A Des Moines baby sitter accused of killing a toddler claims an abortion intensified years of depression and left her unable to control her anger.

Tifany Myers, 18, does not admit fatally slamming 21-month-old Joel Vasquez to the floor in January. But her lawyer argued Thursday that the abortion - performed two days before the boy suffered severe head injuries - triggered emotions similar to postpartum depression.

Myers was scheduled to go on trial for first-degree murder Monday. The trial will be postponed for at least six weeks to give lawyers time to prepare for the unusual defense.

Attorney William Kutmus insisted Myers' mental state lessened her responsibility in the boy's death. "This isn't creative stuff," he said. "Remember, it's depression."

If a jury believed Myers' defense, she could be found guilty of lesser charges but not first-degree murder, Kutmus said. Her inability to process information would rule out premeditation.

After calling 911 in January, Myers told Des Moines police she thought the toddler fell from a bed. Police allege Myers later said she threw him to the ground when he continued to cry. The boy died on Jan. 21.

Michael O'Hara, a University of Iowa psychology professor, said postpartum depression rarely begins immediately after a live birth, let alone after an abortion. "I think it's going to be a stretch, quite frankly," he said. "I would be surprised to see it develop in that way, in that short a period of time. One could imagine this woman had all sorts of problems before."

Two area doctors evaluated Myers' mental standing, Kutmus said. Both found her to be severely depressed, both before and after the toddler's death. "She's of low intelligence, very nonaggressive," Kutmus said.

Myers' mother said her daughter never received treatment for depression. "She doesn't talk to anybody," Leslie Myers said. "She just keeps it bottled up."

Assistant Polk County Attorney Nan Horvat declined to comment.

Post-abortion syndrome is tinged with controversy. The Elliot Institute, an Illinois anti-abortion group, says abortion can cause serious psychological injury for some, with reactions ranging from regret to devastation.

Some abortion-rights groups dismiss that, and the American Psychological Association does not recognize post-abortion trauma as a genuine disorder.

Nancy Adler, a University of California at San Francisco medical psychology professor, said women can experience emotional difficulty before and after births, as well as abortions.