More on Egg & Ovarian Tissue Freezing
Chemotherapy and radiotherapy are toxic to oocytes, leaving few, if any, viable eggs.
Ovarian tissue freezing is an alternative strategy, apart from oocyte freezing. It offers women with cancer the chance to preserve their oocytes, so that they may have children in the future. Ovarian tissue will be transplanted back into the body and there are already pregnancies recorded in the literature.
Which women are suitable for oocyte freezing?
1. Those diagnosed with cancer and have not yet begun chemotherapy or radiotherapy.
2. Those undergoing IVF treatment who do not consider embryo freezing an option.
3. Those who would like to preserve their future ability to have children, either because they do not yet have a partner, or for other personal or medical reasons.
4. It is also an important choice for couples undergoing IVF who are against embryo freezing due to religious or ethical reasons. These couples can fertilize only as many oocytes as will be used in the IVF cycle and then vitrify the remaining oocytes. Thus, there are no supernumerary embryos created, and there is no need to dispose any unused embryos, a practice which can raise ethical dilemmas for certain people.
5. Oocyte freezing can also be beneficial for women who, for educational purposes, career or other reasons, desire to postpone childbearing. Freezing eggs at an early age may ensure a chance for a future pregnancy.
6. Moreover, women with a family history of premature ovarian failure may benefit from fertility preservation. With oocyte freezing, they will have a deposit of frozen eggs, in the likelihood that their eggs are depleted at an early age.
Oocyte collection for freezing is performed in the same manner as in in vitro fertilization treatment cycles. This includes almost 2 weeks of hormone injections for ovarian stimulation and multiple oocyte maturation.
When oocyte maturation is completed, ovulation induction is performed and the oocytes are collected with an ultrasound guided needle transvaginaly. The procedure is usually performed under mild sedation and the eggs are immediately frozen.
The oocyte is the largest cell in the human body and contains a great amount of water. During oocyte freezing, the formation of ice crystals can destroy the integrity of the cell. In order to prevent this, the oocyte must be dehydrated prior to freezing. This is done using cryoprotectants which replace most of the water within the cell and inhibit the formation of ice crystals.
Oocytes are frozen using either a slow-cooling method or a newer method known as vitrification. The latter method offers high success rates worldwide and has become the method of choice in many laboratories.