PITTSBURGH—A Pittsburgh woman who fatally stabbed her boyfriend last year was acquitted of third-degree murder and manslaughter charges after telling the jury she was defending herself during an altercation while she was seven months pregnant.

Ashley Wilson told jurors her boyfriend, 22-year-old Marquis White, was attacking her inside the apartment they shared when she grabbed a kitchen knife and stabbed him in the chest on May 22, 2011.

Wilson said she was only trying to fend White off because she feared for her safety and that of her unborn baby. She said she didn't mean to kill White, just fend him off.

Prosecutors had argued Wilson wasn't justified in using deadly force.

Wilson said the fight began after she spotted a photo of a nude woman in White's email.