ABSTRACT
The low temperature storage of mammalian oocytes at all stages of development was pioneered in the mouse. Sherman and Lin (1,2) began to investigate the effects of cooling and exposure to cryoprotectants on mouse metaphase II oocytes half a century ago. At about the same time, the viability of immature oocytes frozen in ovarian tissue was demonstrated by the birth of live young after the tissue was transplanted (3). Interest in oocyte cryopreservation waned but was reignited when mouse embryos were frozen in 1972 (4,5). In 1976, Parkening et al. (6) reported the birth of three offspring from metaphase II oocytes frozen and held at –75°C before warming, fertilization in vitro, and transfer to surrogate mothers. Just a year later, the possibility of prolonged oocyte storage became a reality when Whittingham (7) obtained live births from frozen oocytes that had been stored at –196°C in liquid nitrogen. Mature oocytes were vitrifi ed for the fi rst time in 1988 (8). Isolated immature oocytes (9) and immature oocytes contained within isolated ovarian follicles (10,11) were frozen successfully in the 1990s.
