I'm not sure what 'ost American horror story' is supposed to be. If we assume it's related to American Horror Story, that show has been evolving and presenting different horror ideas over time, but it's not something brand new in the grand scheme of horror as a whole. There are always new shows and movies trying to bring fresh takes on horror, but American Horror Story has been part of the established horror television landscape for some time.
There was a new horror story about a haunted hospital. The hospital had been closed for years due to a series of mysterious deaths. A journalist named Tom wanted to get a scoop on the story. He managed to break into the hospital at night. As he walked through the dimly lit corridors, he heard the sound of a gurney being pushed. But there was no one in sight. He entered an operating room and saw bloodstains on the table. Suddenly, the lights went out. He could feel a presence right behind him. When he turned around, he saw a figure in a doctor's coat, but the face was hidden in the shadows. He tried to run but kept running into dead - end corridors.
The 'new mother horror story' might involve external factors too. For example, she could be in a new neighborhood or living situation where she feels threatened. There could be a sense of isolation if she doesn't have a good support system. It could also be related to the pressure of being a 'perfect' mother that society often imposes, and the fear of failing in that regard.