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But eggs proved more delicate and difficult to freeze than sperm or embryos. The problem: Eggs contain lots of water, and early methods of freezing and thawing allowed ice crystals to form that could destroy or damage them. In the past decade, scientists created a flash-freezing method called vitrification that appears to overcome that challenge.

For a number of years, egg-freezing has been offered experimentally for young women or girls who are diagnosed with cancer or other serious illnesses that would destroy their ovaries.

Then there’s age-related infertility: About 1 in 5 U.S. women now have their first child after age 35, according to the Centers for Disease Control and Prevention. Yet the ability to conceive begins dropping around 35 and more rapidly as the 40s near. Women have fewer eggs left, and these older remaining ones aren’t as healthy, meaning even if the woman can get pregnant she’s more likely to miscarry.

What’s involved in freezing eggs: Women inject high levels of hormones for a week in order to ovulate as many eggs as possible. Retrieving them is an outpatient procedure that can cost $10,000 to $15,000, sometimes not including the cost of the medication. Clinics also charge a storage fee, and then women who wind up using their eggs will pay thousands more to undergo in vitro fertilization.

There are no estimates of how many women have had their eggs frozen. But Pfeifer’s committee cited four well-controlled European studies that compared IVF using either fresh eggs or ones that had been frozen from younger women, and found the chances of pregnancy were comparable.

What about birth defects? There are only about 1,500 known live births resulting from frozen eggs worldwide, compared with about 1 million IVF births using fresh eggs. But a recent review of nearly 1,000 of the births from frozen eggs found no increased risk of birth defects, Pfeifer said.

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EDITOR’S NOTE _ Lauran Neergaard covers health and medical issues for The Associated Press in Washington.

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