An 18-year-old man, accused of stabbing a pregnant Calgary mom and pushing her down a flight of stairs, has pleaded guilty to the crime.

On Thursday, Isaiah Rider admitted in court that he killed Christa Cachene inside her Ranchlands home following a house party in 2015.

In an agreed statement of facts, released in court on Thursday, Rider said he got into a fight with Cachene, a 26-year-old mother of two.

He said he stabbed her and pushed her down some stairs.

Experts say the blunt force trauma inflicted by the fall, not the stabbing, was what killed her.

Cachene’s father, who was taking care of her two children, discovered her body inside the home.

Rider was charged with second-degree murder in the death but pleaded guilty to manslaughter.

He will be sentenced in October.