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New Egg-Freezing Process Could Preserve Fertility

Scientists inject a little sugar in the mix

FRIDAY, Jan. 11, 2002 (HealthDayNews) -- Injecting a sugar solution into human eggs before preserving them in liquid nitrogen could dramatically increase the odds that they will survive the freezing process, new research has found.

Although the results are preliminary, the findings could lead to techniques that help preserve fertility in women fighting cancer and other diseases, the researchers say.

"Science has always been interested in trying to find a way to store eggs," says Susan Lanzendorf, an expert familiar with the study in the January issue of Fertility and Sterility.

"We can very easily store sperm, which is good for men because if they should lose their ability to reproduce, then they can use that sample to have children. But there's no such thing readily available for women," she says.

"It would be very important if there were some way to store gametes -- the eggs -- for women," Lanzendorf adds.

In the freezing (or cryopreservation) process, sperm or embryos are commonly immersed in a solution containing a sugar called trehalose. This sugar acts as a protectant, helping the cell to survive the freezing process without drying out.

In the latest study, researchers at Massachusetts General Hospital in Boston speculated that injecting trehalose into an egg could prevent the damage that normally occurs inside the cell during freezing.

There have been limited cases of successful pregnancy after egg freezing, but the current success rates hovers around the 1 percent mark.

"That doesn't offer a very promising circumstance to a young person who would be interested in freezing their oocytes because of pending chemotherapy," says senior investigator Dr. Thomas Toth.

The problem with freezing eggs is that they are the biggest cells in the body, with a large amount of fluid inside their membrane. When the egg freezes, the fluid inside the cell can form harmful crystals that rupture the membrane.

Injecting the trehalose into the egg before freezing removes as much water as possible from the cell, reducing the risk that crystals will destroy the protective outer membrane.

A research team led by Toth compared three methods for freezing eggs. All of the eggs used had been harvested for use in in vitro fertilization, but had failed to mature or fertilize.

Toth, an assistant professor of obstetrics, gynecology and reproductive biology, divided the eggs into three groups. The first group was frozen without any treatment, the second group was frozen in a medium of trehalose, and the third group was injected with trehalose and frozen in a medium containing the sugar.

Different subsets of the each group were frozen to 5 degrees Fahrenheit, 11 degrees below zero, or 76 degrees below zero, then thawed at room temperature and cultured overnight.

All of the eggs frozen to 11 degrees below zero or lower degenerated. But in the eggs frozen to 5 degrees, 63 percent of those in a trehalose medium survived, compared to 22 percent of those in the sugar medium and 13 percent of those frozen without any treatment.

"The sugar molecules may be more beneficial than expected and may be helpful in protecting the cellular membrane as well as the cellular organelles," Toth says.

"This information may help us explore this technology and learn more to see if there could be an alternative to our standard treatments, which seem so limited," Toth says.

Embryos take better to freezing because they're made up of several small cells within one large membrane, and have more membrane than fluid. Sperm freeze very well because they have very little fluid within their membrane.

What To Do

Check out this FAQ on infertility from the American Society for Reproductive Medicine.

You can also read this article on egg and embryo freezing from or learn about the techniques used in embryo cryopreservation from Duke University.

SOURCES: Interviews with Thomas L. Toth, M.D., assistant professor, Department of Obstetrics, Gynecology and Reproductive Biology, Massachusetts General Hospital, Boston; Susan E. Lanzendorf, Ph.D., director, Basic Gamete and Embryo Research, Jones Institute for Reproductive Medicine, Eastern Virginia Medical School, Norfolk, Va.; January 2002 Fertility and Sterility
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