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Background. Patients with poor ovarian response to ovarian hyperstimulation represent an interesting group for studying the impact of embryo cleavage irregularities on clinical outcome since all embryos, regardless of their quality, are usually transferred to the uterus. The aim of our study was to follow the morphokinetics of fertilized oocytes from natural cycles in poor responders. Methods. Zygotes from 53 cycles were cultured in vitro for 3 days. The morphokinetics of their development and transfer outcomes were retrospectively analyzed for the normally and irregularly cleaved embryos. Results. Of all embryos, 30.2% had single and 20.8% multiple cleavage irregularities with the following prevalence: developmental arrest 30.2%, direct cleavage to more than two cells 24.5%, chaotic cleavage 13.2%, and reverse cleavage 11.3%. These embryos had longer pronuclear phases, first cytokinesis, second embryo cell cycles, and less synchronized divisions. The transfer of normally developing embryos resulted in an implantation rate of 30.8% and a delivery rate of 23.1%, but irregularly cleaved embryos did not implant. Conclusions. The use of time-lapse microscopy in poor responder patients identified embryos with cleavage abnormalities that are related with no or extremely low implantation potential. Gained information about embryo quality is important for counselling patients about their expectations. [ABSTRACT FROM AUTHOR]

Numerous studies show the beneficial effect of reduced oxygen on the culture of animal embryos in vitro. However, few similar studies have been carried out in humans, and the conclusions from these were contradictory. Using sibling human oocytes, a prospective study was carded out to analyse the effect of 5 and 20% oxygen on prolonged development of embryos. The outcomes measured were fertilization rate and proportion of morphologically optimal embryos, blastocysts and optimal blastocysts developing on day 5. The results were analysed separately for the group of IVF (n = 988 oocytes) and ICSI (n = 928 oocytes) cycles. It was found that low oxygen did not influence fertilization, but in comparison with 20% oxygen, it resulted in a significantly higher proportion of embryos being optimal on day 3 after IVF (59 versus 43.2%; P < 0.001 ) as well as after ICSI cycles (51.2 versus 28.5%; P < 0.001). In both methods, the lower oxygen concentration improved the blastulation rate (73.2 versus 63. 1%; P < 0.05 and 67.4 versus 54.7%; P < 0.001) and increased the proportion of embryos reaching the stage of expanded blastocyst with normal inner cell mass on day 5 (31.1 versus 14.6%; P < 0.001 and 18.9 versus 11.4%; P < 0.01 ). The ratio of successful embryo development to optimal blastocyst stage on day 5 of culture, calculated for two oxygen concentrations, was 2.1 for IVF and 1.7 for ICSI, in favour of lower oxygen tension. [ABSTRACT FROM AUTHOR]