An overview of oocyte cryopreservation

Abstract

The ability to cryopreserve human oocytes and store them indefinitely would be beneficial for cancer patients at risk of becoming sterile after therapy, allow women to delay reproduction, and alleviate religious concerns associated with embryo storage. In 1986, Chen was the first to report a pregnancy originating from a frozen-thawed human oocyte. Although over 100 babies have been born from oocyte storage since then, pregnancy rates remain unacceptably low. Adapting embryo cryopreservation techniques to oocyte storage has had limited success and new reproducible methods are needed. Problem areas other than intracellular ice formation and osmotic effects need to be identified. A broad approach of critical analysis should be conducted regarding the entire cryopreservation process from pre-equilibration and cooling, to thawing and stepout. All established facets deserve reanalysis in order to assess which aspects can be optimized or changed so that cellular demise can be avoided and cellular viability enhanced. New methods, including the use of choline-based media and vitrification have proven useful in increasing survival and pregnancy rates in some clinics. Other methods yet untested, such as injection of complex carbohydrates into the oocyte, deserve further studies. Vitrification research has led to the formulation of new ideas and has demonstrated the flexibility of cells to survive cryopreservation. Although successful, vitrification protocols are potentially harmful and technically challenging, due to elevated cryoprotectant concentrations and rapid cooling rates. Bovine embryo vitrification methods have been used to store human oocytes and embryos, particularly blastocysts with some success. Vitrification solutions containing high molecular weight polymers have also proved beneficial by reducing solution toxicity. In general, further advances are needed to improve human oocyte storage before widespread routine clinical use.

Human oocyte and ovarian tissue cryopreservation and its application

“…The first birth after human oocyte cryopreservation was reported in 1986 [19]. Until 2004, approximately 100 children had been born from oocyte freezing, but the pregnancy rates were very low (1% to 5%) after transfer of embryos derived from frozen oocytes [20][21][22]. There were various reasons for this limited success: low oocyte survival rates (25-40%), low fertilizations after traditional in vitro fertilization, a high incidence of polyploidy, and poor developmental ability of the embryos [19,21,23,24].…”

Vitrification of cleavage stage mouse embryos by the cryoloop procedure

“…Data indicate that vitrification is substantially better for cells with high chilling sensitivity such as mammalian embryos, human, bo vine and porcine oocytes and/or in vitro produced bovine embryos Vajta et al, 1997;Vajta, 2000;Dinnyés et al, 2000;Massip, 2001;Songassen et al, 2002;Stachecki and Cohen, 2004).…”

Fertility preservation for women with malignancies: current developments of cryopreservation

“…Cryopreservation of oocytes can be used in single women who can undergo a stimulation cycle, although the effectiveness of this technique is very low, with pregnancy and delivery rates ranging from 1 to 5% per frozen oocyte. [18][19][20] Ovarian tissue cryopreservation is the ideal option for prepubertal girls, and for women who cannot delay the start of chemotherapy. Ovarian tissue can be frozen using different categories: cortical fragments, whole ovary with its vascular pedicle or isolated follicles.…”