Does oocyte cryopreservation have a future in Hungary?

Cryopreservation of embryos and oocytes in human assisted reproduction

Both sperm and embryo cryopreservation have become routine procedures in human assisted reproduction and oocyte cryopreservation is being introduced into clinical practice and is getting more and more widely used. Embryo cryopreservation has decreased the number of fresh embryo transfers and maximized the effectiveness of the IVF cycle. The data shows that women who had transfers of fresh and frozen embryos obtained 8% additional births by using their cryopreserved embryos. Oocyte cryopreservation offers more advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation, and postponing childbirth, and eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In this review, the basic principles, methodology, and practical experiences as well as safety and other aspects concerning slow cooling and ultrarapid cooling (vitrification) of human embryos and oocytes are summarized.

Over 900 oocyte cryopreservation babies born with no apparent increase in congenital anomalies

Over the past decade, the number of reported live births resulting from oocyte cryopreservation has rapidly increased. To appreciate the true number of children born, verified live births were tabulated and assessed. A literature search was performed; authors were then contacted to verify birth outcomes and provide updates. A database including all verified live born infants was constructed. A total of 58 reports (1986-2008) were reviewed, which included 609 live born babies (308 from slow freezing, 289 from vitrification and 12 from both methods). Additionally, 327 other live births were verified. Of the total 936 live borns, 1.3% (12) were noted to have birth anomalies: three ventricular septal defects, one choanal and one biliary atresia, one Rubinstein-Taybi syndrome, one Arnold-Chiari syndrome, one cleft palate, three clubfoot and one skin haemangioma. Compared with congenital anomalies occurring in naturally conceived infants, no difference was noted. With more live born data accumulating, this procedure may become mainstream as a fertility preservation option, particularly for women diagnosed with malignancy requiring cytotoxic therapy. A registry would help to assure the safest, most expeditious development of this technology.

Human oocyte cryopreservation in infertility and oncology

PURPOSE OF REVIEW

To evaluate the present state of research and clinical application of human oocyte cryopreservation in infertility and oncology.

RECENT FINDINGS

Recent literature documents have an increasing interest in cryopreserving human eggs. A number of studies report on different freezing protocols and various types of clinical application. Increasing attention is paid to vitrification as an alternative to slow cooling for oocyte cryopreservation. Several studies cover the modification of meiotic spindle during cryopreservation in order to assess the less damaging cryopreservation system. The first births with cryopreserved oocytes in cancer patients are reported.

SUMMARY

Egg freezing may circumvent the ethical and legal concerns regarding embryo cryopreservation, increase assisted reproduction flexibility and be a concrete option to save fertility in women with cancer. Recently, egg survival and pregnancy rates improved, with the birth of more than 500 children. The birth rate per thawed oocyte is around 5-6%. As regards safety, data on birth defects seems to be reassuring so far but must be monitored by an international registry. Comparative studies between slow freezing and vitrification in the same patient population are needed to elucidate pros and cons of each technique.

Human oocyte cryopreservation

The clinical role of oocyte cryopreservation in assisted reproduction, as an adjunct to sperm and embryo cryopreservation, has been comparatively slow to evolve as a consequence of theoretical concerns related to efficacy and safety. Basic biological studies in the 1990's alleviated many of these concerns leading to more widespread adoption of the technology. While a number of babies were born from the approach validated in the 1990's, its perceived clinical inefficiency led to the search for improved methods. Introduction of elevated dehydrating sucrose concentrations during cryopreservation increased survival and fertilization rates, but there is no well-controlled evidence of improved clinical outcome. Similarly, the use of sodium-depleted cryopreservation media has not been demonstrated to increase clinical efficiency. More recently, and in the absence of basic biological studies addressing safety issues, the application of vitrification techniques to human oocytes has resulted in reports of a number of live births. The small number of babies born from clinical oocyte cryopreservation and the paucity of well-controlled studies currently preclude valid comparisons between approaches. Legal restrictions on the ability to select embryos from cryopreserved oocytes in Italy, where many of the available reports originate, also obscure attempts to assess oocyte cryopreservation objectively.