With egg freezing being touted as a way for women to potentially expand future childbearing options, the viability of those eggs when they're defrosted is still relatively unknown. The latest bit of guardedly good news is a short report in JAMA indicating that frozen eggs do indeed lead to live births after IVF nearly half the time — but that the odds of a live birth are almost 20 percent higher for IVF using fresh eggs.
The report, by Vitaly Kushnir and his colleagues at the Center for Human Reproduction in New York, is based on a retrospective analysis of success rates that U.S. fertility clinics send to the Society for Assisted Reproductive Technology. In 2013, donated eggs (as opposed to eggs from the would-be mother herself) were used in 11,148 IVF cycles. Most were fertilized and implanted as soon as they were retrieved, while 20 percent had been frozen after donation and were then thawed and fertilized. Kushnir and his colleagues looked at IVF success rates in terms of eventual live births and compared the rates for those using fresh donor eggs with those using frozen donor eggs.
The live birthrates per embryo transferred were 56.1 percent for embryos made with fresh donor eggs and 47.1 percent for those made with frozen donor eggs. In other words, a live birth was 19.1 percent more likely using fresh donor eggs rather than frozen.
It's hard to say what might account for this difference, Kushnir said. "The quality of the eggs could be somehow diminished by freezing and thawing." Or it could be explained by the fact that women who use frozen donor eggs get fewer eggs altogether, since they're split among a couple of recipients — and fewer eggs means fewer potential embryos.
In most clinics, a woman who uses a donor gets all the fresh eggs the donor produces — which, according to Dr. James Toner, president of SART, is usually about 15 to 20 mature eggs. But if she has to turn to frozen eggs from the egg bank, which he said are typically sold in batches of about half a dozen, she will usually have to share that batch with another woman.