TAKAMATSU, Japan — The Kagawa Prefectural Central Hospital in Takamatsu is believed to have mistakenly implanted a woman with the in vitro-fertilized ovum of another patient in September, the prefectural government has announced.

The Takamatsu woman, in her 20s, who received the egg was receiving fertility treatments at the hospital and was expecting to be implanted with her own fertilized egg.

She became pregnant as a result of the procedure and had an abortion in the ninth week of the pregnancy, so the suspected mistake cannot be confirmed.

However, the doctor who performed the procedure has apologized over the matter.

The woman filed a damages suit against the prefectural government on Feb. 10 with the Takamatsu District Court, demanding about $215,000 for mental anguish.

Although in vitro fertilization becomes more common with every year, this would be the first instance of a woman becoming pregnant with the fertilized egg of another woman.

Dr. Kiyoya Kawada, 61, the physician who performed the procedure, told The Yomiuri Shimbun on Friday that there were imperfections in the hospital's procedures, and admitted he had not conferred with other staffers to confirm the egg he was going to implant was the correct one.

He said he had performed similar procedures without supervision or assistance for several years.

"I was overconfident about (my abilities)," he said.

Kawada said: "I'm very sorry that I caused the woman to become pregnant from a fertilized egg that was not confirmed as hers. It's a mistake I can't compensate for."

The error in question occurred on Sept. 18 when Kawada removed the woman's fertilized egg from an incubator to check its maturity. A petri dish containing the fertilized egg of another patient was already on the table at the same work station.

He worked alone that day although there were some technicians on duty.

Kawada labeled a petri dish with the woman's name, but he is believed to have mistakenly put the incorrect egg in the dish. The egg was placed in the woman's uterus two days later.

He said Friday that he could not offer any concrete reasons for the mistake, but that there were many possible contributing factors. He said he had diverged from standard procedure of handling only one patient's fertilized eggs in the lab at one time, and had been more focused on successful cultivation of eggs than on proper procedure.

Sources close to the prefectural government and the hospital said the woman began receiving fertility treatments at the hospital's obstetrics department in April.