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Discusses Women's Health

As women spend more and more years achieving education, establishing and advancing their careers, and taking time (and often multiple relationships) to find the right partner, they are likely to postpone having children. And if this is not a personal issue, it might be for your daughters. We’ve heard a lot about the issue of delayed fertility and the possibility of egg freezing. I have written about it in a previous website article. There was an excellent article on the subject published in this week’s New England Journal of Medicine and I thought I would share some of the principal points…

All of a woman’s eggs (oocytes) develop in the ovaries during the embryonic stage. Unlike sperm in the testes, none are created thereafter! At birth, we have millions of these primordial oocytes. They then proceed to undergo massive atresia (a medical word for death) during infancy and childhood and by the time we hit puberty we have only 400,000 left. Thousands continue to die each month during our reproductive years, and many that remain undergo the stress of aging and chromosomal destruction and by the time we reach our early 40s we are left with the “rejects” i.e. eggs that are less likely able to undergo successful fertilization and development of a viable, healthy embryo.

There are certain factors that are associated with an accelerated decrease in the number of eggs and diminished fertility at a relatively early age. These include a family history of early menopause, genetic factors, smoking, ovarian surgery, pelvic radiation and the use of chemotherapeutic agents. The freezing of oocytes is therefore a good option for women who wish to have children in the future but have had any of these factors which impact their ability to do so. It’s also reasonable to consider freezing eggs in order to be able to donate them or to save “extra eggs” that were not initially used during an in vitro fertilization cycle. (The fertility drugs used to stimulate development of the eggs may cause too many to be used in one IVF cycle and hence some will be saved for another time or can possibly be donated.) The question is whether egg freezing should be done to preserve fertility in order to delay pregnancy for personal reasons.

In order to make that decision, physicians should counsel patients about the process of oocyte cryopreservation and the chance of success… The oocyte is fairly large and has a high water content, hence when it’s frozen there is a chance for ice crystals to form causing cell injury or death during the freezing process. The current freezing techniques use cryoprotectants to remove water from the cell and reduce the formation of ice crystals. Once the egg has been exposed to the cryoprotectants, it is vitrified (which basically means it’s very quickly frozen) and may then be stored for years. Then before used for IVF, the vitrified eggs are rehydrated in a warming solution. The American Society for Reproductive Medicine recommends that sperm be directly injected into the cryopreserved egg (ICSI) because there are alterations in the outer layer of the egg during this procedure. To harvest and retrieve the eggs used for cryopreservation (this is sounding so agricultural), ovarian stimulation is performed with fertility drugs which takes up to two weeks. The oocytes and surrounding fluid are then aspirated through a needle placed through the vagina under ultrasound guidance. (Done with mild sedation.)

The success of using these cryopreserved eggs is dependent on their age at the time they were harvested. Studies have shown that the proportion of vitrified oocytes that resulted in a live birth was 8.2% in women 30 to 36 years of age and 3.3% in women older than 36 to 39 years of age.

Another study has shown that outcomes for live birth rate decreased by 7% for every year of increase in the age of the woman when the oocytes were frozen. The good news is that available data on births resulting from previously frozen eggs as compared with fresh eggs have not shown an increased risk of congenital anomalies among the offspring. (However, there have been less than 2000 births resulting from cryopreserved oocytes reported in the literature.)

Based on these numbers, the author suggests that the most appropriate age for effective cryopreservation of oocytes would be in the early to mid 30s before the age at which a woman’s fertility naturally declines. But a woman also has to be informed of the cost, the time, the lack of assurance of success, the medications and the risks involved with the procedure. The latter include ovarian hyperstimulation syndrome which can cause swelling of the ovaries, excess fluid in the abdomen, and in rare conditions, infection and internal bleeding.

The guidelines of the American Society for Reproductive Medicine recommend caution regarding the use of vitrification to circumvent the effects of aging on the reproductive potential of healthy women. They specifically state that ” … there are no data to support the safety, efficacy, ethics, emotional risk and cost effectiveness of oocyte cryopreservation for this indication.”

What I tell my patients is that they need to understand the potential success and failure rates and that they differ among clinics because of variations in freezing and warming techniques. If they do decide to undertake cryopreservation of their eggs, they should be seen at a fertility clinic with expertise in cryopreservation and request the statistics for success of this procedure in their age group. Who said this was easy?

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