Fine-tuning the process of egg freezing can improve the odds of achieving a successful pregnancy afterwards, say doctors at the University of Southern California. Their findings were unveiled at a meeting of fertility experts in Montreal last month.1
Unique Approach Used
The researchers examined the outcomes after using a specific egg-freezing protocol that involves the use of slow freezing and fast thawing, as well as special culture medium in which the eggs are stored. The culture medium includes the use of choline (KOH-leen), a substance that helps stabilize the egg's surrounding membrane during the freezing process, explained study leader John Jain, MD, an associate professor of Reproductive Endocrinology at USC.
"To my knowledge, this is the first with both the type of culture media and study design," Jain explained, in an interview.
An Option in Cancer Therapy
Egg freezing has become an attractive option for women who wish to preserve their fertility after undergoing cancer treatment that can be potentially harmful to women's reproductive organs, experts point out. But it has had its challenges, including low pregnancy odds compared to sperm banking, for example. Additionally, women undergoing cancer treatment don't always have the time needed to undergo ovulation induction prior to receiving their cancer treatment, experts say. Nonetheless, in recent years, medical researchers have been working steadily to improve the odds of success using egg freezing.2
One of the reasons pregnancy is not easily achievable after egg freezing is due to the fact that the egg can be easily damaged by ice crystals during the freezing or thawing process. In addition, hardening of the egg's outer shell after freezing makes it more difficult for sperm to penetrate the egg for fertilization.3
Comparable Pregnancy Outcomes Achieved
In this study, Jain and his colleagues at USC's Keck School of Medicine evaluated the pregnancy outcomes of ten women who underwent egg freezing. Each woman underwent controlled ovarian hyperstimulation (COH) to induce ovulation using a protocol of fertility drugs.
After eggs were collected, they were frozen using a unique slow-freeze, rapid-thaw approach in a culture medium that included choline. So far, the researchers have frozen and thawed nearly 100 eggs from eight women who had tubal factor infertility. Of those, nearly 60 eggs survived the freezing process, and 38 of those were fertilized. Eight of 29 resulting embryos that were transferred successfully implanted in uteri, and five pregnancies were achieved. That translates to a 62% success rate per patient.
The 28% implantation rate reported in this study is "in the same range as those of fresh or cryopreserved [frozen] embryos," wrote Jain and his colleagues. This "results in a reasonable chance of subsequent pregnancy," they added.
Jain pointed out that the while trial is still continuing, he and his associates have been able to maintain comparable results going forward.
Not only the use of the specially-prepared culture medium, but also "our laboratory expertise and using the full cohort of eggs (up to 13 eggs) derived from a single IVF cycle for each subject" contributed to the success rate in this study, Jain said.
Still Investigational
Despite these promising results, Jain stresses that egg freezing should still be performed under research protocols, and patients should be informed that the technique is still considered experimental.
One hurdle that first needs to be cleared before the technique can be used in standard clinical practice is "support by the ASRM [American Society for Reproductive Medicine]," he said. "I believe they want to see consistent and repeatable results at multiple clinics before they endorse it for clinical practice. Prior to the endorsement of the ASRM, individual clinics will offer [egg freezing] services based on their own experience and results," Jain added.
Still, he says, the approach is a promising one for women whose reproductive organs can potentially be damaged by radiation or chemotherapy for cancer. Older women who want to delay their goal of becoming mothers could also potentially benefit from egg freezing, Jain stressed.
The results of his study, so far, help support that view, he said. "We have no miscarriages, and all pregnancies are into the second or third trimester, or have delivered (two delivered so far). We also have a triplet pregnancy. This points to a robustness in the technology that is reassuring."
1. Jain JK, Francis MM, Bayrak A, Quinn P, Paulson RJ. Pregnancy outcome after cryopreservation of all oocytes from a single ovulatory cohort: a prospective clinical trial. Conjoint Meeting of the American Society for Reproductive Medicine 61st Annual Meeting and the Canadian Fertility and Andrology Society 51st Annual Meeting. 2005 Oct 15-19. Montreal, Quebec, Canada.
2. Practice Committee of the American Society for Reproductive Medicine. Ovarian tissue and oocyte cryopreservation. Fertil Steril 2004 Oct;82(4):993-8.
3. Matson PL, Graefling J, Junk SM, Yovich JL, Edirisinghe WR. Cryopreservation of oocytes and embryos: use of a mouse model to investigate effects upon zona hardness and formulate treatment strategies in an in-vitro fertilization program. Hum Reprod 1997 Jul;12(7):1550-3.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
