Baffled by Numbers

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How Eggs Are Different From Frozen Waffles

Retrieve eggs, freeze them, relax—but don't get too comfortable.

The NY Times recently published an article titled: "So Eager for Grandchildren, They’re Paying the Egg-Freezing Clinic," describing a recent phenomenon, where women, mostly above the age of 35, freeze eggs, hoping to use them to conceive in the future. Entourages of women and their parents show up at clinics, with the hope of stopping the biological clocks of yet unwed daughters. Yet to what degree are these hopes justified?

As the title suggests, there's some equating between eggs and grandchildren. One of the would-be grandmothers related to the 26 eggs taken out of her daughter's body as "I have 26 grandchildren!"

Well, not quite.

The article cautioned that "because it offers no guarantees and is still considered experimental by the American Society for Reproductive Medicine, a professional association, it can seem to some like an extravagant gamble." But the only ones who spoke about this being a potential, not a promise, were the physicians interviewed. The women and their parents, on the other hand, touted the calmness the procedure brought, alongside the hope of holding a grandchild some day. Psychology tells us that people prefer certainty over uncertainty. And when faced with the latter, especially in emotionally laden situations, they turn it into the former.

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The article also mentioned that over 2,000 babies were born of frozen eggs worldwide, most through egg donation. This means the eggs were taken from women who are mostly under 30, whereas most women who choose to freeze their eggs for their own future use are at the end of their 30s.

In order to evaluate the success of egg freezing, one would want to know how many fertilization attempts have led to these 2,000 deliveries. In other words:Are these 2,000 deliveries out of 2,000 attempts, or are we looking at far lower success rates? This is a common oversight in risk communication, which does not allow anyone interested in the procedure to know what her chances are of conceiving thanks to the freezing.

These chances depend on the woman's age when freezing, the number of eggs frozen, and the chances of egg survival once frozen. Starting in the early 30s, women experience a drop in the chance to naturally conceive. This drop accelerates with every year over age 37, until age 45, when deliveries stop.

According to some models, about a third of 40-year-old women will no longer deliver (more conceive, but miscarry). Current fertility treatments are not particularly efficient at stopping or reversing this natural process. Further, the number of eggs varies between women. Whereas the NY Times article described a woman who produced 26 eggs, data presented at the recent annual Israeli Association for the Study of Fertility indicted that the average number of eggs frozen per patient attempting 'social' egg freezing, mostly at age 37-39 in Israel, a fertility empire, was 10.

The survival rates for eggs frozen at the end of a woman's natural reproductive lifespan, in her late thirties, remains to be determined. Freezing eggs for donation when the woman is in her 20s is a highly efficient process. But it is highly likely that the success rates will be significantly lower 10 years later. Thus, the younger the woman when freezing eggs, and the more eggs she freezes, the greater the chance of a delivery using such eggs. Currently, most women who turn to egg freezing are in their late 30s.

The technology that allows for egg freezing is a genuine breakthrough that can preserve the ability to deliver at an age when natural conception would not occur. But in order to make the most of this technology, it needs to be used at an age when the woman's chances to get pregnant naturally are high—that would be around 30 (if not earlier), and certainly before 35.

Freezing eggs close to the age of 40 may create the illusion of certainty around having a child. The title of a blog one of the women writes "RetrieveFreezeRelax" expresses this false concept, which may end in bitter disappointment.

This posting was written with Avi Tsafrir, MD., Reproductive medicine specialist at Shaare Zedek IVF unit, Jerusalem, Israel. Dr. Tsafrir's main research topic is reproductive ageing.

Talya Miron-Shatz, Ph.D., is a researcher at Princeton University. She specializes in medical decision making of patients and health professionals.

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