I'm searching for a short story where the mother considers the baby as an intruder trying to kill her. While I think it could be a Bradbury, it is quite possibly the work of another mid 20th century author.
If the author/title comes to anyone's mind, I would really appreciate it.
Definitely "The Small Assassin", yes... but the concept has been used by others, so it is possible you have seen a variation on the idea. Ray was aware that a number of mediocre films had borrowed the concept (and so did ROSEMARY'S BABY to an extent).
For fans of Ray Bradbury's brilliant story "The Small Assassin", the link below will take you to the cover of the November, 1946 issue of DIME MYSTERY MAGAZINE, which included the story. The cover art also illustrated Ray's story. That great cover was by artist Gloria Stoll Karn.