A pregnant woman who killed her attacker said a maternal instinct helped her fight off the woman who investigators believe was after her unborn child.

"I do believe that I fought harder because it was for my child," Sarah Brady (search) told ABC's "Good Morning America" in interviews aired Sunday and Monday. "It is a maternal instinct to protect your child to the very end."

Katherine Smith (search), 22, died Thursday after luring Brady to her apartment to pick up a package supposedly delivered to the wrong address. When Smith pulled out a knife and attacked the pregnant woman, Brady fought back, striking Smith on the head with an ash tray and stabbing her three times with her own knife, police said.

Brady, 26, said she didn't know Smith before the two met at Smith's apartment and can't be certain why Smith wanted to kill her.

"I really am not sure what was going through her mind," Brady told ABC. "The only thing I thought was that she was going to kill me and my child and that is the only thing that ran through my mind."

Police said Smith passed herself off as pregnant by wearing padded maternity clothes and carried an ultrasound picture of someone else's twins. Inside her apartment, they found a baby nursery and a variety of surgical equipment that police said could have been used in delivering a baby.

"She was mentally disturbed," Fort Mitchell police Sgt. Tom Loos said of Smith. "There is no question about it."

Loos said that when Brady ran out of the apartment and flagged down a passing motorist for help, Smith removed her maternity underwear stuffed with padding and called 911. Dispatchers kept her on the line until she lost consciousness.

Smith bled to death. Police described Brady's wounds as cuts to her hands.

No charges had been filed against Brady, and Commonwealth Attorney Bill Crockett said he hadn't decided whether to present the case to a grand jury.

Several pregnant women have been killed in recent years by attackers who then removed their fetuses, in some cases to pass the children off as their own.

In December, a Missouri woman was strangled and her baby was cut from her womb. The baby was later found alive, and a Kansas woman was charged with kidnapping resulting in death. In 2003, a woman was shot to death in Oklahoma, allegedly by another woman who then pretended the 6-month-old fetus was her child. That fetus died.

Brady, who is nine months pregnant and due with a girl any day, said the baby is a blessing.

"I think I'm extremely lucky," Brady said. "I'm just glad I that I made it out with my baby alive."