MONTREAL — Women who freeze their eggs at age 33 hoping to pause their biological clocks until they are ready to conceive at age 42 are actually no better off than if they simply underwent a fresh IVF cycle—if necessary—at age 42, according to new research.
The first metaanalysis of oocyte cryopreservation success rates shows the technique is 4–5 times less efficient than standard in vitro fertilization with fresh oocytes, reported Kutluk Oktay, M.D., of Cornell University, New York.
“I think the current success rates with oocyte freezing justify its use when a medical indication exists, but the same cannot be said for elective freezing at the present time,” Dr. Oktay said in an interview.
A total of 118 babies worldwide have been born from frozen oocytes—97 from the slow-freeze technique and 11 from vitrification techniques, he said at the joint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society. Previous estimates of about 180 frozen-egg births might have been confused by overlapping reports in the literature, he explained.
The metaanalysis included 30 reports in peer-reviewed journals—26 detailing slow-freeze techniques and 4 detailing vitrification. The live birth rate per thawed oocyte is 1.9% for slow freeze and 2% for vitrification.
Dr. Oktay compared data from the 118 frozen egg pregnancies (from 397 thaw cycles) with data from a control group of 397 fresh intracytoplasmic sperm injection (ICSI) transfer cycles at his institution. Women who had cycles involving frozen eggs had a mean age of 33; those who had ICSI cycles had a mean age of 33.6.
When assessing the number of live births per injected oocyte, the rates in the frozen egg cycles were 3.4% (slow freeze) and 4.5% (vitrification), compared with 6.6% in fresh IVF/ICSI and 7.5% with the addition of subsequent frozen-embryo transfers.
There are insufficient data to assess the vitrification method, he said, but compared with slow-freeze oocyte cycles, fresh IVF plus subsequent frozen embryo cycles had an implantation rate per transferred embryo almost four times higher (36.9% vs. 12.8%; odds ratio 3.68).
Similarly, live births per transfer were significantly higher (OR 3.58) in the fresh-IVF/frozen-embryo cycles (50%) compared with slow-freeze oocyte cycles (21.6%).
Egg freezing in women aged 33 has success rates comparable with those achieved using fresh IVF in women aged 41 and 42 years, he concluded.
“We cannot recommend this strategy for routine clinical use, since we do not have an accurate assessment for risk/benefit,” he said. “When ovarian failure is highly likely as a result of medical treatments, this is an easy decision. When dealing with reproductive aging, the data are not there yet.”