Egg Freezing: Risks and Benefits
Oocyte cryopreservation has many potential benefits including improved efficiency of ART and as an alternative to embryo freezing for religious reasons and/or in compliance with certain legal statutes. Cryopreservation may lessen the severity of OHSS by avoiding embryo transfer in patients with excessive ovarian stimulation. Donor oocyte recipient patients may benefit, as would some in the treatment of congenital disorders or to prevent ovarian loss secondary to surgery, or chemotherapy/radiation. It may be a potential treatment of premature ovarian failure, where there is a significant familial component. While all of these potential indications are exciting and may give many patients great hope, oocyte cryopreservation should still be considered investigational in nature and only be done under the auspices of an Institutional Review Board (1) based upon many of the issues below.
Ethical dilemmas may arise when the desire to cryopreserve oocytes and preserve fertility may, by the very nature of the ART process to collect the oocytes, require the delay of a life-saving treatment (i.e. chemotherapy for leukemia). Therefore, if the process needed to collect oocytes could lead to unacceptable delay of therapy the procedure would be contra-indicated. Ovarian tissue cryopreservation has potential to obtain oocytes more quickly and thus allowing chemotherapy sooner, but only one pregnancy has reported to date in a patient that had orthotopic autotransplantation after chemotherapy for Hodgkin’s Lymphoma several years ago (2). Dudzinski (3) raised several important ethical issues with regard to oocyte cryopreservation in adolescents, and many of these also apply to adults. Clinicians must 1, insure the intervention does not harm the patient by delay of cancer treatment; 2, insure no remnant cancer cells will be re-introduced in transplantation or treatment;3, prevent damaged cryopreserved oocytes from being fertilized and implanted; 4, seek informed consent from patient and parents; 5, develop policies to protect the patient’s future rights to he gametes; 6, develop policies for deposition of gametes if the patient dies; and 7, respect the patient by protecting her from harm while also honoring her right to self-determination. Clearly, this technology has great potential and also great risk much like IVF did 30-40 years ago when the pioneers in the field were doing their seminal work leading to the birth of Louise Brown in 1978.
At present, the efficacy of oocyte cryopreservation is quite low, but is improving. Borini et al (2004) recently reported on their outcomes with 68 patients having cryopreserved 772 oocytes. 737 oocytes were thawed and 37% survived the thaw, with 124 fertilizing (45.4 %) and 13 children born. All were healthy with normal karyotypes. Boldt et al (5) reported on 2 series of patients, with and without sodium in the medium. The sodium rich media was used in 7 patients with 60 frozen oocytes. Only 12% of the oocytes survived the thaw and none conceived. Sodium depleted media was used with the next 16 patients that cryopreserved 90 oocytes. 74% of oocytes survived the thaw and 59 oocytes fertilized. There were 4 pregnancies from these 16 patients. There appears to be no increase in the rate of chromosome abnormalities in the fertilized oocytes (Cobo et al, 2001), though the yield of oocytes and ultimately embryos to transfer is quite low and seen with the reports by Borini et al (4) and Boldt et al (5). It is reassuring that the children conceived appear to be normal and had normal karyotypes. Winslow et al (7) reported on16 healthy babies born from 33 patients with 324 oocytes cryopreserved. One of the 16 had a ventricular septal defect, and the rest were normal. Porcu et al (8) reported on 13 children born from oocyte cryopreservation which were health as well. Oocyte cryopreservation with conventional cryopreservation protocols, even with modifications, seems to ultimately have lower pregnancy rates than FET or fresh IVF. Vitrification has been used in a small series of patients with good success. Yoon et al (9) had 7 patients with 217 eggs retrieved (29.7 +/- 5.8 eggs per patient, which seems like quite a lot!) where none conceived on their fresh cycle and had 90 oocytes left over for vitrification. 32 embryos were obtained from these vitrified oocytes and 3 of the 7 patients conceived. Possibly vitrification will be a better method and hopefully these results can be repeated by others.
In spite of a relatively few apparently normal babies conceived through oocyte cryopreservation, there are reasons to be cautious with this technology implementation. The mature oocyte is a very unique cell that can easily be damaged by the cryopreservation procedure. Intracellular ice may damage the plasma membrane and alter the function of membrane bound enzymes, permeability to water and cations, segregation of integral membrane proteins and affect gel phase transition (10). Microtubules are very sensitive to temperature depression where complete dissolution occurs at 0° C which will not be reconstituted upon re-warming in humans (10). It is damage to the meiotic spindle that is the most likely cause for the aneuploidy (i.e. abnormal numbers of chromosomes) seen with cryopreservation of oocytes. Mandelbaum et al (11) showed by confocal microscopy that the destabilization of the spindle was associated with a still compact metaphase plate when cryopreservation was done of mature oocytes. These types of studies elegantly show that the structures that are important for the chromosomes to separate are damages in the process of oocyte cryopreservation.
It is possible that some of the oocytes escape this damage and produce embryos with normal karyotypes (chromosome complement). The zona pellucida may become hardened and cortical granules are decreased which may be a factor in the decreased fertilization seen with thawed oocytes (10). Cytoplasmic organelles such as mitochondria are susceptible to damage (12), and skewed segregation of mitochondrial DNA mutations have been found in frozen, thawed and cultured oocytes (13). Additionally, oocyte DNA appears to be destroyed via apoptosis during cryopreservation and subsequent culture (14), which may also play a role in the overall poor recovery of normal oocytes and embryos. It is obvious that the mature oocyte is very sensitive to the cryopreservation procedure.
