Clinical experiences of ICSI-ET thawing cycles with embryos cryopreserved at different developmental stages

The impact of laser-assisted hatching on the outcome of frozen human embryo transfer cycles

Biochemical modifications of zona pellucida (ZP) result in zona hardening. Zona hardening (ZH) is induced by several factors such as advancing maternal age, in vitro culture conditions and cryopreservation and adversely effects implantation. The objective of the clinical study was to determine whether or not laser-assisted hatching (LAH) applied on day 3 frozen embryos improves the outcome of frozen embryo transfer (FET) cycles in patients with recurrent implantation failure and/or advanced female age. In total, 413 patients of different ages with recurrent implantation failure (maximum three cycles) were involved into the study. Patients were allocated randomly into LAH and control groups. On the day of FET, after thawing and just before FET, the ZP was thinned using a laser system. In the control group no treatment was applied on frozen embryo before transfer. The main outcome measures were clinical pregnancy rate. Overall, the results indicate a tendency that LAH increased (P = 0.08) clinical pregnancy. However, for patients older than 37 years, LAH increased pregnancy rates significantly (P = 0.03). In the LAH and control groups, the age of patients and the number of transferred embryos influenced pregnancy rates (P = 0.01). For patients older than 37 years, no effect of number of transferred embryos was detected (P = 0.14). The incidence of multiple pregnancies also increased in the LAH group (P = 0.01). In conclusion, in older woman, to overcome the negative effect of zona hardening, LAH could be performed on frozen embryos as a routine strategy before FET in frozen cycles in order to increase the possibility of pregnancy formation.

Different chromatin and energy/redox responses of mouse morulae and blastocysts to slow freezing and vitrification

BACKGROUND

The ability to cryopreserve mammalian embryos has become an integral part of assisted reproduction, both in human and veterinary medicine. Despite differences in the size and physiological characteristics of embryos from various species, the embryos have been frozen by either of two procedures: slow freezing or vitrification. The aim of our study was to compare the effect of slow freezing and vitrification to the chromatin structure, energy status and reactive oxygen species production of mouse morulae and blastocysts.

METHODS

Mouse morulae and blastocysts were randomly allocated into vitrification, slow freezing and control groups. For slow freezing, Dulbecco phosphate buffered saline based 10% glicerol solution was used. For vitrification, G-MOPS™ based solution supplemented with 16% ethylene glycol, 16% propylene glycol, Ficoll (10 mg/ml) and sucrose (0.65 mol/l) was used. After warming, the chromatin integrity, mitochondrial distribution pattern and energy/oxidative status were compared among groups.

RESULTS

Cryopreservation affected chromatin integrity at a greater extent at the morula than the blastocyst stage. Chromatin damage induced by slow freezing was more relevant compared to vitrification. Slow freezing and vitrification similarly affected mitochondrial distribution pattern. Greater damage was observed at the morula stage and it was associated with embryo grade. Cryopreservation altered the quantitative bioenergy/redox parameters at a greater extent in the morulae than in the blastocysts. Effects induced by slow freezing were not related to embryo grade or mitochondrial pattern, as affected embryos were of all grades and with both mitochondrial patterns. However, effects induced by vitrification were related to mitochondrial pattern, as only embryos with homogeneous mitochondrial pattern in small aggregates had reduced energy status.

CONCLUSIONS

This study shows for the first time the joint assessment of chromatin damage and mitochondrial energy/redox potential in fresh and frozen mouse embryos at the morula and blastocyst stage, allowing the comparison of the effects of the two most commonly used cryopreservation procedures.

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.