While the trend for older motherhood continues, amidst the warnings of the experts on the sharp drop in a woman's fertility in her mid-30s, more and more women consider egg freezing as a form of "insurance" against age-related infertility.
Recent data released by the Human Fertilization and Embryology Authority (HFEA) confirmed that freezing eggs is the fastest growing form of fertility treatment in the UK, with a 10% increase in the last year.
But what happens when women want to go back to the clinic to use frozen eggs to create families? Our latest research reveals for the first time what percentage of them return to this "safety net" and what percentage can become mothers.
We analyzed data from two of the largest fertility clinics in London. We included information on all the women who had frozen their eggs and all those who had returned to using their eggs to attempt conception between 2008 and 2017.
During this ten-year period, 129 women – about a fifth of all women who had frozen eggs in the clinic – returned to using them. Of these women, just over a third (36%) had originally frozen eggs for so-called "social" reasons (due, for example, to concern over reproductive aging). The remaining two-thirds (64%) had frozen eggs for a variety of clinical reasons (as part of their "serial" in vitro fertilization or because no sperm sample was available on the day of egg collection) .
The overall success rate was 21%, which means that only one in five women who used frozen eggs ended up becoming a mother with those eggs. For social egg freezers, this figure was even lower, at 17%. But it is important to note that a further 26% of those who had tried but had not been successful until then, still had eggs or embryos remaining in stock, which, hopefully, could cause births in the future.
The age of women who frozen eggs ranged from 25 to 45, with an average of 37 years. Almost all (98%) of women who had frozen eggs for social reasons were single at the time of egg freezing. They returned to the clinic to thaw their eggs after about five years, with an average age of 43 years.
Although most women who freeze eggs for social reasons state that their main motivation is the desire to "buy time" to find a partner with whom to have a family, almost half of the women were still single when they returned to use the eggs. As a result, 48% used donor sperm to fertilize their eggs, choosing to pursue solo motherhood instead of waiting longer to find a partner.
As Ali, whose twins Molly and Monty were conceived using her frozen eggs and donor sperm, he explained, initially froze her eggs because she hoped she could find someone to have a family with. But over the years, she said:
I started considering solo motherhood. I thought I would be a good mom and I knew that if I didn't try to get the kids to do my frozen eggs, then I'd always regret it. I will always be grateful to the donor for giving me my children.
Ali's story is moving, especially when you see his beautiful five-year-old twins. But it is also a story of maternity against the odds.
With current success rates, most women who freeze eggs will not be as lucky as Ali because freezing the eggs offers no guarantee. Both the number of frozen eggs and the age of the woman when she frozen them are factors that influence the probability of success, but it is also – as with all fertility treatments – an element of the case.
Most women who have frozen eggs have not yet tried to use them. It is likely that many will conceive of the natural way, without ever having to go back to the clinic. Others may change their mind about having children or, for whatever reason, decide to discard the eggs without using them. But some will simply be waiting for the right circumstances.
In the UK, eggs frozen for social reasons can be kept for up to ten years (those for medical reasons can do so for up to 55 years), so we will not have conclusive data on what decisions women make after egg freezing until their storage period has expired. It is likely that more women, especially those who have frozen eggs in recent years, will try to use them in the future. As more and more women return to clinics, more extensive studies can and must be conducted, but until then our data provide the most complete view available and should be used to help women make more informed decisions.
Ali notes that, although she thinks the egg freeze gave her "an incredible opportunity", she didn't realize how hard it would be to conceive until she came back to use her eggs. "It took all the 27 eggs I had frozen to have my twins, so it was a close encounter," he says. "I was almost starting to panic!"
While I know that freezing eggs can be a positive option for some women and I firmly believe that all women should be supported in making reproductive choices that best suit them, I think we need to be clearer about the real likelihood that this technology leads to future motherhood.