A woman whose ovaries ceased to function almost three years ago has given birth to a healthy 9-pound girl, baffling doctors at three hospitals.

"It is impossible, impossible," the 35-year-old woman quoted one of the doctors as saying when he detected a fetal heartbeat.

In effect, the birth took place after the woman, who asked not to be identified, had gone through menopause, her doctors said.

The woman's menstrual periods stopped three years ago and a physician at Kaiser Hospital diagnosed premature ovarian failure, an early menopause in which the ovaries stop producing eggs.

The doctor said she "didn't have anything to worry about as far as getting pregnant is concerned," she recalled.

A year later, Dr. Jeffrey S. Rakoff, director of the Scripps Clinic Medical Group's Fertility Center, confirmed the diagnosis of premature ovarian failure.

Then, during a regular checkup, Rakoff discovered the woman was six months pregnant.

Rakoff said neither he nor Dr. John J. Willens, the University Hospital physician who delivered the baby on Aug. 18, had ever heard of birth by a woman with a well-documented case of premature ovarian failure.

The birth is further confounding, doctors said, because the woman was taking medications commonly given women after menopause that also act as contraceptives.