Writing in JAMA, a team of authors from the Center for Human Reproduction in New York tracked the outcomes of IVF cycles performed with either fresh or frozen (cryopreserved) eggs. They found that use of frozen eggs resulted in women having fewer live births compared to the former group, by a small but statistically significant degree.
'We were not surprised by the observed lower pregnancy rates with frozen eggs compared to fresh. However, we were pleasantly surprised that the pregnancy rates were still quite high for both frozen and fresh eggs,' Dr Vitaly A. Kushnir of the Center for Human Reproduction, first author of the study, told Healthline. 'Use of fresh eggs remains the gold standard since the pregnancy rates are superior and we have many years of experience and know much more about the safety of IVF with fresh eggs.'
Traditionally, donor IVF uses fresh eggs, which are fertilised immediately after retrieval and transferred to the recipient's uterus. However, owing to concerns over convenience and cost,the use of frozen eggs has swelled in recent years, especially as the American Society for Reproductive Medicine dropped the 'experimental' label on the technique of cryopreservation (see BioNews 681).
To directly compare the success of fresh and frozen eggs, the researchers examined data on US-based fertility clinics for the year 2013, containing information on 92 percent of IVF cycles performed in the country. Out of a total of 11,148 egg-donation cycles, 20 percent employed frozen eggs.
Their analysis revealed that for every round of embryo transfer, 56.1 percent of women using fresh eggs went on to have a live birth, compared with 47.1
The researchers ventured that, despite recent advances, the freezing and thawing process that a cryopreserved egg undergoes might still negatively impact its quality, resulting in the discrepancy in success rates.
However, they acknowledged the limitations of the study and the need for caution. First, the study was based on anonymised aggregate outcomes, without taking into account confounding factors such as the ages of fresh and frozen egg donors. Second, IVF cycles typically involve far more fresh eggs than frozen eggs, perhaps skewing the success rates towards the former.
Dr James Toner, president of the US Society for Assisted Reproductive Technologies wrote to The Washington Post: 'In traditional donor egg therapy (using fresh eggs), the recipient gets all the eggs the donor makes (typically 15-25). When frozen eggs are employed, only a batch of 6-8 eggs
'The good news is that there are more reproductive options now than ever, but we must proceed with caution,' commented Dr Kushnir. 'IVF is evolving quickly with many new techniques and technologies being introduced. It is important that before wide utilisation the safety and efficacy of each