(CNN) A Chattanooga, Tennessee, woman was charged with first-degree murder after her prematurely born twins died with narcotics in their systems, authorities said.

Both infants tested positive for several drugs, including cocaine, when they were born July 21, according to the affidavit filed the arresting officer. They died two days later, within hours of each other.

Tiffany Roberts, 29, admitted to investigators to taking drugs, "citing she has a problem," the affidavit said.

Medical staff at T.C. Thompson Children's Hospital at Erlanger told investigators that during her pregnancy, Roberts tested positive for cocaine, oxycodone, roxicodone, methamphetamine and benzodiazepines in drug tests administered on June 27, July 20, and July 21, the affidavit said.

Roberts told investigators she took ecstasy on July 20 and went to the hospital after being short of breath, according to an affidavit. She gave birth prematurely the next day, after 23 weeks of pregnancy, the affidavit said.

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