Egg Freezing: A Look at Outcome Data

An increasing number of women are postponing family building for a variety of reasons to include establishing careers, not having the right partner, not being ready to start a family as a single parent or health concerns to include the need to undergo chemotherapy and/or radiation therapy.  In the last case, freezing eggs prior to the treatment is essential for keeping open the possibility of having a child later in life.

To counteract the negative effect of age on egg quality many women are choosing the option of fertility preservation through elective egg freezing. Most of the time egg freezing is done at a center which does not have or openly provide outcome data such as the number of live births later produced with these eggs. As this is an emerging sector in the field of reproductive endocrinology, this is often due to the lack of sufficient outcome data. This dynamic may even apply to fertility clinics which specialize exclusively in egg freezing. 

This may lead to a kind of blind trust in the minimal reassurance that such a center has "excellent vitrification technique" (i.e. egg freezing) without actually giving numbers on live births. 

In a recent commentary by Tannus et. al published in the Journal of Assisted Reproduction (Volume 35, Pages 1157 – 1158) the authors caution against blind trust in a clinic’s claim of proficiency of freezing eggs. They give the following example: a 36-year old woman had her eggs frozen three times by three different embryologists. All oocytes (eggs) were thawed out on the same day by one embryologist. The oocytes frozen by two senior embryologists had oocyte survival rates of 71.4 % (10 out of 12 eggs) and 70.5% (12 out of 17 eggs), whereas the eggs frozen by a junior embryologist had a survival rate of 16.7% (2 out of 12 eggs). In this scenario, "survival rate" means the eggs were intact and viable for creating embryos.

High quality outcome data on egg thawing and take home baby rate are scarce. In a recent retrospective analysis, the outcome results from 641 women who did elective egg freezing and returned to attempt pregnancy were presented in a scientific journal (Cobo et al. Human Reproduction, Volume 33: Pages 2222 – 2231, 2018).  This is the group which had shown convincingly in 2008 that using fresh or frozen oocytes in a donor egg recipient program have comparable pregnancy outcome (Cobo et al. , Fertil Steril Volume 89: Pages 1657 – 1664, 2008). 

The more recent study showed that cumulative live birth rates were higher in elective egg freezing patients who were younger than 36 years than in patients older than 35 years. In the younger group, 68.8% out of a group of 123 patients had live births versus 25.5 % out of a group of 518 in the older group of patients. 

In this study, the authors also calculated that the chances of achieving a live birth increased dramatically by having  larger numbers of frozen eggs to work from; however, there was still a dramatic decline in the success rate in the older patient group.  The data show that the estimated cumulative rate of having a baby as follows:  the rate of success in the younger group increases from 30% with 8 frozen oocytes to 45% with 10, to 70% with 15 frozen oocytes and most dramatically to 95% with 25 frozen oocytes.  By contrast, women who were older than 35 years can expect a maximum success rate of about 50% even with a very high number of frozen eggs.

Recommendations based on the above findings for women who want to electively freeze their oocytes for fertility preservation include freezing eggs at the youngest age possible but preferably at no older than 35 years; and equally important, be certain that a minimum of 15 eggs are frozen to ensure there are enough viable eggs for creating a live baby at a later date. Keeping all of this in mind, it would be important to discuss these issues at the fertility clinic one is considering for elective egg freezing and inquiring about their own success rates and their guidelines for ensuring the best outcome possible.