Freezing eggs, a.k.a. oocyte cryopreservation, is now an option for women who desire to preserve their fertility. Women may wish to preserve their fertility if they are going to undergo cancer treatments that may decrease their future fertility potential and others choose to freeze eggs if they are not in a relationship, 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. As of the past couple of years, there is more data that suggest that egg freezing is improving as a technique and is an option we can offer patients who are not inclined to freeze embryos. In the more 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 involves the patient administering injections in order to mature more eggs than in a natural cycle, frequent monitoring in a fertility clinic using ultrasounds and blood work, a procedure to harvest the eggs, and the actual procedure to freeze the eggs itself. 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.
Over the past couple of 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 frozen eggs having pregnancy success rates similar to fresh eggs in some studies, there remains a limited number of established pregnancies and deliveries derived from frozen eggs compared to frozen embryos. This is the main reason why egg freezing is still considered experimental by the American Society of Reproductive Medicine when done for elective reasons and should be performed under the auspices of an investigational protocol.
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.
Without a doubt egg freezing is a novel and fantastic technology that is now available to preserve a woman’s fertility. With time, the goal will be to create registries to follow all of the outcomes in babies that resulted from a frozen egg in order to give us more insight to the safety of the procedure.