MONTREAL — Preliminary results from an ongoing study of oocyte cryopreservation show “the highest pregnancy rates so far reported,” making egg freezing “a viable clinical option,” according to Dr. John K. Jain, the principal investigator.
“Egg freezing has turned a corner—it's arrived,” said Dr. Jain, of USC Fertility, the nonprofit fertility practice of the University of Southern California's Keck School of Medicine, Los Angeles.
A total of 20 women (mean age 31 years) have been enrolled in the study, which provides them with in vitro fertilization at no charge. To date, five of eight women have become pregnant after having their eggs removed and frozen for 1 month, then thawed and fertilized by intracytoplasmic sperm injection, followed by subsequent embryo transfer.
He reported the findings in a poster at the joint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society.
A recent metaanalysis of all published frozen-egg pregnancies (118) suggests a worldwide live birth rate of 21.6% per transfer in women with a mean age of 33 years, reported Dr. Kutluk Oktay in a separate presentation at the meeting (see accompanying story). Unpublished data from the World Congress on Human Oocyte Cryopreservation suggest that the highest U.S. success rate until now has been a 34% pregnancy rate per transfer at Assisted Fertility Services of the Community Health Network in Indianapolis.
Dr. Jain attributes the success of his egg freezing protocol to a combination of culture medium and freezing method. The center uses a slow-freeze protocol in sodium-depleted, choline-substituted medium.
Two of the five women have delivered singletons, with the other pregnancies (including a set of triplets) well into their second or third trimesters, he said.
Each transfer procedure included an average of 3.2 embryos, compared with an average of 2.7 embryos per transfer reported in the egg freezing metaanalysis.
The American Society for Reproductive Medicine currently recommends that in women younger than 35, no more than two embryos should be transferred; it also recommends that consideration be given to single embryo transfer in patients with the best prognosis.
The optimal number of embryos to transfer following oocyte cryopreservation is still undetermined, Dr. Jain said.