Chicago ? There’s no medical reason to prevent healthy women in their 50s from turning back their biological clocks and having babies with donated eggs, researchers say in the biggest study of motherhood after menopause.

The study looked at 77 women who participated in the University of Southern California’s assisted-reproduction program between 1991 and last year. It found that there were no infant or mother deaths and no serious health problems in the babies.

The older women were likely to have Caesarean births and faced high rates of pregnancy-induced diabetes and high blood pressure. But those conditions are temporary, treatable and not reason enough to exclude them from trying to get pregnant, the researchers said.

Preventing them would be age discrimination, said Dr. Richard Paulson, who led the study published in today’s Journal of the American Medical Assn.

“Not only do I not have a problem in allowing them to become pregnant, I would have an ethical problem in denying them,” he said.

Women are not biologically designed to become pregnant after their bodies stop releasing eggs. This occurs on average at age 51. But with baby boomers leading longer, more active lives, 51 is not as old as it used to be. And more and more women who postponed motherhood until it was too late to get pregnant with their own eggs are choosing test-tube fertilization with eggs donated by younger women.

Some doctors worry that because of the older women’s advanced reproductive age, pregnancy might be dangerous for them or their babies.

Some also say it is unethical to allow women to become pregnant if they might not live to see their children grow up. The American Society for Reproductive Medicine’s ethics committee says egg donation for postmenopausal women should be discouraged.

In the study, the older women’s rates of pregnancy – 45 percent – and multiple births – 30 percent – were similar to those in women a decade or more younger who become pregnant with donor eggs. So was the birth rate – about 37 percent.