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 fertilized.
U-M researchers 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 gynecology, urology, and molecular and integrative physiology at the U-M Medical School, and director of the Fertility Counseling and Gamete Cryopreservation Program at the U-M Comprehensive Cancer Center.
Smith will present results of his research on Sunday, May 29, at the World Congress on In Vitro Fertilization, Assisted Reproduction and Genetics in Istanbul, Turkey.
Cancer treatments such as chemotherapy and radiation therapy can cause damage to a woman's reproductive system and leave her unable to have chi ldren afterward. Some women may regain their reproductive function after their treatment ends and may be able to conceive on their own, while others will become infertile. Egg cryopreservation could be insurance for those women at highest risk of fertility problems after cancer treatment.
When a woman wishes to become pregnant, the vitrified eggs would be warmed and then fertilized with male sperm. The fertilized eggs would then be transferred to the uterus in the same procedure that's used successfully when couples freeze embryos.
When eggs are warmed after vitrification, fertilization rates with conventional IVF are low. Instead, researchers have found, a single sperm cell must be injected into a single oocyte, a technique called intracytoplasmic sperm injection, or ICSI. While ICSI is an established technique used in assisted reproduction, it is more complex and costs more than traditional methods.
Using mouse oocytes, 80 percent of eggs that had been vitrified became fertilized with ICSI, with a live birth rate of about 30 percent, comparable to conventional IVF when eggs are not frozen. The fertilization and birth rates for vitrified eggs are similar to the rates for control eggs that were not vitrified.
For egg freezing to work, it must be a mature oocyte, which means a woman must have 14 days of hormone treatments to stimulate mature egg production. This could limit its applications for some women. Researchers question if it is appropriate for women with cancers fueled by estrogen, such as breast cancer. In addition, the hormone treatments require delaying the start of cancer therapy, which may not be an option for every patient.
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.
U-M has cryopreserved eggs for one patient; h owever, the service is currently not offered while researchers seek approval for a clinical trial. A specialized clinic in the U-M Comprehensive Cancer Center provides counseling and information for women considering their fertility options, and the clinic currently freezes embryos for cancer patients who have a partner. The clinic also offers counseling and sperm freezing for male cancer patients. U-M will offer egg vitrification only to women facing cancer treatments, because the long-term safety of this technique remains unknown.
"In a woman with cancer, if she is going to lose her reproductive capacity because of cancer treatments, this is her only choice to have baby with her own eggs," Smith says. A clinical trial through the U-M Comprehensive Cancer Center is planned to begin by fall.