Cryopreservation

After embryo replacement, supernumerary good and high quality embryos, can be vitrified and stored in liquid/ vapor nitrogen for future use in cryocycles. If pregnancy is not achieved in the fresh cycle, or if the couple decides to have a second child, these frozen embryos are thawed on the transfer morning and replaced in the uterus, which has to be primed for a pregnancy (the intrauterine layer or endometrium has to be thick enough and receptive). Hormonal replacement therapy is completely unnecessary as oocyte pick-up is meaningless. Embryo vitrification can also be done because of clinical indications: thin endometrium, high risk of ovarian hyper stimulation syndrome (OHSS), which occurs occasionally when the patient “overreact” to the hormonal drugs given during the cycle.

Embryos can be vitrified in every step of their development from the very 1st day to the 6th day. On the contrary to the slow-freezing method, vitrification yields very high cooling rates (2000-20000 oC/ minute) with a decreased risk of cryoinjury caused by the cryoprotectants used in high concentrations. One of the most important criteria that prove the success of the vitrification method is the post-thaw survival rate, which is around 95-100% in our center. In addition to the high survival rate, vitrification is also the most successful freezing method in terms of pregnancy rates.

Although embryos can be stored for much longer times technically, regulations issued by the Turkish Ministry of Health restrict this period to 5 years. Also, according to this directive embryo freezing and thawing can only be performed with a written consent of both spouses, meaning that in case of divorce, death of a partner embryos are discarded.

Embryo vitrification
Embryo thawing

 

Freezing the embryos in nitrogen (-196°C) 
And storing them in nitrogen tanks

Ovarian tissue freezing: fertility preservation in cancer patients

Surgical, medical, and technological advances in cancer treatments have allowed improvement in the life quality of cancer patients with increased survival rates, making preservation of reproductive function a more important priority than ever before. Fertility preservation aims to maintain the fertility potential in adults or children who are at risk of sterility due to gonadotoxic anti-cancer treatment. The options of fertility preservation will depend on the age of the patients at the time of diagnosis and treatment, cancer type, severity and location, and type of treatment regimen. Although current therapy modalities, including conservative surgery, chemotherapy, radiotherapy, and bone marrow transplantation, can offer increased cure rates, aggressive chemotherapy and radiotherapy protocols affect progressively, but mostly irreversibly, the ovaries causing permanent amenorrhea and infertility. Especially, alkylating agents and ionizing radiation can damage the pool of primordial follicles, often inducing premature ovarian failure or early menopause. Thus, fertility preservation should be consistently considered for prepubertal girls and for women of child-bearing age undergoing potentially gonadotoxic treatment.

Different methods may be proposed to preserve fertility in women diagnosed with cancer. Embryo cryopreservation is very well established and available for women with a male partner, oocyte cryopreservation via vitrification provides also a useful option for fertility preservation in young women who do not have a partner.

Cryopreservation of ovarian tissue can be a valuable option when an urgent initiation of cancer treatment is recommended, leaving no time for ovarian stimulation, or for prepubertal girls, in whom the gynecologist has no other option for fertility preservation. Briefly, tissue stripes of 10x1x1 mm are prepared from the sample taken from the ovary. One strip is used for both routine pathologic/histologic evaluation and for viability staining in order to determine the basal cell/follicle count. Ovarian cortex (outer layer), comprising the follicles is detached from the stroma (inner layer) to increase the post-thaw survival rate. Samples are stored within cryoprotectants in liquid/ vapor nitrogen at -1960C until transplantation.

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