Cryopreservation of gametes (sperm and oocytes) and embryos has been an essential component of assisted reproductive technology (ART) for many years. Cryopreservation of semen, first employed successfully in the 1950s, has potentiated safe intrauterine insemination, effectively eliminating transmission of sexually transmitted disease with current practices of quarantining and retesting before use. It has also been effectively utilized for fertility preservation for men facing surgery, chemotherapy or radiation for malignancy likely to render them sterile, and prior to vasectomy. Embryo cryopreservation, successfully first performed in the 1980s, offered an option for storage and successful subsequent use of supernumerary embryos created with in vitro fertilization (IVF). It is now relied on for patients having a host of genetic tests performed on their embryos to allow time to receive results before transfer, for women seeking fertility preservation for a variety of reasons and other women that have temporary or permanent contraindications to proceeding with fresh embryo transfer or pregnancy.
More recently, it has been appreciated that frozen embryo transfers often produce higher success rates than fresh cycles and result in safer pregnancies for mothers and babies. These advantages include a lower incidence of preterm deliveries and small for gestational age neonates. Cryopreservation of oocytes developed in the late 1990s has potentiated fertility preservation for women for the same indications used for sperm freezing. In addition, the well-recognized age-related decline in fertility in women, attributed to diminishing oocyte quantity and quality, has created new and exponential demand for fertility preservation for so-called “social” reasons. Successful cryopreservation of oocytes has been the most technically challenging process but survival rates greater than 90% have now been reported.1
The success of these technologies has rapidly led to a very large inventory of cryopreserved tissues around the world. Many couples and individuals electing to cryopreserve gametes and embryos have an indefinite time horizon for their use, which adds to the challenge of storing large quantities of tissue over long periods. For the most part, fertility clinics have admirably met this challenge.
One of the highest priorities of a fertility clinic and its laboratory is to safeguard any cryopreserved reproductive tissue (e.g. sperm, eggs, and embryos) in storage at the clinic. Such storage requires the highest level of surveillance to maintain appropriate cryogenic conditions and immediate reaction and action when conditions do not meet the needed standards. In many cases, reproductive tissues are irreplaceable and may represent the only opportunity for future offspring for the affected patient.
Cryopreservation with all of these techniques is a safe, reliable methodology that has generally been taken for granted by patients and health care professionals. However, cryopreservation of human tissue is subject to two primary problems: microbial contamination (not addressed in this commentary) and failure of the requisite equipment to maintain cryogenic conditions. Recent well-publicized simultaneous failures of cryogenic storage tanks at two American fertility centers earlier this year created considerable alarm throughout the industry after thousands of cryopreserved sperm, egg, and embryo specimens were placed at risk. Cryogenic storage tank failure occurs when either the cryogenic storage tank’s temperature is inadequate for storage of reproductive tissue or the volume of cryoprotectant (liquid nitrogen, LN2) required to maintain the cryogenic storage tank is insufficient. As a result of either of these conditions, the reproductive tissue may completely or partially thaw, causing irreversible damage or even destruction of the reproductive tissue.
These recent events have received extensive coverage and created legitimate concerns regarding the safety and reliability of cryopreservation systems. The following information is intended to address concerns and queries regarding the processes, management, and maintenance of systems associated with reproductive tissue cryopreservation and storage.
The authors report no potential conflicts of interest with regard to this article.
- Crawford,S., Boulet, S.L., Kawwass, J.F., Jamieson, D.J., Kissin, D.M., 2017. Cryopreserved oocyte versus fresh oocyte assisted reproductive technology cycles, United States. Fertil Steril. 2013;107:110-118.
- Szell AZ, Bierbaum RC, Hazelrigg WB, Chetkowski RJ. Live births from cryopreserved human semen stored for 40 years. J Assist Reprod Genet. 2013;30(6):743-744.
- Dowling-Lacey D, Mayer JF, Jones E, Bocca S, Stadtmauer L, Oehninger S. Live birth from a frozen-thawed pronuclear stage embryo almost 20 years after its cryopreservation. Fertil Steril. 2011;95:1120.e1-1120.e3.
- Tomlinson M, Morroll D.. Risks associated with cryopreservation: a survey of assisted conception units in the UK and Ireland. Hum Fertil. (Camb) 2008;11:33-42.
- Standards and technical manual reproductive cells and tissues. American Association of Tissue Banks, 2002.