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.

According to the hospital, Kawada had provided fertility treatments such as in vitro fertilization without supervision or assistance from 1993 until two other technicians joined him in 2002.

Fertilized eggs are currently handled at the hospital by Kawada and four technicians. However, the technicians are often engaged in other duties when Kawada works with the eggs, the sources said.

Kawada said, "I cultivated fertilized eggs alone on the weekends when the technicians were off, and I often worked alone even on weekdays."

He said he felt responsible for the incident, and that he should have worked more closely with colleagues. He said he would discuss the issue with the director of the hospital.

The hospital was aware that Kawada frequently worked alone, but did not regarded the situation as problematic because he had performed about 1,000 in vitro fertilization procedures.

Yuzo Matsumoto, director of the hospital, said, "We believed the situation was all right because such an incident has never been known to occur before."

Shigeo Araki, director of International Institute of Medical Technology, a research group based in Utsunomiya, said such incidents could be prevented by ensuring doctors in charge of patients are familiar with and follow clear-cut procedures.

The woman who had been undergoing fertility treatment was forced to make an agonizing decision shortly after becoming pregnant after she learned that she had been implanted with the wrong egg.

During a press conference Thursday, Matsumoto said the woman began taking external fertilization treatment at the hospital last April because she had been unable to become pregnant after a year of treatment at a private hospital in the prefecture.

The woman was delighted on Oct. 7 when Kawada told her she was pregnant.

But the situation changed a month later, when on Nov. 7, Kawada and the head of the hospital's obstetric department told the woman and her husband that it was likely the egg was not hers.