Influence of deoxyribonucleic acid damage on fertilization and pregnancy.

To investigate sperm DNA damage in relation to fertilization and pregnancy. Prospective study. The Institute of Reproductive Medicine, Giessen, Germany. Semen collected from 249 patients attending the IVF program. The percentage of terminal deoxynucleotidyl transferase-mediated dUDP nick-end labeling- (TUNEL-), Fas-, and annexin-V-positive sperm and the proportion of green-fluorescing sperm in the acridine orange stain was determined and correlated with sperm concentration, motility, fertilization, and pregnancy. Significant correlations with the concentration of motile sperm were only found for the acridine orange stain (before and after sperm separation) and for the TUNEL assay (after sperm separation). Moreover, patients whose sperm had a high percentage of DNA fragmentations showed significantly lower pregnancy rates (TUNEL assay: 19.05% vs. 34.65%; acridine orange stain: 24.58% vs. 37.93%). The apoptosis parameters (annexin V binding and Fas expression) showed no statistically significant differences. Our data clearly demonstrate that DNA fragmentation, as determined by the TUNEL assay, is predictive for pregnancy in IVF. This implies that spermatozoa with DNA fragmentation can still fertilize an oocyte but that when paternal genes are "switched on," further embryonic development stops, resulting in failed pregnancy. It seems that, at least in the patients we analyzed, apoptosis in the sperm does not play a role for fertilization. This would imply that DNA fragmentation in human spermatozoa is caused by external factors, such as reactive oxygen species, rather than by apoptosis.