Slow programmable and ultra-rapid freezing of human embryos

Appendix F: Quinn's Advantage Embryo Freeze Kit

Despite a large focus on the use of vitrification to cryopreserve embryos in recent years, there are still arguments for the use of slow freezing for the cleavage-stage embryo. Having said this, there are lessons to be learned from the process of vitrification that could be applied to slow freezing to improve post-thaw survival and ultimately clinical pregnancy rates. Specifically, increasing the concentration of sucrose in the freezing solution from 0.1 to 0.2 M and subsequently increasing the sucrose concentrations in thawing solutions could prove beneficial. The use of vitrification warming solutions in the thawing of slow-frozen embryos may also be an option that not only improves survival but also streamlines product purchasing and protocols within the laboratory.

[Vitrification: Principles and results]

Sperm and embryos cryopreservation is a commonly applied technique for several years. Recently authorized in France, vitrification tends to replace gradually the conventional technique of slow freezing, so upsetting the practices in the management of patients. It allows from now on the cryopreservation of oocytes and opens new perspectives in egg donation either still in fertility preservation. This review thus attempted to examine the contribution of vitrification in the freezing of oocytes and human embryos at various stages of development. If obviously vitrification appears as the current method of choice for the cryopreservation of oocytes as well as blastocysts, the results are less cut as regards embryos to early stages. No increase in adverse obstetric and perinatal outcomes in children conceived from vitrified oocytes or embryos is noted in the literature.

A critical appraisal of cryopreservation (slow cooling versus vitrification) of human oocytes and embryos

BACKGROUND

Vitrification is now a commonly applied technique for cryopreservation in assisted reproductive technology (ART) replacing, in many cases, conventional slow cooling methodology. This review examines evidence relevant to comparison of the two approaches applied to human oocytes and embryos at different developmental stages.

METHODS

Critical review of the published literature using PubMed with particular emphasis on studies which include data on survival and implantation rates, data from fresh control groups and evaluation of the two approaches in a single setting.

RESULTS

Slow cooling is associated with lower survival rates and compromised development relative to vitrification when applied to metaphase II (MII) oocytes, although the vitrification results have predominantly been obtained using direct contact with liquid nitrogen and there is some evidence that optimal protocols for slow cooling of MII oocytes are yet to be established. There are no prospective randomized controlled trials (RCTs) which support the use of either technique with pronuclear oocytes although vitrification has become the method of choice. Optimal slow cooling, using modifications of traditional methodology, and vitrification can result in high survival rates of early embryos, which implant at the same rate as equivalent fresh counterparts. Many studies report high survival and implantation rates following vitrification of blastocysts. Although slow cooling of blastocysts has been reported to be inferior in some studies, others comparing the two approaches in the same clinical setting have demonstrated comparable results. The variation in the extent of embryo selection applied in studies can lead to apparent differences in clinical efficiency, which may not be significant if expressed on a 'per oocyte used' basis.

CONCLUSIONS

Available evidence suggests that vitrification is the current method of choice when cryopreserving MII oocytes. Early cleavage stage embryos can be cryopreserved with equal success using slow cooling and vitrification. Successful blastocyst cryopreservation may be more consistently achieved with vitrification but optimal slow cooling can produce similar results. There are key limitations associated with the available evidence base, including a paucity of RCTs, limited reporting of live birth outcomes and limited reporting of detail which would allow assessment of the impact of differences in female age. While vitrification has a clear role in ART, we support continued research to establish optimal slow cooling methods which may assist in alleviating concerns over safety issues, such as storage, transport and the use of very high cryoprotectant concentrations.

Assisted reproductive technologies in Thailand: 2001-2007 results generated from the ART Registry, Royal Thai College of Obstetricians and Gynaecologists

AIM

To present the results of assisted reproductive technology (ART) performed in Thailand during 2001-2007.

METHODS

All licensed ART centers are obliged to submit annual reports on the number of patients, cycles, ART techniques and treatment outcomes to the Reproductive Medicine Subcommittee of the Royal Thai College of Obstetricians and Gynaecologists. Data from all centers were aggregated and analyzed retrospectively.

RESULTS

Cycles were categorized into fresh and frozen/thawed embryo transfer (FET) cycles. Initiated cycles in the first category for 2001 to 2007 were 2183, 2112, 2780, 2717, 3458, 3579 and 4288, respectively. FET cycles during the same period were 467, 558, 733, 768, 1136, 1210 and 1473, respectively. The average pregnancy rate for in vitro fertilization (IVF) was 28.9% per retrieval (range, 26-32.3%) or 33.8% per transfer (range, 30.7-38.6%). Multiple pregnancies (of which 89.3% were twins) from all treatment procedures during this period were 11.4% (range, 9.2-14.5%). A congenital abnormality was reported in 0.56% of live births. The number of embryos per transfer in IVF decreased from 4.1 to 2.9, with no drop in pregnancy rates. Oocyte insemination by intracytoplasmic sperm injection (ICSI) was utilized more often than standard IVF, while gamete intrafallopian transfer and zygote intrafallopian transfer were almost completely replaced by IVF/ICSI. There was a significant difference in pregnancy rates (P < 0.01) when clinics were classified by cycle volumes (<100, 100-400 and >400 cycles/year).

CONCLUSIONS

Despite many limitations, the data provided in this report will help patients, clinicians and policy makers understand the current situation of ART practice in Thailand.

Bibliography. Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 February 2008 and 31 January 2009 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.