Social egg freezing is a big topic of conversation in our office these days. My colleague Nicole Ellis has launched a video docuseries about her journey to figure out whether she should use the technology to save eggs that she could potentially use to fertilize later, when she feels the time is right. ("Social" differentiates this reason for egg storage from, say, freezing eggs before cancer treatment or for other medical reasons.) A number of other 20- and 30-something reporters, editors, producers and others are thinking about the procedure, too.

Egg-freezing technology has undergone huge changes in recent years. A new flash-freezing process known as vitrification has bumped up success rates and pushed down costs. A growing number of companies — following in the footsteps of Facebook and other Silicon Valley firms — are now covering part or all of the cost as part of their employee health benefits. A survey released earlier this year by advisory firm Willis Towers Watson of 400 companies representing 7 million employees found that 66 percent of the employers expected to offer fertility benefits by 2019 as compared with 55 percent in 2017. This perk sometimes includes up to $10,000 or $20,000 of costs.

But for all the buzz about social egg freezing, there's very little hard data available in the United States about who is using it, how they're using it and whether it is working out for them.

This week, many of the world's fertility experts are meeting in Barcelona for the European Society of Human Reproduction and Embryology. This meeting is important because a number of countries represented at the gathering track egg freezing and other procedures more closely than the United States does. Data from the Brussels Center for Reproductive Medicine released Wednesday by researcher Michel De Vos reveals a fascinating picture of the women choosing to freeze their eggs for social reasons. The Brussels Center is one of Europe's largest fertility clinics.

The research looked at 563 women — with a median age of 36.5 years — who underwent 902 procedures to collect their eggs from January 2009 to November 2017. The cycles resulted in a mean of 8.5 eggs retrieved and frozen.

So far, only 7.6 percent or 43 have returned to have their eggs thawed, fertilized and transferred. This probably reflects the fact that some of the women froze their eggs only recently. The mean age of people returning to use their eggs was 42 years.

The researchers noted that the thawed eggs had a high survival rate of 73.4 percent. The pregnancy rate was 32.6 percent after embryo transfer or 14 of 43 — which really hits home the point that egg freezing is not a guarantee of a baby.

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