The influence of in vitro caffeine treatment on human sperm morphology and fertilizing capacity.

After publication in the literature that in vitro caffeine treatment causes damage of the normal shape of the sperm head and thereby decreases fertilizing capacity, we carried out a clinical and electron microscopic study to determine the influence of caffeine on the fertilizing capacity and sperm cell morphology. Sixty women (with infertile husbands) underwent artificial insemination by donor with frozen/thawed semen over a period of 12 months, using randomized addition of caffeine in alternate months. Fourteen women became pregnant during the 6 months they received caffeine-treated semen, whereas only 7 pregnancies occurred during the 6 months the women received semen without caffeine. Scanning electron microscopic examinations of fresh proven donor semen showed no morphologic changes caused by the in vitro caffeine treatment. However, quantitative morphologic analysis of the frozen/thawed semen was unsatisfactory because of the freezing technique and the masking effect of the protective medium. It is concluded that in vitro caffeine treatment of fertile donor semen does not damage the spermatozoa; furthermore, it seems to improve the fertilizing capacity.