It is expected that the definition of common terminology and standardization of laboratory practice related to embryo morphology assessment will result in more effective comparisons of treatment outcomes. This document is intended to be referenced as a global consensus to allow standardized reporting of the minimum data set required for the accurate description of embryo development.

No abstract

Although human embryos will develop in vitro for six days or more, little is known about the effects of the primary nutrients, pyruvate and glucose, on development. Because the nutrient requirements of embryos change throughout preimplantation development, the effects of altering substrate concentrations in the culture medium were examined, using 'surplus' human preimplantation embryos cultured from the two-four-cell stage to the blastocyst stage in medium containing various concentrations of pyruvate and glucose. Between the one-cell stage and the two-four-cell stage all of the embryos were exposed to 0.47 mmol pyruvate l-1 and 5.5 mmol glucose l-1. Pyruvate as sole substrate in the medium could support blastocyst development to an extent of 59% (10 of 17). Conversely, culture of embryos in pyruvate-free medium resulted in the developmental arrest of 84% (21 of 25) of embryos, and for the 16% (4 of 25) that did reach the blastocyst stage there was a significant decrease in metabolic activity on day 4-5, during the morula to blastocyst stage transition. Embryos could not use glucose to compensate for the lack of pyruvate in the medium. Pyruvate uptake was related to exogenous concentration and optimal development occurred at the highest concentration tested, 0.47 mmol l-1. Embryo development to the eight-cell stage was slightly enhanced 82% (14 of 17) versus 60% (24 of 40) when no glucose was added to the medium, and the resulting blastocysts had significantly more cells (99.1 +/- 13.5 versus 58.4 +/- 8.2; P < 0.02) than did embryos grown in the presence of 1 mmol glucose l-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The number of cells and metabolic activity of male and female human preimplantation embryos were examined to determine whether male embryos are more advanced than female embryos following in vitro fertilization (IVF). The metabolic activity of embryos fertilized normally was assessed daily by non-invasive measurement of pyruvate and glucose uptake and lactate production between days 2 and 6 after insemination. On day 6, the numbers of nuclei from the trophectoderm and inner cell mass of blastocysts were counted by differential labelling and fluorescence microscopy. Nuclei were then recovered and the sex of the embryos identified using nested primers to amplify the amelogenin gene and pseudogene sequences on the X and Y chromosomes, respectively. Development of male and female embryos were then compared retrospectively. From 69 of 178 (39%) embryos that developed to the blastocyst stage, the sex of 57 was determined; 21 (37%) were male and 36 (63%) female. The number of cells in male embryos was significantly greater on day 2 (P < 0.005), and this difference was maintained up to the blastocyst stage (in both the trophectoderm and the inner cell mass), although differences were not always significant. Pyruvate uptake was significantly higher by male embryos between days 2 and 5 (P < 0.05). Glucose uptake and lactate production were significantly higher in male embryos on days 4-5 (P < 0.05); this difference was not significant on days 5-6. Extrapolation from differences in the number of cells indicates that female embryos are approximately 4.5 h delayed in their development from day 2 onwards compared with male embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

We conclude that pyruvate uptake as the sole criterion for embryo selection cannot predict which embryos will implant after transfer. Assessment of embryos using morphological and developmental criteria, therefore, remains the most consistent, though inefficient, indicator of pregnancy potential.

Computer-automated time-lapse analysis has been shown to improve embryo selection by providing quantitative and objective information to supplement traditional morphology. In this multi-centre study, the relationship between such computer-derived outputs (High, Medium, Low scores), embryo implantation and clinical pregnancy were examined. Data were collected from six clinics, including 205 patients whose embryos were imaged by the Eeva™System. The Eeva scores were blinded and not considered during embryo selection. Embryos with High and Medium scores had significantly higher implantation rates than those with Low scores (37% and 35% versus 15%; P < 0.0001; P = 0.0004). Similar trends in implantation rates were observed in different IVF centres each using their own protocols. Further analysis revealed that patients with at least one High embryo transferred had significantly higher clinical pregnancy rates than those with only Low embryos transferred (51% versus 34%; P = 0.02), although patients’ clinical characteristics across groups were comparable. These data, together with previous research and clinical studies, confirm that computer-automated Eeva scores provide valuable information, which may improve the clinical outcome of IVF procedures and ultimately facilitate the trend of single embryo selection.

Non-invasive microanalytical methods have been devised to study the energy metabolism of single human preimplantation embryos. Pyruvate, which is added routinely to all media used to culture human embryos, is consumed throughout the preimplantation period, with glucose assuming an increasing role at embryo compaction and blastocyst formation. All of the glucose consumed may be accounted for by the appearance of lactate in the incubation medium. The enzyme hexokinase may be involved in regulating this aerobic glycolysis. There is considerable indirect evidence for the utilisation of endogenous as opposed to exogenous energy substrates, the most likely candidate being protein. Information on early human embryo metabolism is likely to find application in a number of areas: these include the improvement of techniques for assisted human conception, notably in the selection of embryos for transfer following In Vitro Fertilisation; the diagnosis of genetic defects at the preimplantation stage; increased understanding of the causes of implantation failure and miscarriage, and the development of novel post-coital contraceptives.

No abstract