Warning: This story contains details that may be disturbing.

The case of a mother and daughter who allegedly strangled a Chicago teenager and cut out her fetus is at least the 45th instance of this type of crime—which is usually fueled by desire for attention or fear of losing a male partner, according to an expert who has studied the phenomenon for years.

These fetal abductions are so brutal—and so easily solved—that conventional wisdom holds that the perpetrators must be psychotic, plunged into mental illness by a recent miscarriage or a long struggle with infertility.