Intentionally delaying motherhood: oocyte vitrification
Although egg cryopreservation was introduced more than 20 years ago, the results so far have been dispiriting, but in recent times there have been remarkable advances and improvements in the field of cryobiology which have made its acceptance as a routine technique possible.
Faced with the conventional protocol of cryopreservation, that is slow freezing-rapid thawing, in recent years a more effective freezing technique has been introduced called vitrification which is both simple and economical.
Vitrification is a cryopreservation procedure characterised by a high concentration of cryoprotectants and a high cooling rate, which prevents the formation of intracellular ice crystals. In the field of assisted reproduction the first full-term pregnancies and births after vitrification of human eggs were obtained in 1999 and 2000 (Kuleshova et al., 1999, Chen et al., 1999, Yoon et al., 2000).
Cryopreservation techniques can effectively offer women with no fertility problems today, the possibility of undergoing assisted reproduction techniques in the future with their own eggs. For example, women who are diagnosed with cancer and must undergo therapy which have gonadotoxic effects that lead to loss of ovarian function and early menopause would preserve their fertility through the vitrification of their own eggs prior to treatment. Although each year the incidence of cancer increases, mortality has been reduced due to advances in early diagnosis and treatment. Motherhood is a major concern for these women of childbearing age who survive the disease, and the freezing of eggs would give them the opportunity to fulfill their dream of becoming a parent.
In today’s society there is a trend towards postponing parenthood until later in life, mainly due to socio-economic reasons. This has resulted in most of these women having trouble conceiving in the future due to the decreased fertility associated with age. Egg cryopreservation would provide the opportunity for these women to preserve their eggs until they are ready to be parents once they have attained professional and financial stability.
Oocyte vitrification is also an alternative in countries where embryo freezing is not legal as well as for those couples who for ethical reasons do not want to freeze their embryos. It would also avoid the issues surrounding frozen embryo custody in the case of separation or divorce.
Egg cryopreservation would also enable the creation of donor egg banks. There are many complications relating to the donation of fresh eggs, among which include the availability of suitable donors and the need to synchronise the recipient and donor cycles. The vitrification of donor eggs avoids these problems and actually facilitates the process.
Finally, it also represents an alternative in cases where the man finds it impossible to give a semen sample on the day of ovarian puncture, or when it is necessary to delay the time of embryo transfer, for example, in cases where there is a risk of ovarian hyperstimulation syndrome.
In conclusion, cryopreservation of human eggs is a technique with significant clinical applications for assisted reproduction laboratories and the progress made in these techniques have resulted in a clear benefit for patients.
Jaime Guerrero, biologist of Instituto Bernabeu.
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