A US teenager has been charged with first-degree murder after she killed her newborn son as the baby looked like her ex-boyfriend.

Ana Rosa Mora, 18, was a high school student in Chicago who gave birth to the baby boy. However, soon after realising that the baby looked more like her former lover, the teenager decided to wrap the newborn in a plastic bag and leave him outside to die, for fear of separation from her current boyfriend.

Mora downloaded pictures from the internet and passed them off as those of her baby's to mislead people in school who knew she was pregnant. Nonetheless, the staff members of the school grew suspicious of Mora's behaviour when she enquired whether the police had the right to conduct DNA tests linking her to the dead child, reports Chicago Tribune.

The school staff alerted the police.

When a construction worker discovered the little one wrapped in a plastic bag lying in the street, the infant had already died, possibly due to asphyxiation, authorities say.

Initially, Mora denied the dead infant was hers but later admitted to her actions.