An American woman has been arrested for stabbing a pregnant stranger before snatching her unborn baby from her womb.

Dynel Catrece Lane, 34, is accused of brutally attacking the victim, who was seven months pregnant, before tearing out her fetus, taking it to hospital and pretending she’d suffered a miscarriage.

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The 26-year-old victim was answering an ad for infant clothing Ms Lane had posted on classified listings service Craiglist when she was attacked.

She was taken to hospital after the Wednesday attack and managed to survive after being operated on.

“Officers entered the home and located a female who had been beaten and stabbed in the stomach,” local police spokesman Jeff Satur said.

“It was later learned, the female was pregnant and her baby had been removed. The victim was transported to the Longmont United Hospital where she underwent surgery and is expected to recover.”

The suspect “was located at the Longmont United Hospital with a deceased baby, reporting a miscarriage. The suspect and victim were not known to each other prior to this incident”.

Police on Thursday released a harrowing 911 emergency call in which the victim begged for help.

Satur said the suspect was due in court Thursday afternoon, facing a charge of attempted first degree murder.

—with AAP