Police say a US woman who allegedly tried to end a pregnancy by punching herself in the abdomen and allowing a relative to sit on her stomach is now at the centre of a homicide investigation.

Reeta Yousif, 21, gave birth at a hospital in Nashville, Tennessee in March just 24 weeks into her pregnancy.

Her baby boy, who was not given a name, lived for less than two hours and died from blunt force trauma to the head.

On Friday (8 December), the Metropolitan Nashville Police Department said the boy's death has now been classified as a murder.

Investigators claim Yousif "hit herself in the abdominal area with a closed fist in order to terminate the pregnancy, and further allowed a young relative to sit on her stomach".

No charges have been filed against the woman, pending a review by the District Attorney's Office.

A similar case in January saw another Tennessee woman admit a felony count after attempting an at-home abortion with a coat hanger 24 weeks into her pregnancy.

Anna Yocca was taken to hospital after losing blood and her boy was born two weeks later weighing just 1.5 pounds.

He had a number of severe medical problems that may have been caused by the coat hanger.

The child was placed into the custody of the Department of Children's Services.

Yocca, 32, from Murfreesboro, pleaded guilty to attempted procurement of a miscarriage after an attempted murder charge was dismissed. She spent more than a year in jail.

In May, Tennessee Gov. Bill Haslam outlawed abortions after 20 weeks if a doctor determines the fetus is viable and won't seriously harm or threaten the life of the mother.