It has been reported that high quality embryos can be selected using the Graduated Embryo Score (GES) on day2 or day3. However it is still unknown whether GES is useful for the selection of day5–6 blastocyst stage embryos. Blastocyst stage embryos were evaluated with the conventional Gardner's classified system on day5 following evaluation with the modified GES system on day2–3, and were then transferred. The pregnancy rate (47.4%) was significantly higher for transferred blastocysts with high GES points (GES ≥ 70) than the pregnancy rate (16.7%) of transferred blastocysts with low GES points (GES < 70) which had been evaluated as high potential quality blastocysts by Gardner's classification. These results suggest that the GES system is useful for the selection of high potential blastocysts in blastocyst transfer cycles. Moreover, the GES may help to promote elective single blastocyst transfer.

Using zona-free mouse eggs treated with mannosidase, the role of mannose on the surface of eggs in fertilization was examined. The fertilization rates of eggs treated with mannosidase at concentrations of 0.05, 0.1, 0.5 or 1.0 units/100 µl were 47.8, 40.4, 28.2 and 18.8%, respectively, which were all significantly lower than the 69.2% of control eggs with no mannosidase treatment. The binding of Canavalia ensiformis agglutinin (Con A), a lectin with an affinity to mannose, was strong on the surface of all control eggs not treated with mannosidase. However, the rate of eggs showing strong Con A-binding was significantly decreased among those treated with mannosidase at a concentration of 0.1 units/100 µl (44.0%). These findings suggest that mannose on the surface of the cytoplasmic membrane, in addition to zona pellucida, of eggs has a possible role in sperm recognition.