Gia Allemand -- Menstruation Made Her Suicidal ... Says Mom

Gia Allemand's mother believes her daughter's menstrual cycle was responsible for the extreme emotional turmoil that drove Gia to suicide last month.

Donna Micheletti -- who was on the phone with the former "Bachelor" star when she hanged herself -- described her final moments with her daughter to Dr. Phil, explaining Gia had a history of drastic mood swings around the time of her period.

Donna said, "At that point, with how she felt with her menstrual cycle, she could not see clearly ... It was like night and day. It would come out of nowhere. All of a sudden, something would click in there and she would say 'This isn't right. He doesn't love me.'"

Donna acknowledged that Gia had been upset for various reasons -- including recent fights with her boyfriend and father -- but believes the hormonal extremes are what ultimately drove Gia over the edge.