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How Has Vitrification Improved Egg and Embryo Cryopreservation?

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July 22, 2014

With continual refinement of reproductive technologies, egg freezing is becoming more widely used for a variety of reasons, related to fertility preservation and in vitro fertilization (IVF).

For decades, fertility clinics utilized a slow freeze technique for cryopreservation (freezing of eggs and embryos). This method was successful with embryos, but frozen eggs showed only a 50% survival rate. It was clear that a more efficient and successful technique was needed. Today, vitrification allows for 90% or greater survival for both embryos and eggs. There is little to no ice crystal formation during freezing, thus making the thawing process more efficacious. The quality of the eggs and skill of the lab are largely influential on the survival or fertilization outcomes of these embryos or eggs.

Richard Paulson, M.D., Director of USC Fertility in Southern California explains that vitrification has significantly improved methods of cryopreservation and continues to improve as research findings emerge. “With vitrification, a higher proportion of eggs will survive giving the patient additional chances at pregnancy. It used to be that it took two eggs to make one embryo (with slow freeze) and each egg had 15% chance of becoming an embryo. Now with vitrification, it is more like 20% chance. There is greater efficiency.” Vitrification increases the probability that you may get a baby out of each egg.

Zsolt Peter Nagy, Ph.D., Lab Director and Embryologist with Reproductive Biology Associates in Atlanta, Georgia says that vitrification has also made it possible for patients to have a greater number of options regarding fertility preservation or treatment. “Most IVF clinics and RE (Reproductive Endrocrinology) physicians always try to obtain the most eggs from each stimulation cycle to maximize efficiency. The more mature eggs you obtain, the more options the patient has, independently of what the objective is (to inseminate the eggs or to freeze the eggs),” he says.

Nagy explains how vitrification has opened up options for women looking to delay childbearing, patients with medical conditions like cancer, and traditional IVF patients: “Today [fertility preservation] patients can choose to cryopreserve their eggs instead of cryopreserving embryos. In the past, the best (most successful) option was to cryopreserve embryos, but now egg cryopreservation provides similar outcomes.” Fertility preservation patients who do not currently have a partner do not have to feel forced into using donor sperm for creating embryos as freezing and thawing of unfertilized eggs is just as successful. Similarly, traditional IVF patients can now opt to fertilize only a portion of the eggs retrieved, eliminating the moral dilemma of what to do with unused embryos. IVF patients can also choose to freeze their eggs at the time of retrieval (for example if their partner is not available to provide sperm for embryo fertilization, if they are suffering from Ovarian Hyperstimulation Syndrome, or to allow the uterine lining to recover from the harsh effects of fertility drugs). Those vitrified eggs can be thawed at a later date rather than cancelling the cycle.

“Vitrification is an important step in the progress of cryopreservation techniques. It increases the chance of survival of the eggs and the chance of having a successful pregnancy from those eggs,” states Paulson.

Patients considering vitrification should choose a clinic that is skilled in both handling and storage of eggs and embryos. Though there is not a sufficient amount of latitudinal (long term) research available on the outcomes of vitrification cycles, patients may be able to do their own homework before making decisions about their treatment. “The technology is still emerging and not yet perfected,” Paulson says. Consult with several clinics and be prepared to ask questions. Your fertility doctor should be able to tell you approximately how many vitrification cycles have been performed at the clinic, approximately how many thaw cycles have been performed, the survival rate of eggs and embryos upon thaw, whether vitrification or slow freeze is practiced routinely at the clinic, and how many years they have been using vitrification techniques (if applicable).

Fertility doctors are always striving for the best outcomes for their patients. By refining vitrification techniques, more options with greater success will be available to patients over time.


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