The embryo quality of vitrified oocytes was not impaired: cc2, quality according to our hierarchic morphokinetic model, and implantation rates were similar between fresh and vitrified oocytes. However, morphokinetic differences were observed from t2 to tB. Our main study limitation was the retrospective nature of the analysis, although a large database was studied.

A detailed analysis of OC by time-lapse observations enhances the value that these measurements represented as markers of embryo quality, especially during the cytokinesis events produced during preimplantation development.

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Despite efforts made to improve the in vitro embryo culture conditions used during assisted reproduction procedures, human embryos must adapt to different in vitro oxygen concentrations and the new metabolic milieu provided by the diverse culture media used for such protocols. It has been shown that the embryo culture environment can affect not only cellular metabolism, but also gene expression in different species of mammalian embryos. Therefore we wanted to compare the metabolic footprint left by human cleavage-stage embryos under two types of oxygen atmospheric culture conditions (6% and 20% O2). The spent culture media from 39 transferred and implanted embryos from a total of 22 patients undergoing egg donation treatment was analyzed; 23 embryos came from 13 patients in the 6% oxygen concentration group, and 16 embryos from 9 patients were used in the 20% oxygen concentration group. The multivariate statistics we used in our analysis showed that human cleavage-stage embryos grown under both types of oxygen concentration left a similar metabolic fingerprint. We failed to observe any change in the net depletion or release of relevant analytes, such as glucose and especially fatty acids, by human cleavage-stage embryos under either type of culture condition. Therefore it seems that low oxygen tension during embryo culture does not alter the global metabolism of human cleavage-stage embryos.

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