Cryopreservation of gametes and embryos

Oocytes

With the entry into force of Law 40/2004 cryopreservation of oocytes has replaced the freezing of embryos in laboratory practice. According to recent legislation, it is not possible to create a number of embryos greater than that strictly necessary to optimize treatment. Therefore, if a sufficient number has been obtained, it is possible to preserve by freezing supernumerary oocytes assessing first the quality and maturity of the oocytes in the laboratory. There are two methods of oocyte cryopreservation and they differ for the concentration of cryoprotectant used and for the duration of the time of freezing. These two procedures take the name of slow freezing and rapid freezing (or vitrification). In both cases the fertilization methods of the thawed oocytes is ICSI regardless of the quality of the seminal fluid. The survival of oocytes after warming reported in the literature varies between 30% and 90%. At our laboratory studies have been carried out to evaluate the effectiveness of the different methods and their degree of invasiveness on oocytes and in particular on the oocyte meiotic spindle (Larman et al., 2007). The freezing of oocytes by vitrification is considered today to be the most effective technique, and is therefore the one adopted at our center since 2008 with excellent results in terms of survival (96.5%) and embryo development (in line with that obtained with fresh oocytes). The rates of pregnancy are also very encouraging (see success rate). It should however be noted that our data and the data present in the literature lack a sufficient number of cases to draw conclusions relating to the health of the children born as a result of oocyte cryopreservation. To date there are no reports of increases in any disease. The assessment of the risk of abnormalities, malformations and neonatal pathologies is very difficult. It is reasonable to assume an incidence of chromosomal abnormalities and malformations not lower than that found in children born after ICSI.

Spermatozoa

The cryopreservation of spermatozoa is a method aimed at securing the self preservation of male gametes for those patients who must undergo radiation therapy or chemotherapy that may compromise irreversibly the production of viable sperm. This technique can also be addressed to patients who have a severe alteration in seminal fluid parameters (severe oligoasthenoteratospermia) to ensure the conservation of spermatozoa in the case of a worsening of reproductive capacity in time. This technique also allows the cryopreservation of spermatozoa obtained surgically from the testis or from the epididymis in order to avoid the patient from having to undergo surgery for each cycle of artifical insemination.

Embryos

Law 40/2004 on medically assisted fertilization does not allow the freezing of embryos except in cases where it is not possible to transfer the embryos for serious and documented health conditions of a woman not foreseeable at the time of insemination. In addition, by way of derogation from the general principle of prohibition of cryopreservation, any supernumerary embryos can be cryopreserved if their transfer is contrary either to the needs of procreation or to interest of the patient’s health (Constitutional Court Ruling No.151/2009). Any embryo that is not transferred to the uterus will be frozen at the expense of the Center pending future implantation.