State of the art of slow freezing and vitrification of immature, mature Oocytes and embryonic stages

Currently the success through natural fertilization has decreased in humans and domestic species worldwide. In Mexico, subfertility problems have come to affect 1 of 6 couples. According to the World Health Organization, the main causes are: endometriosis (42%), ovulatory disorders (33%), and the increase in the diagnosis of obesity, diabetes and cancer. On the other hand, domestic species of economic importance such as pigs, sheep and cattle have reported numerous fertility problems whose main causes are: 1) low sperm quality due to excessive ejaculations, 2) nutritional deficit, 3) infections, 4) endometriosis, 5) reduced food sources, and 6) heterozygosity loss. Therefore, oocyte and embryo cryopreservation represents an important tool for fertility preservation in the development of assisted reproductive technologies (ART). ART refers to those treatments that can solve natural fertilization problems improving human reproduction and animal production. The importance of cryopreservation is based on its application in patients with ovarian hyper stimulation syndrome diagnosis, cancer, and maternity at advanced age (>40 yr.), for the creation of gene banks and generation of a genetic reservoir in endangered species, such as the Mexican hairless pig and bighorn sheep and finally for basic and applied research. The aim of this review was to analyze two types of cryopreservation methods, slow freezing and vitrification, in terms of its success and impact on different developmental stages.