Planned egg freezing over 15 years: return to treatment and success rates in Australia and New Zealand

Abstract STUDY QUESTION What are the characteristics and treatment outcomes of women who undertook planned egg freezing (PEF) in Australia and New Zealand between 2009 and 2023? SUMMARY ANSWER There has been an average year-on-year increase in the uptake of PEF of 35%, with most women undergoing a single PEF procedure in their mid-thirties and given 10 years follow-up, a little over one in four women return to thaw their eggs, with nearly half of those using donor sperm and one-third achieving a live birth. WHAT IS KNOWN ALREADY PEF, where women freeze their eggs as a strategy to preserve fertility, has increased dramatically in high-income countries in the last decade. Despite the rapid uptake of PEF, there remains limited information to guide women, clinicians, and policy-makers regarding the characteristics of women undertaking this procedure and treatment outcomes. STUDY DESIGN, SIZE, DURATION A retrospective population-based cohort study of all women who undertook PEF in Australia and New Zealand between 2009 and 2023, including their subsequent return to thaw their eggs and treatment outcomes. Where women returned to utilize their eggs, all subsequent embryo transfer procedures were linked enabling calculation of live birth rates per woman. PARTICIPANTS/MATERIALS, SETTING, METHODS Twenty thousand two hundred and nine women who undertook PEF in Australia and New Zealand between 2009 and 2023 including 1657 women who returned to thaw their eggs. Descriptive statistics were used to characterize the cohort at freeze and thaw, along with trends in PEF. Associations between the chance of a live birth upon egg thaw and patient and treatment characteristics were evaluated using a multivariable generalized additive model. MAIN RESULTS AND THE ROLE OF CHANCE There has been a huge increase in uptake of PEF, from 55 women in 2009 to 4919 in 2023. Women who freeze their eggs are typically aged 34–38 years (interquartile range) and nulliparous (98.6%). For women with at least 10 years follow-up (i.e. undertook PEF in 2009–2013; N = 514), 27.9% returned and thawed their frozen eggs (average time to return: 4.9 years). This reduced to 22.1% in those with at least 5 years follow-up (i.e. undertook PEF in 2009–2018; N = 4288). Of those who used their frozen eggs, 47% used donor sperm. After at least 2 years follow-up, 33.9% had a live birth, rising over time to 37.8% for eggs thawed between 2019 and 2021. Female age at egg freeze, number of eggs thawed, and year of egg thaw (but not length of freeze) were associated with the chance of a live birth following egg thaw. LIMITATIONS, REASONS FOR CAUTION In the timeframe 2009–2019, we did not have information on whether egg freezing occurred because of a cancer diagnosis, a cohort we wished to exclude from the study. As a result, for this timeframe, we weighted observations by the probability that egg freezing occurred due to cancer, with the prediction model developed on the years 2020–2023. Changes in laboratory and clinical practice over time, along with shifting indications for PEF may limit the generalizability of the study egg thaw outcomes, which are biased towards ‘early adopters’ of PEF. WIDER IMPLICATIONS OF THE FINDINGS This study provides recent and comprehensive data on PEF to guide prospective patients and clinicians and inform policy. The exponential growth in PEF in Australia and New Zealand mirrors trends in other high-income countries, suggesting a doubling time of 2–3 years. Study findings highlight the need for setting realistic expectations about the likelihood of returning to use frozen eggs and live birth rates. FUNDING This study was funded by the Australian government through the 2020–2025 Medical Research Future Fund (MRFF) Emerging Priorities and Consumer Driven Research initiative: EPCD000014 DISCLOSURE(S) G.M.C. declares funding from the Fertility Society of Australia and New Zealand, paid to her institution, for management of the Australian and New Zealand Assisted Reproduction Database (ANZARD), the data source for this study. E.K. declares being a previous employee of THEMA Consulting Pty and a current employee of Ferring Pharmaceuticals Pty Ltd. I.R. declares being a Board Director of the Fertility Society of Australia and New Zealand (Psychosocial/Counselling Representative). All other authors declare no conflict of interest. TRIAL REGISTRATION NUMBER N/A.