CHATTANOOGA, Tenn. — A Tennessee mother accused of contributing to the deaths of her newborn twins by using drugs will not be prosecuted.

News outlets report that charges against 29-year-old Tiffany Marie Roberts were dropped Thursday in a Chattanooga courtroom.

Hamilton County District Attorney’s office spokesman Bruce Garner says the charges were dismissed because the medical examiner said the twins’ cause of death “could not be linked solely with Roberts’ alleged drug abuse.”

Roberts gave birth to twins in July at 23 weeks pregnant. Both infants died two days later. After the deaths, Roberts had been charged with first-degree murder, aggravated child abuse or neglect and viable fetus as a victim.

The hospital listed the twins’ cause of death as pulmonary hemorrhage. An official cause of death hasn’t been determined.