It seems that the renewed interest in oocyte cryopreservation will lead to more advances. If we can find some method to protect the microtubule apparatus, the efficacy will improve dramatically and oocyte cryopreservation’s full potential may be realized. There are clearly more unknowns at present. It is definitely experimental in nature and our patients need to understand this.
Is egg freezing a routine procedure? Is it ready for 'Prime Time?' Why aren't all IVF clinics doing the procedure? Patients must realize that the only way to obtain mature oocytes is from a "fresh" IVF cycle. Most pateints want to maximize their chances to conceive given the cost and stress associated with an IVF cycle. Pregnancy rates are generally twice as good using fresh as compared to frozen gametes and embryos. While a patient may have many mature eggs, they all have different potentials to fertilize and produce healthy embryos. When we fertilize all of the embryos and allow them to be grown out in culture, we can identify the abnormal ones, in general. Embryos that fail to grow well typically are chromosomally abnormal, much like we see in embryos that miscarry. Infact, about 50% of the embryos generated are abnormal. Therefore, many hope to grow the embryos to identify the ones that are normal and transfer only the normal ones. Thus, it is entirely possible that the eggs chosen to frozen could be abnormal. Possibly this is why the pregnancy rates are so low, in addition to all of the factors noted above. The American Society for Reproductive Medicine Practice Committee issues a Statement in 2007 (15) concerning the essential elements of informed consent for elective oocyte cryopreservation. They stress that the procedure is considered experimental and that only about 2 out of every 100 oocytes thawed result in a baby. Â This is consistent will the information presented above and encourages physicians to fully educate potential patients.
1. ASRM. Ovarian tissue and oocyte cryopreservation. Practice Committee. 2004. Fertil. Steril. 82(4):993-998.
2. Donnez J, Dolmans MM, Demylle D, Jadoul P, Pirard C, Squifflet J, Martinez-Madrid B, van Langendonckt A. Livebirth after orthotopic transplantation of cryopreserved ovarian tissue. Lancet 2004. Oct 16. 364(9443):1405-1410.
3. Dudzinski DM. Ethical issues in fertility preservation for adolescent cancer survivors: oocyte and ovarian tissue cryopreservation. 2004. J. Pediatr. Adol. Gynecol. 17(2)97-102. 4. Borini A, Bonu MA, Coticchio G, Bianchi V, Cattoli M, Flamigni C. Pregnancies and births after oocyte cryopreservation. 2004. Fertil. Steril. 82(3):601-605.
5. Boldt J, Cline D, McLaughlin D. Human oocyte cryopreservation as an adjunct to IVF-embryo transfer cycles. 2003. Hum. Reprod. 18(6):1250-55.
6. Cobo A, Rubio C, Gerli S, Ruiz A, Pellicar A, Remohi J. Use of fourescence in situ hybridization to assess the chromosomal status of embryos obtained from cryopreserved oocytes. 2002. Fertil. Steril. 75(2):354-60.
7. Winslow KL, Yang D, Blohm PL, Brown SE, Jossim P, Nguyen K. Oocyte cryopreservation/a three year follow up of sixteen births. 2001. Fertile. Steril. 76(3) Supplement 1; S120.
8. Porcu E, Fabbri R, Seracchioli R, De Cesare R, Guinchi S, Caracciolo D. Obstetric, perinatal outcome and follow-up of children conceived from cryopreserved oocytes. 2000. Fertil. Steril. 74(3):Supplement 1;S48
9. Yoon TK, Chung HM, Lim JM, Han SE, Ko JJ, Cha KY. Pregnancy and delivery of healthy infants developed from vitrified oocytes in a stimulated in vitro fertilization- embryo transfer program. 2000. Fertil. Steril. 74(1):180-182.
10. Parks JE. Hypothermia and mammalian gametes. In Reproductive Tissue Banking. Eds. Karow AM, Critser JK. 1997. Academic Press. San Diego. Pp 229-261.
11. Mandelbaum J, Anastasiou O, Levy R, Guerin JF, de Larouziere V, Antoine JM. Effects of cryopreservation on the meiotic spindle of human oocytes. 2004. Eur. J. Obstst. Gyn. Rep. Biol. 113S:S17-S23.
12. O’Connell M, McClure N, Lewis SE. The effects of cryopreservation on sperm morphology, motility and mitochondrial function. 2002. Hum. Rep. 17(3):704-709.
13. Blok RB, Gook DA, Thorburn DR, Dahl HH. Skewed segregation of the mtDNA nt 8993 (T →G) mutation in human oocytes, 1997. Am. J. Hum. Genet. 60(6):1495-501.
14. Men H, Monson RL, Parrish JJ, Rutlege JJ. Degeneration of cryopreserved bovine oocytes via apoptosis during subsequent culture. 2003. Cryobiology. 47: 73-81.
15. ASRM. Essential elements of informed
consent for elective oocyte cryopreservation: A Practice Committee
Opinion. 2007. Fertility and Sterility. 88(6): 1495-1496.