The primary reason why this has become a viable option is that the technology of freezing oocytes has advanced greatly. Although the debate still continues about which of two freezing methods is best, presently vitrification of oocytes seems to be winning the race. The problem with freezing egg, sperm or embryos is that as they freeze, the intracellular water makes ice crystals. Thawing then ruptures the cells. For embryos, the problem was solved by using. Combining these cryoprotectants with a slow freeze and programmed thaw prevented the ice crystals form forming. The oocyte was different in that the above-described technologies damaged the metaphase-II (MII) oocyte due to its large size and higher water content. Newer protocols using the slow freeze, in some clinic’s hands, are much improved, but another process (with even better success) has come onto the scene.
Vitrification freezes oocytes rapidly causing the cellular water to perform more like a glass, which prevents crystal formation. A recent meta-analysis suggested that there was little difference between the two methods in creating viable oocytes. However, the only prospective randomized trial demonstrated a clear superiority for vitrification. Whatever procedure is used, clinical pregnancy rates have improved to the point where, oocyte – for –oocyte, frozen oocytes are a successful as fresh oocytes. Thus, new technology has made freezing eggs a reasonable clinical option.
The pregnancy rates for frozen oocytes rival that of fresh oocytes. But there are very important limits to this knowledge. For one thing, not many patients have had this done. Another point is that the data is largely for younger women. Finally, many of the oocytes that have been frozen will not be used for years – if ever- so a realistic pregnancy rate is currently not accurate. In a large prospective randomized trial conducted by Gary D. Smith (Fertil. Steril 2010; 94; 2088), the authors report a 38% clinical pregnancy rate using oocytes frozen using vitrification. Expressed as a clinical pregnancy rate per oocytes, the value is 5.2%. Rienzi et al (Hum Reprod 2012: 6; 1612) reported that as with all forms of female fertility, success was age dependent.
That having been said, oocyte freezing can benefit oncology patients who need to undergo gonadotoxic chemotherapy. Other indications include freezing for oocyte donation programs and to reduce the risk of ovarian hyperstimulation syndrome for patients undergoing gonadotropin stimulation. The usage that is gaining interest in the press, however, is the non-medically indicated, elective freezing of oocytes for fertility preservation for women who are aging, but not ready to be pregnant. Undoubtedly, women are delaying childbearing. Unfortunately, there is no accurate test to determine when a woman’s fertility will decline to the point where she no longer has oocytes competent to result in the birth of a child.
Enter oocyte freezing. But if the ideal candidate for oocyte freezing is a younger woman, and many of them feel they can still become pregnant , why freeze oocytes? Great question! The only reason to consider freezing oocytes is as an insurance policy to reserve fertility as a woman ages. Many who choose to do this will never utilize their oocytes. But for those who do need them at a later date, oocyte freezing offers an option- not a certainty – for potential children. Unfortunately, if a woman has already reached an age when her oocytes are not viable (meaning she may get pregnant now), freezing eggs at this stage does not improve her chances of getting pregnant later.
First and foremost, oocyte freezing is new technology and no one can predict where the demons may lie. But that is true of all assisted reproductive technologies, considering that the oldest IVF person is still in her late 30s. In addition, the procedures to retrieve and freeze the eggs are expensive, and frozen eggs incur a yearly fee for storage. Finally, the procedure itself carries small, but finite, risks such as bleeding or infection from the oocyte retrieval, and the stimulation process is rigorous and time consuming.
“Doctor”, my patients ask, “what would you do?” I can best answer this question by employing the yardstick often used by physicians regardless of their specialty. If my daughter were to ask me about doing this, and she was properly informed and met the indication criteria for using this technology, then I would encourage her to take advantage of the technology. Guarded? Yes, but none the less an endorsement for freezing oocytes.