Trying to find a 1970S horror film

[Tessi Dietrich]

The opening scene is of a pregnant woman who gives birth via caesarean section. The doctor puts the scalpel into a candle flame. It's shown or maybe just assumed that the baby has died.

We then cut to present-day late-1970s and the movie unfolds. I don't remember the rest of the movie, but the ending shows a female protagonist in the attic and the killer is revealed to be a guy in what I recall as a porcelain jester mask who uses a sort of walking-stick to kill.

I'm pretty sure it was a mid or late-70s American horror film. I accidentally taped it off British TV around 1993 when taping Halloween (1978).

I have tried using IMDB advanced search, but no luck.

Any thoughts what this movie is?

Cheers!