**10. References**


Vitrification is a very promising cryopreservation method with many advantages, and an ever increasing clinical track record. A standardized vitrification protocol applicable to all stages of the pre-implantation embryo may not be realistic because of: **a)** different surfaceto-volume ratios; **b)** differing cooling rate requirements between oocytes, zygotes, cleavage stage embryos and blastocysts; and **c)** variable chill-sensitivity between these different developmental stages. Currently however, the most widely used protocol applied to any embryo stage is the two-step equilibration in an equi-molar combination of the cryoprotectants ethylene glycol and DMSO, at a concentration of 15% each (v/v)

For the adoption of vitrification in ART, as with all new technologies, there has been initial resistance; but as clinical data has been accrued, this technology is becoming more commonly adopted as standard procedure in many IVF programs worldwide. With this increased use in human assisted reproduction will come evolution of the vitrification process as it is fine tuned to clinical needs, so pushing forward its development to higher

The author thank the *Fertility Centers of Illinois* (FCI) and the embryologists at the FCI IVF Laboratory River North for their invaluable contributions and support in pushing vitrification to become our standard protocol for cryopreservation of human oocytes and

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human oocytes frozen with a slow freezing procedure involving high sucrose

**8. Conclusions and future directions** 

supplemented with 0.5 mol/l sucrose.

**9. Acknowledgement** 

**10. References** 

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**7** 

*USA* 

**Oocyte Cryopreservation for the Elective** 

Cryopreservation has been a technique used in reproductive endocrinology and infertility medicine since the early 1980s. Embryo cryopreservation, specifically, has been widely used in many in vitro fertilization (IVF) programs worldwide. This method has been well studied and is a common strategy employed for storing supernumerary embryos after IVF cycles, among other applications. Oocyte cryopreservation, which involves cryopreservation of unfertilized human ova, is a newer procedure that is gaining popularity due to its many benefits, including delay of childbearing, fertility preservation for cancer patients, and avoidance of ethical, religious or legal dilemmas surrounding embryo cryopreservation. While this technique is still considered "experimental," oocyte cryopreservation is rapidly gaining acceptance in the field of fertility preservation. The current chapter discusses the multifaceted reasons for delayed childbearing, the applications of oocyte cryopreservation, and technical aspects of this procedure. Additionally, arguments are presented to counter the "experimental" label of

The first human pregnancy after cryopreservation and thaw of an 8-cell embryo occurred in 1983 (Trounson & Mohr, 1983). The first reports of mature human oocyte cryopreservation also occurred in the 1980s, with the first live birth after oocyte cryopreservation using a slow-freeze method being reported in 1986 (Chen, 1986). In this early case report, mature oocytes were cryopreserved using a slow-freeze, rapid-thaw method and DMSO was used as a cryopreservant (Figure 1). Chen achieved an egg survival rate of 80%, with an 83% fertilization rate in the thawed surviving oocyte population. This cohort of 40 oocytes ultimately resulted in one viable twin gestation. Despite this promising early work, significant advances in the field of oocyte cryopreservation did not occur until decades later. Since the first reports of successful egg freezing, there have been many changes and advances in the protocols and techniques utilized to maximize post-thaw success rates. Alterations in cryopreservants and media have been tested and improved in the past three decades. Replacement of sodium with choline in the cryopreservation media has been shown to improve cryopreservation outcomes (Quintans et al., 2002; Stachecki et al., 1998). Alternative strategies, including trehalose injection have also been introduced in attempts to

improve survival of cryopreserved oocytes (Eroglu et al., 2000; Jain & Paulson, 2006).

oocyte cryopreservation and obstetric and perinatal outcome data are analyzed.

**2. The history of human oocyte cryopreservation** 

**1. Introduction** 

**Preservation of Reproductive Potential** 

Catherine Bigelow and Alan B. Copperman *Mount Sinai School of Medicine, New York, NY* 

