Barcelona, 4 July 2018: Despite dramatic uptake in the numbers of women electing to freeze their eggs as insurance against an anticipated age-related fertility decline, there is still little that clinics can predict about outcome based on real-life experience. Indeed, at one of Europe's biggest fertility centres - the Brussels Centre for Reproductive Medicine in Belgium - only 7.6% of women have returned to thaw their eggs and try for a pregnancy. And only one-third of those have been successful.

Details of the follow-up, which recorded the experience of 563 women freezing their eggs between January 2009 and November 2017, are presented as a poster here at the 34th Annual Meeting of ESHRE in Barcelona. Such details, said investigator Michel De Vos from the Brussels group, "are needed for a comprehensive appraisal of social freezing". Otherwise, he added, "little is known about these 'social freezers' and their reproductive outcomes."

The review of data showed that the 563 women in the series had 902 assisted reproduction treatments to collect eggs. And that:
* the mean age of those freezing their eggs was 36.5 years
* a mean number of 8.5 eggs per patient were collected and frozen (by the rapid freezing technique of vitrification) at each treatment cycle 
* so far, just 12.8% (72 of 563) have returned to the clinic for reproduction treatment; of these, no more than 43 had their eggs thawed, fertilised and transferred
* of these social freezers 43% had fertilisation with donor sperm either by intrauterine insemination or ICSI
* the overall survival rate of thawed eggs was 73.4%, reflecting the high efficiency of the vitrification technology
* in total the ongoing pregnancy after embryo transfer was 32.6% (14/43)

De Vos also noted that the majority of the social freezers who did return had found a suitable partner to pursue motherhood. But from the data he was unable to clarify "whether their previous decision to undergo oocyte cryopreservation has enhanced the probability of a live birth".

De Vos reported that these results in Brussels are in line with others from large fertility centres, of which one (in Valencia) recorded an ongoing pregnancy rate of 21%, and reflect the limitations of social egg freezing for women freezing eggs after the age of 35. He added that the average number of eggs retrieved in social freezers who did have an ongoing pregnancy was 9.2 eggs per patient.

While social egg freezing in Brussels reflects an upward trend in popularity apparent in many other large European and US fertility centres, De Vos urged women considering uptake after the age of 35 "not to have unrealistic expectations". "Our results show that one in three women who return to the clinic do achieve an ongoing pregnancy with their vitrified oocytes," said De Vos. "They returned at a mean age of 42 years after having their oocytes vitrified at a mean age of 36 years." But he warned that - as with any fertility treatment - egg quality declines markedly with age, and success rates will be lower than 33% in women freezing their eggs beyond this age.