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Does Number of Frozen Embryos Correlate with IVF Success?

In a recent retrospective cohort study, researchers at Weill Cornell Medical College looked at data of all patients undergoing a fresh IVF cycle and a subsequent frozen IVF cycle over a 13-year period. They sought to determine whether there are any predictors of the likelihood of success in a frozen embryo transfer after failure to conceive in a fresh embryo transfer.

Patients under the age of 35 were broken out into two groups:

  • Group one patients had a negative pregnancy test on the fresh cycle; a negative pregnancy test on the frozen cycle
  • Group two patients had a negative pregnancy test on the fresh cycle; a positive pregnancy test on the frozen cycle
  • Group two patients had more eggs, a greater number of eggs fertilize and more embryos frozen than Group one patients

“What they found was that for younger patients, specifically women under 35, the more eggs they had retrieved in their fresh cycle, and the more embryos they had frozen, the higher the success rate even though they were transferring the same number of embryos,” says Dr. Owen Davis, a fertility doctor at The Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine at Weill Cornell Medical Center.

Researchers developed an odds ratio that translated to approximately a 20% increase in success rates in Group two. “To put that in perspective, if you would expect a 50% live birth rate for people under 35 doing frozen embryo transfer, and it’s 20% better in one group, it would be 50% versus 60%,” Davis explains.

“That in and of itself is not intuitively all that surprising,” Davis says. “An argument could be made that some women make more eggs and more embryos, and to some extent that is really saying they have better embryo reserve and better ovarian functioning. That simply predicts they are more likely to succeed, even in you put back in the same number of embryos.”

What Davis did find surprising about the data is that the same thing didn’t hold true for women over 35. It could be the vagaries of statistics or a real cause and effect, he says. The older patients, women over 40 are less likely to have embryos to freeze, so you may not have meaningful enough numbers to make the same conclusions.

The researchers concluded that patients under 35 with fewer frozen embryos should consider undergoing another fresh cycle prior to doing a frozen cycle. “I wouldn’t say that would necessarily be my conclusion,” Davis says.

Success rates of 60% versus 50%, wouldn’t prevent Davis from doing a frozen embryo transfer for the person with fewer embryos, he said. But the data may be useful for counseling purposes. “Patients who have frozen embryos typically will want to transfer them, unless it’s someone who wants a very large family. Lets say you have two frozen, you have no children, you want to have three kids if you could, and you’re 39. You might want to go through a fresh cycle to keep a few frozen, so when you’re older you’ve got the backup. But that would be less the case in someone who’s under 35.”


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