How Egg Freezing Success Rates Change with Age

A few months back, a friend asked that I write about egg freezing:

“As a single woman in my mid-30s who has always been a strong maybe on kids (with preference for yes with right partner/financial circumstances), I’m now in a place where I feel like I need to start planning for either children and partner or freezing my eggs or SOMETHING before the options run out in the next few years… But most people online seem to be writing personal horror stories with multiple IVF fails.”

Many women face a similar quandary, wondering if they should freezing their eggs before it’s too late. Here’s what you need to know about egg freezing to make an informed decision.

Egg Freezing: A Brief History

Until recently, egg freezing was primarily a rare, last-ditch procedure, used mainly by young women to preserve their fertility prior to chemotherapy.

Nowadays, egg freezing is offered at about half of fertility clinics in the U.S. and sought out mainly by healthy women.

Contrary to popular stereotypes, women typically pursue egg freezing not to focus on their careers, but because they have yet to find the right partner.

“A lack of a relationship conducive to child rearing,” is the most common reason given for egg freezing, according to Dr. Nicole Noyes of the New York University Fertility Center.

How Egg Freezing Went Mainstream

In 2012, the American Society for Reproductive Medicine (ASRM) lifted the experimental label from egg freezing, although they stopped short of recommending it for “elective”, i.e., non-medical, purposes.

Then, last summer, Facebook and Apple announced they would cover the costs of egg freezing, up to $20,000, for their employees. Since their announcement, the number of women undergoing “elective” egg freezing has “skyrocketed” in the U.S. and rose an estimated 400% in the UK last year.

Not everyone is clinking champagne glasses over egg freezing going mainstream. A recent Slate magazine piece, for example, claimed that chances of success are so low“the chance that one frozen egg will lead to an eventual baby is a dismal 2–12 percent”that egg freezing “might be…a bill of goods.”

What companies offering egg freezing are really selling, the Slate article and others like it insinuate, is not a real chance at having a baby later in life but “hope, anxiety reduction, a break from the idea that you’re hurtling toward physical breakdown.”

But do the actual data suggest that fertility centers are peddling false hopes? Not at all.

In fact, most of the negative press gets the science completely wrong, so wrong that you have to wonder whether their coverage is driven not by data but by underlying emotional reactionsfear of “unnatural” reproduction,” or lingering sexist resentment of “narcissistic” career women who postpone childbearing to climb the corporate ladder, or resentment that women’s biological clocks tick faster than men’s.

Although I am not ready to declare that egg freezing implies “women’s emancipation is set in stone”, as some have, the available evidence suggests egg freezing is a viable, sound option for women who need to postpone childbearing.

IVF pregnancy rates using frozen eggs are now comparable to pregnancy rates using fresh eggs, according to the ASRM’s most recent review of randomized clinical trials. So, with some planning ahead, a 40-something-year-old woman can enjoy the fertility of her much younger self, much as one might lock in a good mortgage rate.

What Does Egg Freezing Entail? The Basics.

Egg freezing, or, in medical terms, oocyte cryopreservation, involves the retrieval, freezing, and storage of mature eggs from a woman’s ovary. As with regular IVF, a woman will typically take birth control pills for several weeks to suppress ovulation. At the beginning of her next cycle, she then injects hormones to stimulate the development of multiple egg follicles for about 10-12 days before her eggs are retrieved.

The eggs are retrieved using a needle inserted through the vagina and into the ovary, a procedure that does not require general anesthesia, only light sedation. The eggs are then frozen using either an older approach known as slow freezing, or a newer, faster approach known as vitrification.

In both vitrification and slow freezing, the first step is to dehydrate the egg cells. The water inside the eggs must be replaced with cryoprotectants so that ice crystals, which would irrevocably damage egg cells, cannot form. Next, in vitrification, the eggs are flash frozen by submersion in liquid nitrogen down to -196 ℃. In slow freezing, the eggs are brought down to -196 C in a series of successive freezes that takes several hours.

Slow freezing predominated until about 2009, when several clinical studies and a subsequent meta-analysis showed that vitrification leads to consistently and significantly higher rates of survival, fertilization, pregnancy, and live birth. As a result, most fertility clinics have switched to using vitrification.

Once a woman is ready to use her frozen eggs, they are thawed and then inseminated.

Egg freezing hardens the outer shell of the egg cell. Sperm cannot penetrate the outer shell of the thawed eggs to fertilize them. Instead, the clinic must select the most promising-looking sperm and insert them directly into the eggs with a needlea procedure known as intracytoplasmic sperm insemination (ICSI), originally developed as a treatment for male factor infertility.

Success Rates by Age at Freezing

The chances of achieving a live birth with egg freezing are not as well established as the success rates for IVF using fresh eggs or frozen embryos. Egg freezing is such a new procedure that what we know comes from only a handful of small studies.

The ASRM recently summarized the results of several small randomized control trials comparing IVF cycles using fresh eggs with IVF cycles using frozen eggs. The chances of a live birth ranged from 4-14% per egg frozen. The per-embryo transfer success were better, ranging from 35-61%, and were statistically indistinguishable from the per transfer success rates seen in cycles using fresh eggs.

