By having her eggs frozen before she begins cancer treatments, a woman can preserve the hope of one day having a baby. Freezing eggs is one thing. Thawing them safely so they can lead to pregnancy is the challenge.

In the past, efforts to freeze a woman's eggs, or oocytes, have not worked well because the cells are large. When the egg is thawed, ice crystals cause damage that prevents the egg from being fertilised.

Researchers at the University of Michigan looked beyond traditional techniques to a method of freezing cells called vitrification. This cryopreservation technique allows the eggs to be cooled fast enough that the transformation from liquid to solid is instantaneous. No ice crystals form and the consistency resembles a viscous glassy state. Research so far has used mouse oocytes but U-M expects to make the technology available in the clinic soon.

"With traditional slow-freeze techniques, just over half the eggs survive the thawing process. Using vitrification, we are getting 98 percent survival. For a woman with cancer, these are the only eggs she's ever going to have, so it's important that as many as possible remain viable,” says Gary D. Smith, Ph.D., associate professor of obstetrics and gynaecology, urology, and molecular and integrative physiology.

Using mouse oocytes, 80 percent of eggs that had been vitrified became fertilised with a technique called intracytoplasmic sperm injection, with a live birth rate of about 30 percent, comparable to conventional IVF when eggs are not frozen. The fertilisation and birth rates for vitrified eggs are similar to the rates for control eggs that were not vitrified.

Guidelines for patients and physicians still need to be established as the technique begins to be offered in a clinic setting, Smith says. "This is a very new technology and it requires education both of patients and physicians,” Smith says.

MEDICA.de; Source: University of Michigan Health System