While right now we have no way of freezing the biological clock, modern technology has given us a type of “snooze button.”

Freezing of eggs and embryos, otherwise known as cryopreservation, preserves these fertility keys at the biological age they were when frozen. Since the major factor in viable pregnancy and birth is the age of the egg and not the age of woman carrying the baby, this is great news for those women whose biological clocks are sounding alerts.

If you’re thinking about going this route, the next big question to ask is: are you going to freeze your eggs or your embryos?

This is not a simple decision, with many questions to ask and factors to consider before you begin. Below follows an extensive list of factors to help you decide which path is right for you.

Physical Factors

A Little Bit of Background

The initial stages of egg freezing and embryo freezing are the same. You’re given medications which increase your ovulation and get more eggs ready than usual. The eggs are then harvested from your ovaries (an intravaginal procedure done under sedation).

This is the last stop if you’re freezing your eggs. If you’re planning on freezing embryos, on the other hand, now is time to go ahead and make those eggs into embryos. To do so, of course, you’ll need sperm - from your partner or from a donor - to fertilize the egg. If the egg fertilizes, it will be frozen once it has multiplied and reached approximately 50-100 cells.

This brings us to the first major factor in deciding between freezing eggs and freezing embryos:

Need for Sperm

Yes, it may be obvious, but we’ll point it out anyway: you need sperm to create an embryo. If you have a partner that you’re sure you want to have children with at a later time, or if you’re planning on using donor sperm anyway, then there are no obstacles to creating and freezing embryos.

If you’re single and still hoping to find the right partner to raise a family with, freezing eggs may make more sense. All you need for that is one party - YOU.

Freezing and Thawing Success Rates

Eggs are more fragile than embryos, as they are only one cell (not 100), and that one cell is mostly water. But while earlier methods of egg freezing often created issues when the egg was frozen or thawed, the vitrification (flash-freezing) process that has become common in the past few years has brought success rates of frozen eggs up to par with those of fresh eggs.

Known Fertilization Rate

When you freeze embryos, you know exactly how many fertilized embryos - how many chances at a viable pregnancy - you’re preserving. When you freeze eggs, on the other hand, you don’t know how many of them will fertilize when thawed.

That said, creating each IVF embryo usually requires multiple eggs anyway. This sample chart shows 2 viable embryos developing from a group of 12 eggs that were retrieved (obviously an individual’s results may vary). Assuming you matched this chart, as long as you froze all 12 eggs, it would basically be equivalent (probability-wise) to freezing 2 embryos.

Live Birth Success Rate

As we all know, a viable egg - and even a fertilized embryo - do not (unfortunately) guarantee a successful pregnancy and birth. But do you have a better chance at a live birth when you start with a frozen embryo - or with a frozen egg?

The UK’s HFEA (Human Fertilisation and Embryology Authority) reports the following birth rates for frozen embryos using a woman’s own eggs and partner’s sperm, based on age of woman at transfer:

Under 35 - 27%
35 - 37 - 26%
38 - 39 - 21%
40 - 42 - 15%
43 - 44 - 8%
45 and up - 4%

Since reliable methods of freezing eggs are a more recent development, we have less data on frozen eggs (and especially on women using their own frozen eggs) than on frozen embryos.

What we do have, according to the HFEA, is a birth rate for frozen donor eggs in 2016 that was around 30%. This is comparable (and maybe even a little better) than the above rates for frozen embryos, but it doesn’t divide the data by the age of the woman at transfer.

The average birth rate for women using their own frozen eggs was 18%, which is similar to the birth rate for frozen embryos for women who at transfer were approaching or after the age of 40.

The HFEA points out that a reason why the donor eggs led to more successful births was that they were in general frozen earlier - and we know that the age of the egg is one of the most critical components. Additionally, in order to donate eggs, women need to meet specific health criteria, which is not the case for women who freeze their own eggs - which results in the pool of donor eggs being overall “healthier.”

According to that, if you use your own young, healthy eggs, you would likely have better results than the average, potentially bringing it close to the rate for frozen donor eggs and frozen embryos.

A helpful tool in your decision may be the Brigham Women’s Hospital Egg Freezing Counseling Tool. It’s a research-backed calculator that predicts the likelihood of a live birth for women who choose to freeze their eggs and use them later. (Note: as per the disclaimer on the tool itself, while it is based on research, “This calculator is not externally validated, and as such, should be used with caution.”)

Ethical and Legal Factors

Dissolution of a Relationship

When you freeze embryos that were fertilized with a specific partner, in certain senses you’re locking yourself in. While you might be head over heels with your current partner, and convinced you’re going to build a family with him someday, life bears witness that relationships don’t always work out the way we plan.

Most consent forms for undergoing IVF and freezing embryos contain legal clauses that stipulate how ownership of the embryos will be divided if the relationship ends. That said, if the breakup is nasty, you might face legal hassles… if you even still want to use those embryos.

Egg freezing avoids all these issues. Your eggs are yours alone, to use if, when and how you want.

Treatment of Unused Eggs/Embryos

In practice, many women don’t end up using their frozen eggs and embryos, either because they conceived naturally, they decided not to have children, or they reached their ideal family size before using all the eggs/embryos. What happens to your genetic material once you decide you don’t need or want it anymore?

Many faiths consider an embryo a human life and have restrictions on how one can treat it, even if it is no longer needed. Aside from faith, it is not uncommon to feel uncomfortable about casually disposing of an embryo. Unfertilized eggs, on the other hand, are much simpler to dispose of, both emotionally and ethically.

Emotional Factors

An unexpected insight comes from Briallen Hopper, who found that having embryos (from donor sperm) safely frozen actually diminished her possibilities for romantic love.

In her early 40s, Briallen wants to have children - but men who want to have children are starting to rule her out as a potential partner. Her chances of conceiving naturally are getting significantly lower - and odds are slim that those family-oriented men would be interested in having a baby using an embryo that doesn’t include their genetic material!

Briallen’s frozen embryos from donor sperm may enable her to become a mother but, oddly enough, at the expense of becoming a romantic partner.

Egg freezing, by leaving open the possibility of who the father will be, doesn’t have the same impact on the way you feel about love - or on your romantic prospects.

Financial Factors

Neither freezing eggs nor freezing embryos is cheap. If your financial resources are limited, your choice between freezing eggs and embryos may depend on what procedures - if any - your insurance covers.

For Briallen Hopper, mentioned above, the financial aspect was critical in her decision. Egg freezing was prohibitive, but IVF was covered by her insurance, putting the embryo freezing process within reach.

Making Your Decision

Freeze eggs? Freeze embryos? It’s not a simple choice. You need to make a decision that includes your present and your future, your hopes and wishes, and your reality.

We hope that the different factors here leave you more informed about what the pros and cons of each process are. And we wish you clarity and satisfaction with your decision.