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Egg Freezing and Ovarian Tissue Cryopreservation are Safe for Offspring and Offer Advantages for Patients


17 October 2007

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Washington, DC- Freezing eggs or ovarian tissue offers advantages to women undergoing ART who have extra eggs but prefer not to create and freeze extra embryos and to women at risk of losing ovarian function as a consequence of treatment for cancer. Today, at the 63rd Annual Meeting of the American Society for Reproductive Medicine, researchers presented new experimental data on the safety and success of different techniques for oocyte and ovarian tissue cryopreservation. 

In a prospective, randomized clinical study, Dr. Gary Daniel Smith and his colleagues found that eggs frozen quickly using the vitrification (V) technique survive freezing and thawing better than eggs frozen using a slow-rate freezing (SR-F) technique. In addition, embryo development and clinical pregnancy rates were better with vitrified eggs than with slow frozen eggs. Couples going through IVF and having more than 9 eggs retrieved were given the opportunity to freeze their extra eggs which were randomly assigned to V or SR-F. If the fresh IVF cycle did not result in a pregnancy, the couples could return to use their cryopreserved eggs for a later attempt at pregnancy. Eggs were frozen in 165 cases; in 63 of these cases, patients chose to use their frozen eggs. Vitrified/warmed eggs survived at a rate of 73% compared with slow frozen/thawed eggs at 66%. Fertilization was accomplished through ICSI. Although the number of embryos transferred between the two groups was similar, clinical pregnancy rates were higher for V eggs versus SR-F eggs (34% vs. 18%). The number of frozen eggs required to establish a clinical pregnancy was 21 vitrified/warmed eggs versus 45 slow-rate frozen/thawed eggs.

In order to determine whether egg freezing has any detrimental effects on the babies born from embryos created with frozen eggs, researchers in Bologna, Italy collected data on 105 babies conceived with eggs that had been frozen using a slow-freezing, rapid thawing technique. Of the 149 pregnancies they observed, 89 resulted in the births of 105 babies. Fifty-nine of the deliveries were by cesarean section. Average gestation was normal- 38.9 weeks, and the babies’ average weights were normal– 3.35 kg for singletons and 2.6 kg for twins. Thirty-five of the pregnancies resulted in miscarriage and one pregnancy was aborted because the fetus had a trisomy 21. Twenty-three pregnancies were on-going. Of the 105 babies born, two had malformations; the researchers noted that their fathers had suffered from severe male factor infertility. 

Additional reassuring data on the development of children conceived with frozen eggs comes from Dr. Ilan Tur-Kaspa and his colleagues in Chicago. Their retrospective study surveyed the literature on oocyte cryopreservation and found 272 clinical pregnancies from embryos created with frozen eggs up to July 2006. The results of genetic testing were, for the most part, normal with 93.8% normal results for eggs that had PGD of the second polar body and karyotyping after fertilization. The 272 clinical pregnancies resulted in 51 miscarriages, 2 tubal pregnancies, 156 deliveries of 197 babies and 63 ongoing pregnancies. Health status at birth was reported for 69.5% of the babies and of those, 99.3% were healthy. Follow-ups at six months to three years were reported for 31% of the children and all continue to develop normally. Only one twin was born with a congenital anomaly.

Ovarian cryopreservation has been used for a decade at the Weill Medical College of Cornell University to preserve the possibility of fertility for women being treated for many different cancers. To obtain a perspective on the long-term storage and use of banked ovarian tissue, 55 who had undergone ovarian tissue cryopreservation between May 1997 and March 2007 were surveyed by telephone. Fifty women responded. The patients were treated for a variety of different conditions and were an average of 28 years old when their ovarian tissue was frozen. The patients ranged in age from 4 to 44 (average = 28 years old) at the time of ovarian tissue cryopreservation and were treated for a variety of different conditions. All of them had at least one ovary removed and 73% stopped menstruating regularly after their treatment. At the time of the survey, the average time their tissue was in storage was four years and only three had undergone transplantation. Of the three, one had her tissue transplanted back to the location of her ovary and two had their tissue transplanted elsewhere- one of these two failed to become pregnant after an embryo transfer; the other became pregnant twice spontaneously, losing one pregnancy and then giving birth to a healthy child. 

“These data will be reassuring to patients who need to freeze eggs or ovarian tissue to preserve their fertility,” Steven J. Ory, MD, President of the American Society for Reproductive Medicine remarked. “Although more frozen eggs are required to establish a pregnancy than fresh eggs, frozen eggs that fertilize, develop into viable embryos and implant are as likely to result in healthy children as fresh eggs.” 

O-35, Fioravanti et al, Prospective randomized comparison of human oocyte freezing and vitrification: an update.

O-36, Borini et al, Survey of 105 babies born after slow-cooling oocyte cryopreservation.

O-37, Tur-Kaspa et al, Genetics and health of children born from cryopreserved oocytes.

O-33, Elasser et al, (A. Elasser, O. Oktem, K. Oktay,) Fertility preservation with ovarian cryopreservation: a decade of experience.

The American Society for Reproductive Medicine, founded in 1944, is an organization of more than 8,000 physicians, researchers, nurses, technicians, and other professionals dedicated to advancing knowledge and expertise in reproductive biology. Affiliated societies include the Society for Assisted Reproductive Technology, The Society for Male Reproduction and Urology, the Society for Reproductive Endocrinology and Infertility, and the Society of Reproductive Surgeons. 

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Date Added: 17 October 2007   Date Updated: 17 October 2007
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