What does the movie "Being In It", which is also called "Baby Snatcher", mean? I can't quite understand it.

Plot summary——

Sarah is a young photographer who has been single since her husband died tragically in a traffic accident. She had to stay home on her last day before going to the hospital to give birth. The peace is interrupted by a knock at the door. There is a mysterious woman at the door. Sarah is immediately suspicious and refuses to let her in; however, the woman does not leave. Sarah became concerned and informed the police. Outside in the darkness, the woman stared at her through the large floor-to-ceiling windows.

When the police showed up, the woman had left. There was a commotion in the nearby urban area. The upset policeman hurriedly comforted Sara and left. Sarah locked herself in the house, unaware that the woman had entered. When she feels her first contraction, she fights against the one thing this crazy woman is desperate to take...

Extended information:

Video Released for LFF (La Fabrique de Films), it was selected as the best film at the famous "Spanish Horror Film Festival". The crazy female killer in the film is played by Beatrice Dalle from "Wild Rose of Paris" . The realistic special effects come from the creation of BR Films, the special effects production company that once produced "Killer 47", and the terrifying visual special effects are the work of special makeup artist Jacques-Olivier Molon.