Comments on oocyte cryopreservation.

Recently, Robert Winston stated publicly that freezing human oocytes could cause irreparable harm to future generations. In this paper, this affirmation is refuted with arguments and facts. With regard to the low efficacy of the oocyte freezing technique, data are provided on the number of frozen oocytes required to achieve one pregnancy: 100, 17 and 25 in three different papers, compared with 50 fresh oocytes in another. Two recent articles are cited. One shows similar results (pregnancy/cycle) when using frozen oocytes and frozen embryos (17.2 and 18.7% respectively). The other reported birth rates with fresh oocytes (57.9%), frozen embryos (52.9%) and frozen oocytes (45.8%). The legal situation with regard to freezing oocytes in Spain is described, as is the legal uncertainty experienced by the CEFER Reproduction Institute when it began freezing human oocytes for use in assisted reproduction.