Freezing eggs vs freezing embryos: which is better?

More women than men are enrolled in medical school these days, a long overdue sign of the times that we may be finally approaching equality (albeit, with still a long, long, way to go).  Yet while the socioeconomic tides may be turning, the biological clock ticks on. The hard-fought opportunities that are now available to young people with ovaries can force the difficult choices between pursuing professional goals, or putting them on pause to start a family.

Luckily, we live in an amazing era of modern medicine where fertility preservation is not only a viable option, it’s mainstream, as described by my favorite medical journal, the New York Times.  At Olive, we have certainly seen an uptick in the volume of patients seeking fertility preservation, in spite of, or perhaps because of, COVID19.

However, from patients seeking to preserve their fertility, one of the most commonly asked questions is if it is better to freeze eggs or embryos?

The question is typically asked from the perspective of success rates. Which approach is more likely to eventually result in a healthy baby? The Google machine will often lead them to the conclusion that embryos survive the freezing process better. While this was true in the bygone times, as discussed here, thanks to advances in vitrification, oocyte and embryo cryopreservation are both highly successful, and survival rates are essentially equivalent when performed by expert embryologists such as ours. From the technical standpoint, if your embryos can be frozen, so can your eggs.

So, the question of freezing eggs vs embryos is not really a technical quandry, but rather, a practical one.  Let me try to explain with a sport analogy (caveat emptor- I am mediocre at both sports and analogies): the ovaries are the starting line, the uterus is the finish line, and between the two there are several hurdles.

When you freeze eggs, you have cleared the first hurdle, but there are more ahead that need to be jumped before you cross the tape. However, you won’t know how far you are going to get until you come back one day, to thaw those eggs (hurdle), fertilize them (hurdle), watch them develop into blastocysts (hurdle), then possibly perform genetic testing to find a normal embryo (hurdle). It is possible, unfortunately, that when you come back to use the eggs, potentially several years later, that you get tripped up on one of those hurdles, the eggs don’t result in healthy embryos, and you are scratched from the race. You could go back to the start, but now you’re a few years older, and the odds of making it to the finish line are that much lower.

On the other hand, when you freeze embryos, you have already cleared most of those hurdles, so you can take a break from the race in confidence, knowing that when you return you are already almost at the finish line. In the worst-case scenario, even if you learn that you have no healthy embryos to freeze now, at least there is an opportunity to go back to the starting line sooner rather than later, with fresh “leggs” (see what I did there?). (Actually, the race goes on, with the hurdles of embryo implantation and beyond, but that’s a discussion for another time…).

The big difference, in case it is not obvious, is that in order to make embryos, you need sperm. For single women who are not interested in using donor sperm or are hoping to preserve their chances for a future partner, freezing eggs is the only practical option. On the other hand, if one is in a committed relationship or is comfortable using donor sperm, then freezing embryos is a possible choice. Some patients may even decide to freeze half of their eggs and fertilize the other half, which sounds like the best of both worlds, but comes with its own limitations, especially when the starting egg number is on the low side.

Thus, the answer to the question, “Is it better to freeze eggs or embryos?”, is the one that you will often here when it comes to personal choices: it depends. There are pros and cons to both approaches. Talk to your team at Olive to figure out what is best for you.