Efficiency of equilibrium cooling and vitrification procedures for the cryopreservation of ovarian tissue: comparative analysis between human and animal models.

OBJECTIVE: To compare the efficiency of equilibrium cooling and vitrification for cryopreservation of human ovarian tissue and to determine the best experimental model for developing new protocols.
DESIGN: Experimental prospective study.
SETTING: An academic research environment. PATIENT(S) AND ANIMAL(S): Human ovarian biopsy specimens were obtained from three women undergoing operative laparoscopy for ovarian cyst enucleation. Adult cow and pig ovaries, collected at the abattoir. INTERVENTION(S): Ovarian tissue fragments of three individuals for each species were cryopreserved by using two protocols, either for equilibrium cooling or vitrification. MAIN OUTCOME MEASURE(S): Comparison between fresh and cryopreserved tissue of primordial, primary, and secondary follicle morphology, graded in three classes. RESULT(S): Human and bovine follicles responded in the same way to the two equilibrium cooling protocols, whereas pig tissue was more cryoresistant. Both vitrification protocols caused extensive damage to the tissue of all species. Human tissue showed a response to vitrification that was different from that of both animal species. CONCLUSION(S): Bovine is a good animal model for the development of human ovarian tissue cryopreservation protocols by equilibrium cooling procedures. Vitrification is less efficient than equilibrium cooling, and at present, neither bovine nor pig can be considered relevant animal models for human tissue.