Fertility Preservation for Cancer Patients

A question some cancer patients may face is whether they’d prefer to freeze eggs or have their eggs fertilized and freeze embryos. Given the tight timelines cancer patients face, this is likely more of a decision faced by patients who have easy access to sperm (namely, those in a relationship with someone they want as the genetic parent of their child.)

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 person freezes eggs they are “flying blind” when it comes to their 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:

• Warming the eggs
• Fertiization
• Growing embryos
• Transfer
• Implantation in the uterus
• Healthy pregnancy

This can lead to a problematic situation where a person’s frozen eggs don’t perform as well as they would have liked but, by the time they realize it, their fertility may be compromised through cancer treatment or they have aged out of a window where one’s own eggs are likely to work.

Conversely, those who freeze 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 have them genetically screened 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).

As you can see above, the person who froze their eggs knows that they have stored 15 eggs. They know nothing else. Alternatively, the person who 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 (e.g. 3 genetically-normal embryos were created) and choose to not undergo another retrieval. Risk still remains that the three embryos will not lead to a live birth, but many unknowns have been addressed. On the other hand, if this person ends up in scenario #2, they’ll learn two things. First, their efforts won’t yield a child because no embryos were created. So they may want to do another retrieval (should the timeline of cancer treatments allow for it.) Second, they may pick up on an important clue about the laboratory’s ability to work with their eggs (very few fertilized and none become embryos.) That may inform their decision of whether to go to a different clinic. So, as you can see, people 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. Today, the majority of IVF transfers in many countries 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.)

In contrast, 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 many labs, 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. When the U.S. National ART Surveillance System reviewed data from the entirety of 2013, they concluded, "There was no evidence of differences in ART outcomes between autologous fresh and cryopreserved oocyte cycles".

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 other genetic parent 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, someone you know, or a current romantic partner.

Using a sperm donor from a sperm bank gives the embryo freezer legal authority over the embryos. It’s when a partner’s sperm is used that things can get very complicated—there are plenty of legal cases that have cropped up in different regions recently in which a person has wanted to use the frozen embryos, but their partner (or ex-partner) has successfully blocked them from doing so. Below is one such headline where a cancer patient was blocked from accessing embryos she helped create. If you’re using the sperm of 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 and have your consent forms reflect your decision on disposition.