Egg and Embryo Freezing
Fertility Preservation & Egg and Embryo Freezing
For women who are not ready to start their family at the present moment, oocyte cryopreservation, or egg freezing, is an option. Some women may wish to preserve their fertility if they are about to undergo cancer treatments that may decrease their future fertility potential, while others choose to freeze eggs if they are not in a relationship and/or are not ready to have children, but want to have the option to use eggs from their current young age if they have problems conceiving in the future.
The two most common methods of fertility preservation for females are embryo freezing and egg freezing. Embryo freezing is well established and increasingly there is data to that suggest that egg freezing is improving as a technique and it is an option we can offer patients who are not inclined to freeze embryos. In recent literature, several studies have reported better post-thaw egg survival, fertilization, and pregnancy rates with egg freezing compared to past research and, for this reason, a renewed interest in egg freezing has occurred.
The process of freezing the eggs is identical to an in vitro fertilization (IVF) cycle up through the egg retrieval process. In summary, with the patient administering injections to stimulate the ovaries to grow follicles, the follicles and hormone levels are closely monitored with ultrasounds and blood work. Once the follicles are ready and mature, the egg retrieval is performed. This is done under anesthesia and the eggs are then frozen.
There are two methods used to freeze eggs, the slow-freeze method and a faster method called vitrification. It is with the latter that we have seen better pregnancy rates and therefore this is the method that we use. The eggs remain frozen until a pregnancy is desired, at which time the eggs are removed from the liquid nitrogen and warmed.
If embryo freezing is desired, then this can be done with a partner or donor sperm. Again, the procedure is equivalent to a general IVF procedure. The egg and sperm are allowed to fertilize by mixing (conventional fertilization) or undergo intracytoplasmic sperm injection (ICSI). The fertilized eggs result in embryos and these are allowed to develop in incubators and subsequently frozen at the appropriate time.
Over the past few years, there have been a number of randomized controlled trials demonstrating that using frozen eggs is equivalent to using fresh eggs when comparing pregnancy rates and/or live birth rates. Most of this data is in women who are under age 38. Despite that frozen eggs are having pregnancy success rates similar to fresh eggs in some studies, there remain a limited number of established pregnancies and deliveries derived from frozen eggs compared to frozen embryos.
In the small number of studies that have been performed looking at babies derived from frozen eggs, there have been no increases observed in the number of abnormal or stray chromosomes. One follow-up of 13 children resulting from frozen eggs failed to reveal any abnormalities in the chromosomal composition, mean age at delivery, mean birth weight, or organ formation. In another 3-year follow-up study of 16 children born post egg freezing, one case of a heart defect was noted but there was no evidence of any intellectual or developmental deficits in any of the children.