Optimizing the sperm penetration assay with human follicular fluid.

Major limitations of the conventional sperm penetration assay are the inability to assess several aspects of sperm function (zona binding and penetration) and the absence of human ovulatory products known to influence fertilization. We therefore modified the sperm penetration assay by the addition of human follicular fluid (FF) to induce the acrosome reaction in an attempt to improve the false-negative rate of the conventional technique. In 26 patients with negative results, results became positive in 20 with human FF and the acrosome reaction increased fourfold. In 19 different men, we compared the results of the conventional and modified assays with outcome of in vitro fertilization. The false-positive rate was the same, but the false-negative rate was reduced from 40% to 7% with the addition of human FF.