As a reproductive endocrinologist, one commonly asked question from my patients is: “Should I freeze my eggs or embryos?” When I respond that both are viable options the usual reaction is “Really? I’ve heard that it’s always better to freeze embryos”. Why is this a commonly held belief and how did we get to where we are?

History of Freezing Eggs and Embryos

A little background is in order. We’ve been successfully freezing embryos for over 30 years, since the first birth reported in Melbourne in 1984; since then, hundreds of thousands of children have resulted from this technology, and health outcomes of these offspring are at least equivalent to standard IVF with fresh embryos. Egg freezing, on the other hand, has posed unique challenges. The human egg is the largest cell in the body, which means that it contains a lot of water. Freezing an egg can result in internal ice crystal formation and these ice crystals can potentially wreak havoc within the egg (e.g. resulting in genetic damage). Additionally, hardening of the zona (shell around the egg) can lead to poor fertilization results after thawing and exposure to sperm. These challenges have been overcome in recent years with the introduction of vitrification (ultra-rapid freezing) and the routine use of sperm injection (ICSI) to achieve normal rates of fertilization. Cut to the present: success rates with frozen eggs are now neck-and-neck with fresh eggs

Why Freeze Eggs Versus Embryos?

The initial impetus for developing egg freezing programs was to afford single women an option that men have had for decades: not needing a partner or gamete donor if they required fertility preservation, a prime example being the single woman with cancer who is considering fertility preservation prior to potentially sterilizing chemotherapy. This has now been extended to single women considering “social” egg freezing, given the negative impact of advancing female age when family building is deferred to the future.

I frequently consult with couples who plan to defer having children for personal reasons yet want to hedge against the negative reproductive impact of female aging, as well as couples in their late 30’s or early 40’s who want to start their family now, but hope ultimately for a larger family size (more than one child). Why, then, not routinely advise that they freeze embryos (i.e. fertilized oocytes) given that this technique has been time–tried-and true for decades? Obviously this is a perfectly reasonable option. And yet, it’s only one of two reasonable options. I feel that it’s my responsibility to also present egg freezing. Too often the subject doesn’t come up (“of course you’d freeze embryos if you’re married”); why indeed should egg freezing still “be on the table”?

Less Fraught Questions of Dissolution

First, it is possible that excess embryos will be created that the couple may never need in the future, once they have attained their ideal family size. This can pose both a personal/ethical and practical dilemma. Storage entails a real, ongoing financial cost (often $300 - $1,000 per year), and many couples struggle with the alternatives of thawing and discarding versus donating their frozen embryos either for research or to other infertile patients. Some couples may feel compelled to undergo transfer of their frozen embryos even when they might otherwise not desire a larger family. Frozen eggs and sperm do not, independently, have the potential to initiate a pregnancy and thus the choices surrounding the disposition of stored gametes are less fraught.

Simpler Paths Forward During a Break Up or Divorce

Second, what if something happens to the couple’s relationship, such as a break up or divorce? Sperm and eggs belong to, and are of the individual partners, whereas embryos incorporate the germ lines of both. This possible eventuality is considered during counseling and during the consent process for embryo freezing, with specific stipulations and clauses dealing with separation and divorce (in addition to death of one or both partners). Although frozen embryos are legally recognized as joint property, and although future disposition under the above scenarios is incorporated into the consent forms, this will never entirely preclude the potential for costly and disruptive legal action by one partner or the other, especially in the event of a contentious or acrimonious split.

Optionality For Family Planning With A Future Partner

Finally, even single women considering egg freezing for fertility preservation commonly ask me whether they should freeze embryos instead (using donor sperm) or perhaps fertilize a portion of their eggs so as to freeze both eggs and embryos. If a patient is certain that she plans for single parenthood with donor sperm in the future, freezing embryos would of course make sense, especially given that how well the eggs might fertilize in the future is no longer an unknown variable. Yet still, I would counsel that should her life plans change she is somewhat “locked in” by having created embryos with donor sperm should she plan a family with a future partner. It‘s true that one cannot predict how many embryos might result from frozen eggs, but the counseling process should provide clinically established statistics regarding survival of eggs after thawing, expected fertilization rates and pregnancy rates per resulting embryo transfer. This calculus should of course be tailored to the individual woman’s specific case including her current age.

The bottom line:

Innovation and advances in egg freezing have now put women on more even footing with men in terms of their fertility preservation options (although obtaining eggs will always be a more clinically complex and invasive process than obtaining a sperm sample - not much we can do about that). A fully informed patient/couple can then make the best possible decisions for their reproductive care.