As with other fertility treatments, the chances of success hinge largely on a woman’s age at freezing. A meta-analysis, led by Aylin Cil of New York Medical College and published in 2012, provides the most recent summary of how age at freezing affects the chances of achieving a live birth. Cil analyzed the outcomes from a total of 2,265 thawing/warming cycles involving 1,805 patients:

Screen Shot 2015-05-22 at 9.48.56 AM

Data taken from Age-specific Probability of Live Birth With Oocyte Cryopreservation: An Individual Patient Data Meta-analysis (2013) Cil et al., Fertility & Sterility

The chances of success were consistently higher with vitrification. Vitrification led to higher survival rates upon thaw (85% versus 75%), higher fertilization rates (79% versus 75%), and, most importantly, higher live birth rates, as shown above.

The number of embryos transferred also affected the chances of a live birth.

Screen Shot 2015-06-02 at 9.17.21 AM

Data taken from Age-specific Probability of Live Birth With Oocyte Cryopreservation: An Individual Patient Data Meta-analysis (2013) Cil et al., Fertility & Sterility

How Egg Freezing Stacks Up Against IVF with Fresh Eggs and Natural Conception

At first, a 20% chance of pregnancy for a woman who freezes her eggs at age 35 at first seems underwhelming. But it is actually comparable to her chances of conceiving naturally between the ages of 35-39, and it is greatly superior to the 13% chance the average woman faces using IVF with fresh eggs at age 41, or the truly dismal 5% chance she would have undergoing IVF at age 43. Consider the success rates for IVF using fresh eggs in 2012, reported by the Centers for Disease Control (CDC):

CDC 2012 Live Births from All US ART Cycles

CDC 2012 Live Births from All US ART Cycles

Why These Success Rates Are Higher Than 2-12%

The live birth rates for vitrification shown above are the chances of a live birth after an embryo transfer. This is not the same as the chances of a live birth per egg retrieved, which are closer to 4-14% for vitrification, according to the ASRM. The 2-12% rate refers to the per-egg chances using the older approach of slow freezing.

IVF with frozen eggs is a leaky process: some eggs will be lost at each step in the process. Not all eggs survive thawing. Of those that survive, not all fertilize. Of those that fertilize, not all develop into healthy 2-3 day embryos that can be transferred. Not all embryos implant. And not all the resultant pregnancies are viable.

The inevitable losses at each step in the process are why many doctors recommend that women store around 20 eggs. Storing 8 eggs or more doubles the chances of success, from 22% to 46%.

Note that the per egg success rates for IVF with fresh eggs, or for trying to conceive the old fashioned way, are similar to those for frozen eggs. This is why I believe the 2-12% chance of success statistic is incredibly misleading.

The Downsides

Egg freezing has some potential downsides. For one, the financial costs are considerable.

The whole process, from freeze to thaw to a single transfer, costs around $20,000, assuming the first transfer is successful.

Women who require multiple thaws and embryo transfers to achieve a live birth will pay considerably more than $20,000, with each additional round adding between $3,500 and $5,000.

As Dr. Noyes of the New York University Fertility Center notes, “for now, without insurance coverage, [egg freezing] is a rich person’s game.”

And, although the initial data are reassuring, we still do not really know whether babies conceived via egg freezing are at a higher risk of birth defects or behavioral disorders. Initial research on 900 births after egg freezing found that the rate of birth defects was 1.3%, much lower than the 3% rate of birth defects in the general population. Still, we need larger studies to fully assess the potential risks.

Another concern is the mandatory use of ICSI. Freezing hardens the outer shell of the egg, rendering it impenetrable to sperm. Because sperm cannot penetrate and fertilize the thawed eggs, a single sperm must be selected and injected directly into the egg to fertilize it.

Why is the use of ICSI worrisome? For IVF using fresh eggs, ICSI has been linked with a slightly increased risk of autism compared to autism rates for IVF without ICSI. Still, the overall rate of autism with either procedure remains low, about 1%. And no one knows whether the apparent increase in autism stems from the underlying fertility problem leading to the use of ICSI or from ICSI itself. (This topic is so complex that I will cover it in a separate upcoming post.)

The Bottom Line

Despite these potential downsides, if I were in my late 20s or early 30s and single, I would freeze my eggs, as a hedge against future infertility and for general peace of mind.

I would take care, though, to find a clinic with real experience in egg freezing using vitrification. Vitrification is such a novel procedure that many clinics that offer egg freezing have never performed even a single thaw. Moreover, the techniques for vitrification are not standardized, so techniques and success rates can vary considerably from clinic to clinic.

On the other hand, if I were partnered and in a what looked like a strong, committed relationship likely to stand the test of time, I would freeze embryos created with my partner, not eggs. Embryo freezing is a much more established, low risk, and time-tested means of preserving fertility.

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About Amy Kiefer

I am a research scientist and mother of two. I was born in Chicago, but for the past 10 years I have lived in the San Francisco Bay Area with my software engineer husband (a cliché, I know). I love digging into the scientific literature and summarizing research findings. In this blog, I try to present an unbiased and sane take on research topics of interest to soon-to-be and new parents.
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2 Responses to How Egg Freezing Success Rates Change with Age

  1. Pingback: Fertility in Your Late 30s: 7 Things You Need to Know | Expecting Science

  2. Anonymous says:

    This is a great article – very honest yet not depressing. thank you!

    Like

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