Cryopreservation techniques have been offered in assisted reproduction programs for some time now. Freezing sperm for men who want or need that option has been available since it was first introduced in 1992.1 Most men who decide to bank their sperm want to protect them from the potential damage of cancer treatment. The sperm are later thawed and used in in-vitro fertilization.2 Embryo cryopreservation is also available currently for couples using assisted reproductive technologies (ART). Evidence has shown that transferring multiple embryos does not improve a woman's chances of pregnancy. It only increases her odds of having a multiple pregnancy. Thus, embryo cryopreservation is an option when there are additional embryos not transferred for pregnancy.3
Women undergoing cancer treatment or facing increasing age also want an option to preserve their fertility for future use. But freezing eggs is a more challenging endeavor, experts point out.4
The Fragile Nature of Eggs
Cryopreservation involves deep freezing eggs, sperm or embryos in liquid nitrogen. Currently, embryos and sperm are frozen most often, and the process is more common in fertility clinics that also offer in vitro fertilization (IVF). In egg freezing, a woman's ovaries are artificially stimulated to produce eggs. When the eggs mature, typically within 12 days of the start of a cycle, they are retrieved using ultrasound guidance and then frozen for later use.
However, since the cells that make up eggs are more delicate, eggs are more susceptible to the damaging effects of freezing than sperm. While the first reported pregnancy from egg freezing was reported in 1997,5 medical experts don't yet regard this application as routine.
"An egg tends to be a lot more sensitive to the cryopreservation and the freezing temperatures than an embryo is," explained Said Daneshmand, MD, a reproductive endocrinologist at The Fertility Center of Las Vegas, a Nevada fertility clinic. "The embryo tends to be much more resilient to the freezing process."
When an egg undergoes cryopreservation, the resulting crystallization increases the chances that the egg will become damaged during the process, he said. As a result, the odds of pregnancy success using frozen and later thawed eggs range from about 20% to 40%. Compare that to success rates using frozen embryos that vary from 70% to 80%, said Daneshmand, who is also an associate professor of Reproductive Endocrinology and Infertility at the University of Nevada School of Medicine.
Widening Options for Women in ART
Despite these difficulties, egg freezing has its benefits, such as giving women undergoing ART another option to consider. For example, cryopreserving eggs before cancer therapy can help protect a woman's fertility. Younger women without a partner who may want to delay childbearing until later—knowing that aging reduces the odds of a successful pregnancy—may also benefit.
"Cancer treatments such as chemotherapy and radiation can render a woman sterile," Daneshmand explained. "We also know that women 35 years and older have greater difficulty conceiving, but in the absence of a suitable partner may have no choice about childbearing until now."
Daneshmand and colleague Bruce Shapiro, MD, claim they've refined a process for freezing eggs that they say has been highly successful at their clinic in Las Vegas and nearby Henderson, Nevada. Nearly a dozen patients to date have used egg freezing as an option at the clinic, and two pregnancies resulted last year. They utilize a protocol that reduces the temperature of the cryoprotectant with the aim of minimizing the damage that can occur—a modification of a standard embryo-freezing protocol. "That seems to have worked," Daneshmand said.
Women interested in egg cryopreservation typically undergo an initial consultation, followed by a full medical history and thorough physical exam, which includes egg quality testing. For those interested in egg freezing, patients would then undergo an IVF cycle, which begins with standard ovulation induction using a protocol of medications and ends with egg retrieval followed by freezing of the eggs collected. But not all women may be suitable candidates. "It may not be feasible in all patients because some patients may not have very good quality eggs," said Daneshmand.
Caveat: It's Still Experimental
Despite the encouraging outcomes, Daneshmand is still only cautiously optimistic about routinely freezing eggs. "You cannot extrapolate that to mean that this is now standard therapy. Even the American Society for Reproductive Medicine [ASRM] treats egg cryopreservation as still experimental in nature, and I fully agree with them," he said. But while the success rate using frozen eggs is rather mediocre today, Daneshmand says it is improving.
In the meantime, medical researchers are continuing to work toward making improvements at egg freezing. The most rapid improvements in research will likely involve egg donation, one expert wrote, since "better quality oocytes [eggs] can be expected to be retrieved from donors, and results from oocytes may be available more rapidly since the storage period is likely to be less than that for oocytes stored for patients' own use."6
1. Kupker W, Al-Hasani S, Diedrich K. The use of cryopreserved mature and immature spermatozoa in assisted reproduction. Minerva Ginecol 2004 Jun;56(3):205-16.
2. American Foundation for Urologic Disease. Sperm Banking. Available at: http://www.afud.org/education/infertility/spermbank.asp. Accessed February 22, 2005.
3. Thomas Jefferson University Hospital. Center for Reproductive Medicine. Embryo Cryopreservation. Available at: http://www.jeffersonhospital.org/obgyn/article4518.html. Accessed March 1, 2005.
4. Smith GD, Silva E, Silva CA. Developmental consequences of cryopreservation of mammalian oocytes and embryos. Reprod Biomed Online 2004 Aug;9(2):171-8.
5. Porcu E, Fabbri R, Seracchioli R, Ciotti PM, Magrini O, Flamigni C. Birth of a healthy female after intracytoplasmic sperm injection of cryopreserved human oocytes. Fertil Steril 1997 Oct;68(4):724-6.
6. Paynter SJ. Current status of the cryopreservation of human unfertilized oocytes. Hum Reprod Update 2000 Sep-Oct;6(5):449-56.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
