LONDON (AP) -- Doctors in Saudi Arabia have performed the first human uterus transplant, which produced two menstrual periods before it failed and had to be removed.

The experiment indicated a womb transplant is technically achievable, but experts say it is highly risky and ethically questionable. Some say it won't be practical until less toxic anti-rejection drugs become available.

The idea of uterus transplants was first explored in the 1950s. But after 20 years of failed experiments on dogs and baboons, many scientists considered it impossible because of the complex blood vessels that must be connected and because of fears that anti-rejection drugs could harm a fetus.

Dr. Wafa Fageeh, a professor at Abdulaziz University who performed the transplant with her team at King Fahad Hospital and Research Center in Jiddah, Saudi Arabia, called the operation ``a good start.''

``It is technically feasible, theoretically desirable, but presently unsafe,'' said Roger Gosden, a fertility pioneer at Eastern Virginia Medical School in Norfolk, Va. ``Their results reveal the risks and this procedure awaits the development of safe immunosuppression.

``A transplant to save life is an acceptable risk, but not one for fertility, when there are alternatives,'' he said. ``This is why we would never be given ethical clearance to try this in the United States'' for the foreseeable future.

The operation, reported this week in the International Journal of Gynecology and Obstetrics, failed because a blood vessel supplying the uterus developed a clot, which cut off the blood supply.

``You have to give them credit. They took a concept that everybody thought was undoable and they did it,'' said Dr. Louis Keith, an obstetrician and gynecologist at Northwestern Memorial Hospital in Chicago who was not involved in the research.

``It brought enough blood to the uterus for the uterus to survive 99 days and function as a uterus is supposed to function -- which is to menstruate,'' said Keith, who is assistant editor of the journal that published the report.

The transplant, using the womb of a 46-year-old post-menopausal woman who had to have a hysterectomy, was performed April 6, 2000, on a 26-year-old Saudi woman who had lost her uterus because of excessive bleeding after childbirth.

The recipient was given anti-rejection pills, but nine days after the operation the body rejected the womb. However, doctors were able to control it with drugs.

Hormone treatment was given to thicken the womb's lining and it grew to 18 millimeters thick, indicating that hormones were getting through and that blood supply was good, the researchers reported.

Menstrual periods happen when the lining of the womb, prompted by hormones, reaches a certain thickness to accommodate a fertilized egg but sheds because fertilization has not occurred.

The hormone treatment was given for 21 days, then stopped for a week before being restarted.

``She had two menstrual periods after stopping the hormones each time,'' Fageeh said.

On the 99th day, scans revealed a blockage in one of the grafted vessels which cut off blood supply to the uterus, and it had to be removed. The clot did not endanger the woman's life.