Li Xiaohong, director of the hospital's Reproduction and Genetics Center, said the groundbreaking operation included freezing human eggs, thawing them, fertilizing them and then implanting the eggs in the patient's uterus.

So far, six women have successfully conceived through such operations at the hospital, Li said, adding that two of them should be giving birth in May.

One of the mothers is expecting twins, the doctor said.

For years, scientists have been able to thaw frozen sperm and, more recently, have reported success at thawing frozen human embryos. But finding a way to freeze and thaw human ova successfully has been difficult.

Less than 100 women worldwide have been able to become pregnant by using frozen eggs, said Li.

The problem has been that human eggs are much larger and contain more water than sperm or embryonic cells.

As a result, there's much more risk of crucial chromosome-laden fibers within the eggs being damaged by frozen water crystals.

Li said her center had a 96 percent egg survival rate after the thawing-out process, a surprisingly good record compared to the rest of the world. Fertilization rates for frozen eggs are nearly as high as for fresh ones.

But she admitted the average survival rate may be lower since the technology differs from hospital to hospital and the condition of the eggs can vary from woman to woman.

She said the concept of egg freezing might have a far-reaching impact on how and when people choose to become parents, with the benefits of the technology extending beyond infertile couples.

Young women who have not found their ideal husband or want to spend more time building a career will now be able to set aside eggs and make a decision to have a child years down the line.

Young women diagnosed with cancer might gain an option for having children later in life instead of simply resigning themselves to infertility from radiation or chemotherapy treatments.

“The prospect of an egg bank is very bright since it could allow women to preserve their eggs,” said Li.

Although the doctor refused to reveal the fee for egg preservation, experts estimate the charge is not likely to be cheap.

In Argentina, the price for preserving eggs is about US$830 a year per woman, relatively expensive for a middle-income person in a developing country.

Li said the management of eggs is very important for an egg bank since the concept of egg freezing throws new wrinkles into the right-to-life debate.

"All the operations need to be done within the scope allowed by laws and regulations," said Li.

Meanwhile, much more study is needed before egg freezing becomes routine, she noted. The success of using frozen eggs is just a preliminary step and a great deal needs to be done to confirm the procedure is effective and safe, said Li.

(China Daily March 30, 2004)