Improving IVF Success Rates Through Embryo Freezing
Reproductive endocrinologists are in a continuous search for techniques that improve IVF success rates. Since the earliest days of IVF, controlled stimulation of the ovaries has been the standard of care. The reason for stimulation is to obtain multiple mature eggs for either insemination or direct injection of sperm into the egg. Conventional wisdom has long held that removing multiple eggs results in the formation of multiple embryos each of which has different potential to result in a live birth. Since all women have a significant percentage of genetically abnormal eggs, having multiple eggs to work with increases the possibility that one or more genetically normal, high quality embryos will be available for transfer to the uterus. Ultimately the success rate of an IVF treatment cycle is improved if there are several embryos to choose from. In addition, depending on the age of the patient, transferring more than one embryo to the uterus usually results in improved ongoing pregnancy and live birth rates.
However, stimulating the ovaries to produce multiple eggs is not without detrimental effects. For example, estrogen levels during the stimulated cycle are usually extremely high, sometimes reaching 10-15 times normal levels. In addition progesterone levels may be decreased due to removal of the ovarian cells responsible for the production of progesterone. Progesterone may further be reduced by the use of medications (gnRH agonists and antagonists) that are required to prevent early ovulation during the stimulation phase of the cycle. During the fresh IVF treatment cycle, removal of eggs by insertion of a needle into the pelvis causes some inflammation and a small amount of bleeding, both of which may be detrimental to the normal process of embryo implantation.
Transferring frozen/thawed embryos in a completely separate cycle would eliminate the adverse effects discussed earlier, and has potential to significantly improve live birth rates. There is support for what is often termed “freeze all” in certain situations at this time and the concept seems to be gaining momentum. It is imperative that any program considering freezing all embryos for future transfer in a non-stimulated cycle has a very successful embryo-freezing program. Recent research has suggested that “freeze all” may be advantageous for patients who are high responders to stimulating medications, low responders, and patients with known endometriosis. Additionally, if progesterone levels are elevated above a certain threshold at the time that the trigger shot is scheduled to be given, “freeze all” is the best option. It may be that the indications for “freeze all” will continue to broaden as freezing methods continue to improve and more research is done.