Research on production and theory of psychological thriller/horror films

What makes psychological horror films successful in the genre?
Can you give some theory research behind two films/directors who have worked in this genre?

How is pregnancy conveyed in films? What are the common tropes of pregnant characters? Is mental health portrayed well in typical horror films?

What are the 2 most common types of editing in these films? How can you build tension within the confines of one house?

How are period films set in the 1980s difficult to produce in the modern day? What difficulties might we face?