What's The Difference Between Freezing Eggs And Freezing Embryos?

Those of you who like to spend your precious downtime reading celebrity gossip might have noticed that a few months ago, Modern Family star Sofia Vergara's ex sued her over their frozen embryos; the couple had two frozen embryos remaining from their time together, and Vergara's ex-fiance, Nick Loeb, sought the legal right to have a surrogate carry the embryos to term and raise the resulting children as his own. You may have pondered many questions as you analyzed this very pressing cultural issue — like, can you believe her ex wrote an op-ed about their legal fight over the embryos in the New York Times? What would I do if my ex wrote about our crappiest break-up moments in the New York Times? How does Sofia Vergara get her hair so glossy? — but another set of questions may have popped into your head, too. Like, what exactly is a frozen embryo? How is it different from freezing your eggs? And why would you freeze embryos instead of your eggs?

Over the past few years, there's been a lot of think pieces and op-eds about freezing eggs, most of them examining whether egg freezing technology is a revolutionary tool that will help women develop families at their own pace, or a medical procedure so pricy and experimental that it won't change things any time soon. But despite all this cultural chatter about the procedure, most of us don't know much about what exactly "freezing your eggs" entails — and we know even less about what freezing an embryo might entail. So let's journey together, you and I, and find out the real difference between frozen eggs and frozen embryos. Who knew you could freeze so many different things that come out of your uterus, right?

What Is A Frozen Egg?

Oocyte cryopreservation, typically known by the more spell-check friendly name of "freezing your eggs," involves collecting and then freezing your unfertilized eggs, so that they can be stored and later fertilized. How exactly does this work? As our sexual health columnist Emma Kaywin explained in her post on egg freezing, each month, when we ovulate, one egg (of the 30,000 we have when we hit puberty) matures and releases. When an egg is released, it's ready to party (aka get fertilized) by any stray sperm that happen to wander across its path.

When you freeze your eggs, a large number of eggs are harvested from your body at once, and preserved through cryptopreservation as they are — unfertilized (meaning: no sperm have come into contact with them at all). When the time/ sperm is finally right, the eggs are unfrozen, and used in a process called in vitro fertilization — which means that the eggs and sperm are combined by doctors in a lab, and when fertilization is successfully achieved, the eggs are then implanted into your uterus or the uterus of a surrogate.

What Is A Frozen Embryo?

The process of freezing embryos is very similar to the process of freezing eggs — but instead of just freezing unfertilized eggs, eggs and sperm are combined pre-freeze, using IVF. The fertilized egg creates a zygote, which then develops into an embryo — the earliest stage of pregnancy development (the embryonic stage lasts from fertilization through the next eight weeks; after that, the next development phase is fetus).

That embryo is then frozen, using similar techniques to those used in egg freezing — but since the fertilization process has already taken place, there's less of a "guess" factor than there is with eggs, and thus the odds of it resulting in a successful pregnancy are higher. When the embryos are unfrozen, they are placed in your uterus or the uterus of a surrogate to be carried to term.

How Do You Decide Which One You Want To Freeze?

Egg freezing and embryo freezing are utilized for many of the same reasons: a woman wants to become pregnant in the future but is unable to carry a pregnancy to term now; a woman is about to undergo a medical treatment that will damage her eggs or render her unable to carry a pregnancy to term in the future, and she wants to still be able to have children using her own genetic materials. Sometimes, however, freezing an embryo is actually part of a woman's active fertility treatment — a recent study found that, for women undergoing IVF, embryos that were briefly frozen had a higher rate of resulting in a successful pregnancy than embryos that were implanted into uteruses directly after fertilization.

The obvious difference between the two procedures is that frozen eggs are unfertilized, while frozen embryos have begun the earliest stages of pregnancy development. This means that a woman who has frozen her embryos has found the sperm she wants to use for a pregnancy (from a partner or donor), while a woman who freezes her eggs may still be looking. So freezing embryos is only an option for women who've found sperm that they liked so much, they wanted to put an egg on it. Some people also have religious or ethical issues regarding embryo freezing, because it involves successfully fertilized eggs — issues that they typically do not have regarding frozen eggs.

So how do you decide? For most people, it's about what materials you have to work with — since frozen embryos result in a successful pregnancy more often than frozen eggs, many doctors consider freezing embryos the better option. But that's only an option if you have sperm that you want to fertilize your eggs available — and since many women freeze their eggs because they have yet to meet a partner or seek out a donor, freezing an embryo is not really an option.

Of course, should you actually want to freeze your eggs or embryos, your doctor can explain it much more in-depth than this. But hey, at least now, you understand Sofia Vergara on a deeper level. Don't you feel like you guys could totally be friends?

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