ruined, for Dorothy would be disinherited if her father discovered the truth.
So the young man provides his bride-to-be with some pills that will solve the problem.
Soon there will be no baby - and perhaps no Dorothy either...