In August a 39-year-old Georgia woman who had undergone premature menopause gave birth to twins and made reproductive history, becoming the first person in the western hemisphere to bear a child from eggs that had been frozen long-term in the laboratory. Though births from in vitro fertilization using freshly donated eggs are fairly common, the new breakthrough could allow females to "bank" their childbearing potential. The initial recipient used donor eggs, but if a woman of 25 wished to delay motherhood until her 40s, when fertility wanes, she could literally put her own eggs on ice. "We have leveled the reproductive playing field for women," says Michael Tucker, scientific director of Atlanta's Reproductive Biology Associates, which pioneered the technique. "We've allowed them to turn off their biological clocks."

Raised on a dairy farm in western England, Tucker, 40, holds a doctorate in reproductive physiology from the University of Birmingham but is not a physician. After several years of fertility research in London, Adelaide, Australia, and Hong Kong, he came to the U.S. in 1989—settling in Atlanta, where he lives with his wife, Elisabeth, and their three sons. He began freezing eggs in 1994. "I had no concept it would take off in such a big way," says Tucker, who spoke about his work with special correspondent Don Sider.

Since in vitro fertilization of newly harvested eggs is well-established, why freeze eggs?

First, in a donor situation it's a cost issue. If we can freeze and thaw eggs at our convenience, it cuts costs. In the past a donor would come in and deposit, say, 30 eggs, a few of which would be fertilized and implanted into a single recipient—the rest might be discarded. Now, with freezing, we can use the eggs more economically—take the 30 eggs from one person and use them over again for several different recipients. You need pay only one donor, and you save on the labor costs by performing only that one harvesting procedure. I'm sure my administrator will shoot me for saying this, but I think over time we can bring down the cost of a typical in vitro fertilization from $15,000 to under $10,000.

Second, we are now able to freeze eggs from women who are about to undergo chemotherapy or radiation for cancer therapy, which usually destroys ovaries. This will give a woman the opportunity to harvest eggs before treatment and have them preserved for use when she regains her health.

And there is another benefit. Right now there is a slight flaw in fresh-egg donation that does not exist in semen donation. All semen is frozen for at least six months before it's used. This lets you monitor donors for a latent HIV or hepatitis infection. Freezing eggs will allow the same screening.

You say that freezing eggs levels the playing field. How so?

Men go on producing semen and viable sperm up to age 60 or even 70. With women, once they're past menopause, that's it. A lot of women tend to assume that menopause hits at about 50, but what happens in reality is that you get to 35 and the quality of your eggs and the number you produce start a massive nosedive. Now a woman can have her eggs harvested when she is 25 to 30 and store them until she is ready for children.

How long can an egg remain frozen and still be thawed and used?

Probably forever. Studies done with the embryos of cattle and mice show they're still perfectly viable after being frozen for decades. Frozen semen lasts just as long.

How much interest have you had from women hoping to pursue this?

All I know is that the girls at the front desk of our office said, "You owe us big-time—the phones have been ringing off the hook."

What about the ethics of this? Is there a risk of economic abuse?

There is the potential for some clinics out there to exploit the situation—but it's sure as heck not going to be us. There's no way I want younger women to panic and think, "What if I'm going to be left on the shelf?" and suddenly you get this horde of 25-year-olds crowding into infertility clinics to freeze their eggs. If a clinic tried to profit by encouraging this sort of panic, I would like to think the American Society for Reproductive Medicine would condemn them.

What about eugenics—that a society might use this technology to create an "ethnically pure" race?

I don't see it as a great threat. But while we scientists push this envelope of technology, the ethics and morals of it are not just our problem. It's up to all of us to be aware of potential abuses. Still, we in the scientific community police ourselves incredibly well. For example, we developed technology to predetermine the sex of embryos. But our clinic said, "Forget it. We don't want embryos of the 'wrong' sex to be discarded." We will sex embryos only for medical reasons—to avoid sex-linked disorders such as hemophilia.

Do you ever say to yourself, "Michael, you're playing God"?

I do my best to help the couples we treat—to provide good patient care. I'd like to think that what we're doing, as much as anything, is God's work.