The Fukuoka Prefectural Police said Monday that the head of a hospital and two other doctors have been referred to prosecutors after a fertility operation led to a woman's death in 2016.
The woman, who was in her 30s, died in December 2016 after undergoing an operation to treat ovarian congestion known as a Rubin's test. The operation involves inserting carbon dioxide into the uterus and through the fallopian tubes while the patient is under anesthesia.
The procedure took place the previous month at St. Mother Hospital in Kitakyushu.
Some of the gas is suspected to have entered her blood vessels and reached her lungs, killing her, according to investigative sources.
Medical experts said colored water, not air, is usually used in the medical procedure and that it is rare for patients to die during such treatments.
The doctor who conducted the operation has admitted to making a mistake. Police believe another doctor involved and the hospital chief bear responsibility for her death.
The hospital, known for conducting highly specialized fertility treatment that has attracted patients nationwide, said it will fully cooperate with the investigation.