otterbaby

I remember seeing a movie years ago on TV. It was an old black and white fild possibly from the 30's, maybe 40's and I was trying to remember the name of it. What I remember about it was... this older man lives with his much younger wife on a farm. She ends up having an affiar with his son(her stepson) who is closer to her age. She ends up having her husband's baby but, ends up smothering it with a pillow so she could be with the stepson. Any ideas? Thanks!