Debunk Myths About Egg Freezing Success Rates

What? Seventy or eighty percent of success rate?? If you hear a clinic’s blunt claim, run as fast as you can!

Yes, your frozen eggs resulting in a live birth when you decide to use those eggs is not 100% guaranteed. The human body is so complex and each body is unique, perfect solutions and iron-clad promises are impossible. HOWEVER, with science and data on our side we can examine the statistics and understand what they implies for egg freezing success rates.

What’s the data on egg freezing success?

There is no widespread published data on the live birth rates for social egg freezing yet. The 4 decade long history of the procedure was mostly done for cancer patients attempting to preserve their fertility before chemotherapy. Egg freezing by healthy women is a newer phenomenon so there just hasn’t been enough time to gather strong, reliable numbers. Women may wait up to 10 years before using their frozen eggs or they may end up in a relationship and conceive naturally or never use the eggs at all, meaning there is no date available to collect data from them. But we do have compelling evidence from other contexts that supports the idea that using frozen eggs for IVF offers a significant chance of success.

The most interesting research is from data over donor eggs. Egg donors are usually young, healthy women between 20 and 30 years old, which is the optimal egg-freezing time. The journal Human Reproduction published a comprehensive study in 2010 which looked at the success rates for 600 women who used donor eggs for IVF. The group was split into two randomly assigned groups, one using frozen and thawed donor eggs and half using fresh, recently retrieved donor eggs. The result “confirmed the effectiveness of egg freezing because there was no significant difference in the pregnancy rates between the two groups.

Then what factors affect egg freezing success rates?

So which success metric should we look at? Successful thawing rates, fertilisation rates, pregnancy rates, and live birth rates are ALL very different things. All of these data are useful but comparing apples with apples is important. Since the main goal of egg freezing is to result in a healthy baby, looking at live birth rates will do good, right?

Unfortunately it’s not that simple. Because how that number is calculated is also varied, the published numbers can have a huge range, anywhere from 2% to 40% or more. This is usually because they are measuring different things. The commonly cited 2% to 12% success rate often used to discredit egg freezing is per egg retrieved, using the older freezing methods. Using new, advanced vitrification, fast freezing, methods gives better numbers like 4% to 14% per egg retrieved. When you multiply those percentages by the number of eggs frozen, the picture starts to look a lot more promising.

Now let’s look at other variables which can make a huge difference in the live-birth success rates.

1. Age at time of egg freezing and number of eggs frozen

We can’t emphasise enough the importance of age. In short, the younger a woman is when she freezes her eggs, the higher the likelihood that using those eggs will result in pregnancy and live birth. Young women in their 20s are more likely to produce a larger number of higher quality eggs in a given egg freezing cycle and egg quality drops there after. So when it’s time to use the eggs, there are higher chances for success. No matter where a woman is in her reproductive years, the number of eggs frozen clearly affects the final chances of pregnancy, by virtue of simple math: more eggs = more opportunities, and the chance for doctors to choose the highest quality, strongest embryos to transfer. So how many eggs should you freeze? The medical journal Fertility and Sterility published research in September 2017 offering some indicative numbers:

• Women under 35: freezing 15 mature eggs offers a cumulative 80% chance of at least one live birth.
• Women 35 to 37: freezing 20 mature eggs offers a cumulative 80% chance of at least one live birth
• Women 38 to 40: freezing 30 mature eggs offers a cumulative 75% chance of at least one live birth.
• Women 40 to 42: freezing 30 mature eggs offers a cumulative 50% chance of at least one live birth.

2. Freezing methods and lab quality

One of the challenges when facing egg freezing success rates is that many reported studies are looking at women who froze their eggs with labs that used older, less effective technologies to freeze and store the eggs. The “slow freezing” technique was the standard until fairly recently, and because of the gap between when women freeze their eggs and when they use them, the data is usually several years or even a decade out of date. “Slow frozen eggs” have an average thawing survival rate of 61%, but eggs that were frozen using the “flash freezing”/vitrification technique do much better, with an average 90% to 95% rate of survival.

According to SCRC’s Chief Science Officer, Dr. Jason Barritt, “the most effective vitrification methods performed by the most experienced laboratories using cutting-edge technologies can now achieve closer to 100 percent survival with those surviving eggs likely being of higher quality.” Once the eggs are thawed successfully, how they are treated in the lab and the technology available for fertilising, culturing and incubating the resulting embryos can have an enormous impact on how those embryos fare after transfer and their implantation rates.

3. Number of embryos transferred

After freezing, thawing, fertilisation and culturing, the final hurdle to pregnancy is the embryo transfer and implantation. If everything has gone well up until this point, the doctor should have several embryos suitable to transfer. Transferring more than one embryo can increase the final live birth rate. Because of the risks inherent in multiple pregnancies, however, if the embryos are high quality, most experts will transfer a single embryo, or two at the most. Any leftover embryos can remain frozen for later use, offering another chances of pregnancy in the future.