PITTSBURGH — A woman accused of cutting a baby from the womb of a pregnant teenager has a delusional disorder that rendered her legally insane at the time of the killing, a defense psychiatrist testified Thursday.

Dr. Barbara Ziv said Andrea Curry-Demus had a "break with reality" and was long preoccupied with pregnancies and babies.

Throughout her life, Curry-Demus claimed to have had miscarriages and a baby who died of sudden infant death syndrome, Ziv testified.

"None of this is consistent with reality," Ziv said.

Curry-Demus' bench trial began a week ago. Defense attorney Christopher Patarini is trying to convince the judge that Curry-Demus is not guilty by reason of insanity.

Closing arguments are expected today after the prosecution puts on the stand a psychiatrist to rebut Ziv's testimony.

On Thursday, Ziv said the disorder is rare and difficult to diagnose, which could account for various other diagnoses doctors gave Curry-Demus over 20 years. Despite the disorder, Ziv said, Curry-Demus is largely able to function.

Prosecutor Mark Tranquilli admits Curry-Demus has mental problems, but contends she was able to form the specific intent to kill required for a first-degree murder conviction by luring Kia Johnson, 18, of McKeesport to Curry-Demus' suburban Pittsburgh apartment in July 2008.

That's where, prosecutors say, Curry-Demus gave Johnson sedatives, bound her with duct tape and cut the baby from Johnson's womb before wrapping Johnson in plastic wrap, trash bags and more duct tape. Johnson died of suffocation and blood loss.

Curry-Demus then tried to pass the baby off as her own until suspicious doctors alerted police at the hospital where she was taken after claiming to have given birth, according to the prosecution. Johnson's body was found behind a headboard in Curry-Demus' bedroom; the baby survived and is living with relatives.

Curry-Demus met and befriended Johnson at the Allegheny County Jail, where Johnson was visiting her unborn son's father and Curry-Demus was visiting her husband.

"It is bizarre that a woman ... not under the influence of drugs or alcohol and not under a known psychological stressor ... would give a nonvoluntary Caesarean section to a woman," Ziv said.