The police made the horrific find in an apartment on Rue de Bua in the 20th arrondissement, eastern Paris, on Friday morning.
The woman was several months pregnant, according to numerous reports in the French media. She had lacerations all over her body.
The man, believed to be her partner had also had his throat cut but survived. He was also wounded in the stomach.
He was said to be in a critical condition and had to be taken out of the building by firefighters via the window of the apartment on a stretcher and using harnesses.
According to Le Parisien an electric sander was found in the apartment close to the bodies.
It remains unclear if there were other people involved in the gruesome incident, but reports suggest there was a history of domestic violence in the couple.