First, the problem that egg freezing is trying to solve:
As a society, we are having children later in life. Today, most first-time, college educated mothers will have their first child after the age of 30, and likely try for a second in their mid-30s.
The issue: as women enter their mid-30s, their fertility begins to decline, and for women trying to conceive in their late-30s or early-40s, things get dramatically more difficult.
The culprit in all of this is that as a woman gets older, both the quantity and the quality of her eggs begins to decline, and thus the likelihood she’ll produce a single good egg in a given month diminishes.
A proxy for this is the proportion of eggs go on to make high quality embryos, and as you can see that blend erodes with time.
The Good News
An interesting thing about our biology is that the quality of a woman’s eggs typically declines faster than the quality of her womb, and her ability to carry a pregnancy. So the premise, and hope, of egg freezing is that extracting and freezing eggs while a woman has more high-quality eggs will allow her to thaw them and use them later if she has trouble conceiving on her own.
It’s leveraging the disparity in time between when most women’s egg numbers and quality goes down and when they physically can no longer carry a pregnancy in utero.
Egg Donation & Why It’s Relevant
Egg donation came about for this precise reason: When women no longer have high quality eggs of their own, they often choose to purchas and use “donor” eggs, which are usually eggs from a much younger women. Making embryos from these younger, higher quality eggs, drastically improves many patients’ odds of a successful pregnancy.
But there are many reasons why egg donation isn’t a cure-all. Most importantly, to use donor eggs means foregoing biological ties between mother and baby. If you talk to anyone who has used donor eggs, they will tell you this decision can be incredibly difficult from an emotional perspective.
Why is egg donation relevant to egg freezing? Well, because egg donation and egg freezing are essentially the same concept – taking the eggs of a younger woman with healthier eggs and transferring resulting embryos into the womb of an older woman. But, when you freeze your eggs, you play the role of both donor and recipient (if you ever come back and use the eggs).
With that, there are three things to know about egg donation.
First, egg donation works. When a 42-year-old woman tries to conceive with her own eggs using IVF, her live birth rate is only around 4% per cycle. When that very same woman uses higher quality donor eggs, her live birth rate climbs to 60% per cycle.
Now, for many people new to fertility treatments, having something work 60% of the time might sound like a failure. But that’s actually the most successful fertility treatment we currently have.
Second, egg donation is not fringe. We have been doing it for years, and its volume continues to grow because its success is reproducible across women of all ages and backgrounds.
Finally, egg donation works whether we are doing a “fresh” transfer, or freezing eggs and then thawing them, just like we do with egg freezing.
Enough about donors - what do we know about birth rates for women who electively froze their own eggs?
Only a few studies have followed women who have frozen their eggs electively (not because of any fertility issue) and then returned to use those eggs. The studies we do have show that egg freezing “works” better for some patients than others, and most of this hinges on how old you are at the time you elect to freeze your eggs.
As you can see below, one recent study found that of patients 35 or younger who froze 10 eggs, 50 – 60% who used those eggs had babies with them. Of the patients who froze 10 eggs at age 36 or older, approximately 30% had babies using those eggs.
A similar exercise was done at Brigham & Womens and Massachusetts General Hospital and here is how the results broke down.
What’s embryo freezing?
Some doctors will mention the concept of freezing embryos rather than freezing eggs, which means freezing an egg that’s been fertilized with sperm and has typically grown for five days into what’s called a blastocyst. There are a few reasons why a doctor will broach the concept of freezing embryos.
First, historically, we weren’t great at freezing eggs. We’ve gotten a lot better at freezing and successfully thawing them, thanks to the advent of a quick-freezing technology called vitrification, rather than the slow-freezing process that was used in the past. While many labs are very successful at using this process, embryos are still more stable than an egg frozen alone.
Another big argument for freezing embryos, rather than eggs, is that you’ll have a better sense of the quality (and therefore success rate) of what you freeze. Making embryos means putting eggs through a number of natural hurdles – to be successful, the egg must be capable of fertilizing and growing into a high-quality blastocyst. There is simply no way of knowing whether individual eggs are any good, but getting through the fertilization process will give you many more indications. Below you can see the probability of a live birth by maternal age and number of embryos.
If you talk to patients who have done IVF or thawed eggs, you’ll hear that it’s not infrequent for the “funnel” to narrow very quickly as they go from eggs to embryos. For example, many patients can go from 20 eggs to one or two embryos. Knowing in advance (i.e. before you plan to or need to use the eggs or embryos) is helpful. But, there are many associated costs no matter when the "funnel" is deteremined, from the financial (purchasing donor sperm if that’s needed, and the laboratory costs of growing embryos) to the emotional (foreclosing the option to fertilize these eggs with a future partner’s sperm later).
To conclude, the field does have a fair amount of experience with frozen eggs – much of that has come from years of using donor eggs, and recently we’ve amassed more data on women who have electively frozen eggs and used them to have children later. While we know that we have the ability to freeze eggs, thaw them, and see them fertilize and eventually become healthy babies, we also know that the performance and success of frozen eggs hinges primarily upon the age of the woman at the time of the procedure.