One major weakness of egg freezing is that there is no way to test the quality of eggs on their own. So you won’t really know the potential of what you froze until you decide to use your eggs. In contrast, embryos must overcome many crucial hurdles that will give your doctor a much better sense of their quality, and their likelihood to result in a baby later. This has led to a healthy debate as to whether, when preserving fertility, freezing eggs is best, or freezing embryos is better.
There are compelling arguments on both sides that you’ll want to understand before making this very personal decision, and we’ll walk you through them.
When a woman freezes eggs she is “flying blind” when it comes to her visibility into whether those eggs can actually lead to a live birth. That’s because there’s no way to test eggs on their own to determine their quality, and the following crucial hurdles remain:
This can lead to a problematic situation where a woman’s eggs don’t perform as well as she would have liked but, by the time she realizes this, her egg quality has declined further -- with perfect information she may have chosen to freeze more eggs up front, but she didn’t find out until it was too late.
Conversely, women who freeze their embryos have much greater insight into whether what they’ve elected to freeze will lead to a live birth. That’s because turning eggs into embryos requires that they be successfully fertilized, and that those embryos survive until a point when they can be frozen, which is usually blastocyst stage (around the fifth day of development). Embryos are graded at each point in their development, which reflects an embryologist’s opinion of whether they are high quality or not. Finally, with embryos you have the option to run a genetic screening test on them with hopes of predicting more accurately whether they’re likely to become healthy babies.
Below we show what an egg freezer knows. We also include what an embryo freezer knows (with two scenarios as examples).
Here, the woman who froze her eggs knows that she has stored 15 eggs. She knows nothing else.
Alternatively, the woman froze embryos has a more enlightened point of view on those 15 eggs. In scenario #1, the embryo freezer may be comforted with the result and choose to not undergo another cycle. Risk still remains that her three embryos will not lead to a live birth, but many unknowns have been addressed. On the other hand, if this woman ends up in scenario #2, she’ll learn two things. First, her efforts won’t yield a child. So she may want to do another cycle. Second, she may pick up on an important clue about her laboratory’s ability to work with her eggs (very few fertilized and none become embryos). That may inform her decision of whether to go to a different clinic. So, as you can see, women who elect to freeze embryos have a tremendous information advantage.
Embryos are typically more robust than eggs and thus are easier to freeze and thaw. This is demonstrated by the fact that excellent laboratories manage to successfully thaw 99% of frozen blastocyst embryos, and minimally competent labs can thaw 90% of them.
Freezing embryos is extremely common. In fact, the majority of IVF transfers in the US now use embryos that have been frozen. So it’s likely that your clinic has a proven track record of freezing and thawing embryos (though you should verify this).
Historically, freezing eggs was much more of a gamble. This has started to change with the advent of better freezing technology called vitrification. Now, in excellent labs, they expect 90% of the eggs that they freeze to survive a thaw, and in minimally competent lab it’s closer to 80%.
Some labs are excellent at freezing and thawing eggs. As you can see from one lab’s data below, they show no difference in results when doing IVF with fresh eggs or frozen eggs. Often, the clinics with the best results publish their track record.
Yet rarely is the rest of the field anywhere near as competent. In this case, most clinics have minimal experience freezing and thawing eggs, let alone enough of a proven track record to publish their performance. Thus, it would be a mistake to automatically presume your clinic’s laboratory achieves similar results.
So, it is generally accepted that there’s a higher chance of embryos surviving a thaw than eggs, but it’s crucial for you to investigate what the capabilities are of your lab so you can understand if the added risks are minimal.
The down-the-road, non-medical implications are where the arguments for egg freezing really grow strong.
First and most obviously: freezing eggs will allow you the flexibility to choose who the genetic father of your children will be. This could be a future partner or a donor. Since life flexibility is a big reason people think about freezing eggs in the first place, this is clearly a huge draw.
Legally, embryos can also be more difficult.
When making embryos, you have the choice to use a sperm donor either anonymously from a sperm bank or someone you know, or a current romantic partner like a boyfriend or husband.
Using a sperm donor from a sperm bank gives women legal authority over the embryos. It’s when a partner is used that things can get very complicated -- there are plenty of legal cases that have cropped up in different states recently in which a woman has wanted to use the frozen embryos, but the male partner has successfully blocked her from doing so. If you’re using a romantic partner or even a known donor like a friend, you’ll definitely want to meet with an attorney specializing in reproductive technology beforehand so that you can ensure you’ll have full rights to the embryos.
Finally, there’s a legal unknown, as congress has continued to propose legislation that would say life begins at conception. It’s unclear what the implications would be for existing embryos, but it could make it harder to figure out what to do with them if you don’t ultimately end up wanting to use them.