“Freezing time” – Fertility preservation through oocyte and embryo freezing
Cryopreservation is an extremely useful technique of assisted reproduction, as it gives the opportunity to preserve cell viability for a very long period of time – theoretically forever – in liquid nitrogen at a temperature of -196 ο C, in order to be used in the future, essentially “freezing time”. In humans, this method was first used for the cryopreservation of spermatozoa – the first use of frozen/thawed human spermatozoa to achieve a pregnancy was done in 1953 – with very good results.
The birth in 1983 of the first two children from frozen/thawed embryo transfer, was an important development in in vitro fertilization, as it gave the opportunity to reduce the number of embryos transferred, while the supernumerary embryos could be frozen for future use. Cryopreserved embryos can be used if the fresh embryo transfer failed to produce a pregnancy or in couples with a successful pregnancy who later wish to have another child. Also, in women at high risk for the development of the ovarian hyperstimulation syndrome, all embryos can be frozen and embryo transfer is deferred to a subsequent cycle; recent studies have shown that, using this approach, the live birth rate is at least as good and probably higher, without any risk for the woman. The same approach can be used when the endometrial development is not optimal or when there are factors reducing the chances of embryo implantation and pregnancy, such as premature progesterone elevation.
Until recently, oocyte cryopreservation using the older techniques was not very successful. Nevertheless, the new method of ultra-rapid freezing, vitrification, was shown to be associated with excellent results in oocyte and embryo survival rates after thawing reaching 90% but also in pregnancy rates. This development made oocyte cryopreservation a viable option for fertility preservation.
This approach is utilized in women with cancer who wish, before undergoing chemo/radiotherapy, to freeze their oocytes in order to use them, after they are cured from their primary disease, to achieve a pregnancy. This approach is already been used since many years in men with similar problems, by freezing their sperm.
Oocyte cryopreservation is also offering women, who are not ready to have children, the opportunity to store their oocytes for future use. Studies have shown that the most important factor affecting woman’s fertility is her age; the optimal reproductive age for women is 20 to 30 years, when the highest fertility rates are observed, declining thereafter due to a progressive decrease in the number and quality of oocytes. However, in Greece, as in most western societies, the age at which women have their first child has been deferred by 10 to 15 years, approximately to the age of 35, with negative impact on their fertility. Thus, oocyte cryopreservation together with oral contraceptive pills, both promote the reproductive autonomy of women: the first by giving them the opportunity to defer the age of childbearing without negative consequences and the latter by allowing them to program the time of childbearing.
In conclusion, embryo cryopreservation represents an integral part of in vitro fertilization, as it increases the efficiency and safety of the procedure, while oocyte cryopreservation allows women to preserve their fertility for medical or social reasons.