Introduction
Over the last several decades, much effort has been extended towards the successful cryopreservation (freezing) of human cells and tissues. Cryopreservation of human sperm has been available for decades enabling men to bank sperm who otherwise may become sterile, due to radiation, chemotherapy, or surgical castration. Scientists have been trying to cryopreserve human eggs for all of the same reasons. In addition, because there is no ongoing production of eggs throughout a woman’s life, the quality of eggs released each month deteriorates with age, making childbearing after age 35 more difficult and risky. Technically, cryopreservation of sperm is quite simple due to the small size and relatively low water content of spermatozoa. The egg is a large cell with high water content, and is therefore prone to ice crystal damage. It is the prevention of this ice crystal formation that is critical to successfully freezing an egg.
Since 1984 advanced reproductive medicine programs worldwide have been cryopreserving fertilized eggs, i.e. (pre) embryos. Thousands of babies have been born using this technology with a large body of reassuring health data. As opposed to the cryopreservation of an unfertilized egg, most of the critical functions of the cell have already been performed when freezing (pre) embryos. Therefore, if a female desirous of cryopreservation of her gametes has a stable male partner, it is recommended in most cases to cryopreserve (pre) embryos.
At the Florida Institute for Reproductive Medicine we have had 56 babies born to date. Given the number of eggs frozen and thawed to produce these pregnancies, we believe this is one of the most efficient experiences with this technology in the world.
If you are considering cryopreservation of your eggs, it is of primary importance to ask some key questions:
Who may benefit from Egg Cryopreservation?
NBC Today Show - First baby born to a cancer patient after cryopreservation of eggs
Assessing Who is a Good Candidate for Egg Cryopreservation - Tests of Ovarian Reserve
Given the efficiency of our egg cryopreservation protocol, we wish to identify those individuals who are likely to benefit from this technology. For a patient 35 years old or less, on average, 12 mature eggs will be required to obtain a 50% chance of a live birth. For patients 36-38 years of age, 16 will be required. Because egg quality will vary from individual to individual, it is not possible to assert for any particular individual their chances for a successful pregnancy from a given number of eggs. Some low response individuals may need to go through more than one stimulation/retrieval cycle to obtain sufficient numbers of eggs. Some cancer or surgery patients may not be able to go through a subsequent cycle because of health or time constraints. Age is an indicator of ovarian reserve and remaining egg quality to some degree. Clearly the majority of 38 year-olds will obtain significantly fewer eggs following stimulation than the majority of 20 year-olds, but amongst all 38 year-olds there will be considerable variability. More accurate assessment of ovarian reserve can be obtained through hormonal testing. The tests that we currently recommend are the anti-mullerian hormone test, the clomiphene citrate challenge test, and follicle stimulating hormone/estradiol test. Egg quality is primarily a function of age, but does relate to ovarian reserve. Egg quality in general declines with age, and significantly so after age 37. Because of concerns over egg quality, we do not offer egg cryopreservation to patients older than 38.
