"In my opinion, the most important alteration found in frozen-thawed oocytes could be the presence of vacuolisation. This is a quite non-specific feature commonly found in cells that are responding to an injury and, even in absence of other alterations, might lead to an impairment of the developmental potential of the frozen-thawed oocytes.
"As far as the other possible alterations are concerned, the reduction in amount and density of the cortical granules and the consequent hardening of the zona pellucida in frozen-thawed oocytes may be an expected phenomenon that possibly could be by-passed by the application of ICSI technique at insemination; other zona pellucida damage may greatly affect oocyte survival but it depends on the type and amount of the damage; alterations in the mitochondrial organisation can be very subtle and deserve to be further investigated by transmission electron microscopy."
Professor Arne Sunde, former chairman of ESHRE, said: "Cryopreservation of human semen and embryos has been a routine procedure since the early 1980s, while cryopreservation of mature oocytes has proved to be very difficult. Current techniques for freezing oocytes have a very low success rates in terms of viable pregnancies per frozen oocyte. This is probably due to basic biological differences between oocytes and sperm cells and embryos.
"For decades men have had the opportunity to freeze sperm prior to treatment for malignant diseases, and thousand of babies have been born to couples where the male is an infertile survivor of cancer treatment. With the current techniques, women would need to freeze hundreds of oocytes in order to have a reasonable chance of obtaining a child, but by using the technique of Dr Kuwayama and his colleagues, it will be possible
Source:European Society for Human Reproduction and Embryology