At Southern California Reproductive Center, a little over a third of our IVF patients have spare embryos that are suitable for cryopreservation. Should the patient fail to conceive after transfer of fresh embryos, some or all of the remaining frozen embryos can be thawed and transferred on a subsequent attempt at conception or for expansion of the family if the fresh embryo transfer cycle had resulted in a birth. For various reasons, however, embryos may remain frozen long after a birth from their fresh, “sibling” embryos.  The question then becomes, “how long can these spare embryos remain frozen and still be viable enough to establish a healthy pregnancy”?

In theory, human embryos – frozen at anywhere from the “just-fertilized”, or zygote stage through the hatching blastocyst stage can remain frozen indefinitely. Once embryos have gone through the cryopreservation process and maintained in storage containers under liquid nitrogen conditions, there is essentially no biological or physiological activity that occurs in until they are thawed.  It used to be that births from frozen embryos that had been stored for over 8 years made headlines, but reports of births from embryos stored 10 years or longer aren’t considered “reportable” events now.

For many years, pregnancy rates resulting from thawed embryo transfers at SCRC have been close to what it is for fresh embryo transfers.  This is quite something, when one considers it wasn’t so long ago when worldwide pregnancy rates from thawed embryos was about one percent!  The slight reduction in per-embryo implantation rates when comparing thawed to fresh embryos is likely due to damage to the embryo’s cells during the freezing or thawing processes themselves, rather than from any injury caused by cryostorage per se. 

Thus, frozen embryo technology significantly increases the likelihood of pregnancy per IVF cycle, making IVF by far the most successful and efficient form of assisted reproductive technology – dollar-for-dollar – that is currently available to patients. The Success rates of SCRC clinicians are available on the web at www.sart.org.  Once there, click Patient Information, then IVF Success Rate Reports, then enter the 90210 zip code.  This should take you to Southern California Reproductive Center.

And as a final topic, what about identification of stored, frozen embryos – how can patients be sure they are getting their frozen embryos and not those from someone else? At SCRC, unambiguous, indelible identification techniques have been worked out over many years of successful cryobanking of gametes and embryos.  Many cross-checks exist within the system, reducing the possibility of an identification error to an absolute minimum.