The Big Chill
The most promising of the new techniques, egg freezing, has been around for more than two decades—the first child to result from a frozen egg was born in 1986. Egg freezing—the scientific name is oocyte cryopreservation—used to be offered almost exclusively to young women whose reproductive future was threatened by illness (usually cancer) or its treatment (surgery, chemotherapy, radiation). Success rates were low. But as the freezing technique has been improved, it’s increasingly being offered to women who want to delay childbearing while they pursue demanding careers or wait to find the right partner. Although the American Society for Reproductive Medicine (ASRM) still labels egg freezing “experimental,” approximately 1,500 cryo-egg babies have now been born worldwide.
Because clinics do not yet have to report egg freezing cycles to the CDC (Centers for Disease Control and Prevention), there’s no accurate count of how many clinics are doing the procedure. Experts guess between 40 and 50, although more than half of all fertility clinics may be offering the services (and sending patients elsewhere for it).
Developing a way to safely freeze eggs proved more challenging than freezing either sperm or embryos. The older, slow-freeze technique created ice crystals, which destroyed many of the eggs when they thawed. Pregnancy rates were so low that egg freezing was not considered a viable means of fertility preservation until recently.
Some important developments in the field came from Italy, where the law, influenced by the Roman Catholic Church, prohibits freezing embryos but allows sperm and/or egg freezing.
But the biggest breakthrough came from Japan, where scientists developed an improved freezing technique called vitrification that surmounted most of the challenges and gave egg freezing new scientific legitimacy. In this process, moisture is removed from the eggs, and an anti-freeze chemical is added before flash freezing. That prevents ice crystals from forming, leaving a larger number of viable eggs. “Egg freezing is becoming more and more popular because the new technology of vitrification is extremely reliable,” says Sherman J. Silber, M.D., head of the Infertility Center of St. Louis at St. Luke’s Hospital, St. Louis, Missouri, and author of How to Get Pregnant (Little, Brown and Company, 2007).
The benefits are clear. Recent data show that 80 percent of eggs frozen through vitrification survive thawing, and pregnancy rates are now around 45 percent. Some individual clinics are even exceeding that number. New York University, which uses both slow freezing and vitrification, published data last year showing a pregnancy rate of 57 percent, higher than the national pregnancy rate of conventional in vitro fertilization (IVF) using unfrozen eggs. And Reproductive Biology Associates in Atlanta, which presented data at the recent meeting of the ASRM, boasts a 90 percent egg survival rate after thaw and a 65 percent pregnancy rate.
Having one’s eggs frozen is not a casual—or cheap—procedure. The process starts out just like the technique to harvest eggs for IVF: A woman injects herself with hormones to stimulate egg production. Then a doctor uses a needle to extract the eggs before storing them in liquid nitrogen until they’re needed.
For the best chances of success, patients 35 or younger should have 12 eggs on ice to get a 50-50 shot at a live birth; patients ages 36 to 38 need 16, says Kevin L. Winslow, M.D., director of the Florida Institute for Reproductive Medicine. That means women may have to go through the whole process several times to put away enough eggs. Counting costs for ovary-stimulating medications, tests, egg retrieval, yearly storage, then thawing, fertilization, and transfer, egg freezing can easily cost $10,000 for each cycle.
The younger a woman is when she freezes her eggs, the better her chances of eventually taking home a baby. Some experts foresee a day when women in their 20s will routinely be given the option of freezing their eggs so that if they wait until their 30s—or beyond— to procreate they’ll still be giving their babies the health advantages of younger eggs.
There are other uses for egg freezing besides preserving fertility for individual women. As the technology keeps improving, there will undoubtedly be more egg banks created to enable infertile couples, gay male couples, and others their shot at parenthood.
Stopping the Fertility Clock With New Techniques|
May 28, 2010
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