There have been two previous attempts to transplant a womb — in Turkey and Saudi Arabia — but both failed to produce babies. Doctors in Britain and Hungary also are planning similar operations, but using wombs from women who had just died.
Brannstrom said any woman in the study who does get pregnant will be on a low dose of drugs to keep from rejecting the transplanted womb and will be monitored as a high-risk pregnancy.
The transplants are intended to benefit women unable to have children because they lost a uterus to cancer or were born without one.
Some doctors said women who got pregnant with a new uterus would have to be watched carefully for how the womb progresses throughout pregnancy.
"There are questions about how the physiological changes in the uterus will affect the mother and whether the transplanted uterus will be conducive to a growing baby," said Dr. Charles Kingsland, a spokesman for Britain's Royal College of Obstetricians and Gynaecologists and a gynecologist at Liverpool Women's Hospital.
In a study published last week, Brannstrom and colleagues described the procedures used to transplant the nine wombs and said there were "mild rejection episodes" in four patients.
He said the transplanted wombs would be removed after a maximum of two pregnancies.