Accurate egg freezing success rates have been notoriously difficult to pin down, in part because women who freeze their eggs typically don’t use them for years after freezing and in part because egg freezing technology is advancing faster than data collection. But a new model that considers two factors—a woman’s age at the time of freezing and how many eggs she’s frozen—gives us a very helpful tool for predicting an individual woman’s chance at live birth after egg freezing.
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Developed by researchers at Brigham and Women’s in Boston, led by Dr. Janis Fox, the model was based on a study of 520 healthy women undergoing IVF with ICSI (none of these women were infertile, and all were undergoing treatment for male-factor infertility). It makes two assumptions: one, that frozen and later thawed eggs will have a similar pregnancy and birth rate to “fresh” (recently retrieved) eggs—an assumption based on evidence provided by a large clinical trial published in 2010—and two, that 85–95% of eggs retrieved will survive the freezing and thawing process. (The freezing technique used here at Extend Fertility, called Cryotec, actually has an even higher egg survival rate—near 100%.)
The study, published early this month in the journal Human Reproduction, predicts that women 35 or under who freeze 10 eggs have about a 70% chance of at least one live birth later on. If they undergo a second cycle and increase that number to 20 eggs, their chances jump to 90%.
This new model is especially important because it predicts success based on the woman’s age at the time of freezing down to the individual year, whereas previous studies have clumped women into age groups such as “35–40 years old.” This is key, because doctors know that fertility changes drastically throughout a woman’s 30s.
“This is among the best, most relevant studies published on the subject so far,” explains Dr. Joshua Klein, chief clinical officer here at Extend Fertility. We’re excited to use this new data to help women make even more informed choices about their health and their lives.
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