Spermatozoa of subfertile men contain significantly higher thiol concentrations as compared with those of fertile men. The detrimental effect on embryo quality of a high Hcy concentration in the ejaculate and in follicular fluid is intriguing and may suggest that Hcy is inversely associated with fertility outcome.

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Systems to assess the toxicity of materials used in human assisted reproduction currently lack efficiency and/or sufficient discriminatory power. The development of 1-cell CBA/B6 F1 hybrid mouse embryos to blastocysts, expressed as blastocyst rate (BR), is used to measure toxicity. The embryos were divided into control and test groups, and were exposed to either control medium or to a potentially toxic test medium. Inferences on toxicity were based on differences in BR between the two groups. The mouse embryo assay followed a stratified (mouse), randomized (embryo), and balanced (equal number of embryos per group and per mouse) design. The number of embryos needed was calculated using power analysis. The basal BR of the hybrid strain was determined in a historical population. Sixty-nine mouse embryos per group were required to detect toxic materials with sufficient sensitivity and to account for the considerable inter-mouse variation in blastocyst development. Fifty-two samples, divided over batches of seven different products were tested before use in the study IVF centre and five of these were found to be toxic. This test system, presented as the Nijmegen mouse embryo assay (NMEA), can be used to detect embryo-toxic materials in daily IVF practice, and this report may provide a starting point for standardization.

To study the effects of sperm density on the results of computer-assisted semen analysis (CASA), 10 washed semen samples were diluted and measured with the CellTrak/S CASA system in a concentration range of 10-180 x 10(6) spermatozoa/ml. All sperm motility parameters were influenced to some extent by sperm density. The motility percentage was influenced significantly in 5 samples (P < 0.005), the straight line velocity in all samples (P < 0.0005 in 7 samples), the curvilinear velocity in 3 samples (P < 0.005), the linearity in 9 samples (P < 0.0005 in 6 samples) and the lateral head displacement in 9 samples (P < 0.005 in 6 samples). In general, the CellTrak/S data are influenced significantly if sperm density exceeds 50 x 10(6) spermatozoa/ml. The influence of sperm density on the motility parameters can be explained both by the accuracy of the CASA system and by actual changes in the motility of the spermatozoa. In the light of other published studies, it is concluded that sperm motility measurements with CASA systems should be assessed using 25-50 x 10(6) spermatozoa/ml, especially in studies concerning lateral head displacement and the linearity, as in sperm hyperactivation studies.