The human egg is the largest cell in the body. The cell has high water content, a special membrane surrounding it that is less permeable than other cells, and the chromosomes are spread on a structure called the spindle rather than enclosed within the nucleus.
When beginning the egg freezing process, the patient will take a medication that will help to stimulate the ovaries to increase the number of eggs produced. Your fertility specialist will monitor your response and modify medications as needed. After a few days of stimulation, you will come to the office and your eggs will be retrieved using a vaginal ultrasound and needle aspiration while under sedation. Most women can usually return to work the day of or the day following the procedure.
After retrieval, your eggs will then be frozen using one of two methods:
- Rapid freezing (vitrification): Rapid freezing is performed four hours after retrieval; the temperature of the eggs is lowered very quickly by using high concentrations of cryoprotectant materials in order to avoid damage to the egg. Eggs are placed in a small volume of solution and then transferred to a special device (cryotip, cryotop, cryoloop or cryoleaf). The device is sealed and then plunged into liquid nitrogen. We use the cryotop egg vitrification method at NYC IVF; eggs survive thawing better than slow freezing (>90% survival), which has shown to produce the best outcome. At NYCIVF we use the vitrification method with 95-97% thaw survival rate. Frozen eggs can be stored for a very long time and can be transferred in liquid nitrogen to a long term storage facility.
- Slow freezing (older modality): The egg is placed within a solution that prevents ice damage (cryoprotectant) and the temperature is lowered slowly.
When you are ready to use your eggs, the lining of your uterus will be prepared, your eggs will then be thawed, fertilized through ICSI (injection of one sperm into each egg), and then transferred to the uterus. In this process, partner or donor sperm can be used. You will not require injections or anesthesia, only monitoring of the lining of the uterus using ultrasound. Approximately one or two embryos are transferred based at your age at time of egg freeze. Using vitrification, the majority of the eggs usually survive the thaw and about 85% fertilize with ICSI. You can also opt to proceed to PGT and freeze all resulting embryos.
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