Objective: To evaluate results of cryoembryotransfers in cycles with estrogen-progestin preparation of the endometrium. Design: Prospective study. Setting: Centre of Assisted Reproduction, Dept. of Obstetrics and Gynecology, Palacký University Medical School, Olomouc. Methods: The study included 51 patients in whom in the period of January to August 2003 altogether 42 cycles the embryotransfer with frozen and thawed embryos were performed. The embryos for cryopreservation were obtained in the classical IVF (n = 21) or ICSI (n = 30) cycles and were cryopreserved in the pronuclear stage (PN). The storage interval varied from 3 months to 5 years. The endometrial preparation was performed in all cycles with oral estrogen – progestin substitution. Embryos in the PN stage were examined for survival (rate of intact embryos after thawing) and progress of their further development. Endometrial thickness, number of transferred embryos, pregnancy rate (PR), implantation rate (IR) and abortions (AB) were evaluated as outcome parameters. Results: A total of 210 thawed embryos were evaluated. Survival was 79% without regard to the method of fertilization. For 42 cryoembryotransfers 131 embryos (62%) in 6 to 10 blastomers after 48 hours cultivation in G 1.2 and G 2.2 fy Vitrolife were selected. Further development was more regular in embryos obtained in classical IVF cycles, where 41% of the embryos were in 4 cells stage after 24 hours of cultivation and 36% of the embryos were in 8 cells stage after 48 hours while after ICSI 32% 4 cells embryos and 26% 8 cells embryos respectively. Endometrial thickness in the day of transfer in all patients was 10.9 ± 1.3 mm, the average number of transferred embryos was 2.4 embryos/transfer, PR was 28.5 (IVF 42.9% and ICSI 20.7%), IR 12.0% (IVF 13.0% and ICSI 11.3%) and AB 41.6% (IVF 33.3% and ICSI 50.0%). Conclusion: Improvement of cryopreservation procedures, freezing of embryos in the pronuclear stage and last but not least the optimal endometrial preparation can positively infl uence the cumulative effi ciency of assisted reproduction.

        Key words: cryopreservation of PN stage, cryoembryotransfer, endometrial hormonal preparation