Nightborn (1970)

A couple’s dream of a perfect child spirals into a nightmare as soon as the baby is born. The mother Saga thinks there’s something seriously wrong with the child, who drains her of all energy and sucks blood from her breasts. While their marriage strains, Saga’s husband Jon tries to pretend he doesn’t see the problems, and Saga lets herself start hating the monster she gave birth to. Maybe the only way out is to become a monster herself.