Specific sperm defects are differentially correlated with DNA fragmentation in both normozoospermic and teratozoospermic subjects

Abstract

A positive effect of selecting spermatozoa under high magnification during intracytoplasmic sperm injection (ICSI) has been described, but a clear explanation has not been given yet. Previous works have shown that high magnification selected spermatozoa have significantly better chromatin status than unselected cells; on the other hand, it has been reported that spermatozoa with no morphological defects can also be negatively associated with embryo quality and pregnancy outcome attributable to DNA fragmentation. The aim of this study was to investigate whether sperm morphology is correlated with DNA fragmentation, both in normozoospermic and teratozoospermic patients. A prospective cohort study involving 32 subjects was recruited over a 3-month period. Spermatozoa were fixed on a slide for TUNEL assay and evaluated using an epifluorescent light microscope equipped with a video monitor. Single TUNEL-positive or -negative cells were evaluated for morphology at ×4400 magnification. Each spermatozoon was then classified according to morphological normalcy or specific defects. The median percentage of typical forms was 11 and 0%, in the normozoospermic and teratozoospermic groups respectively (p = 0.001). In normozoospermic samples, the percentage of TUNEL-positive morphologically normal spermatozoa was 4%. By comparison, spermatozoa showing a vacuolated head or a small non-oval head had a significantly higher incidence of DNA fragmentation in both groups (12 and 13%, 19 and 13% respectively; p < 0.05). In contrast, spermatozoa showing a pyriform head had a DNA fragmentation rate similar to typical forms (3 and 5%, in normozoospermic and teratozoospermic respectively). This study shows that specific defects evaluated in fixed spermatozoa under high-power magnification are more likely to be associated with DNA fragmentation. High-magnification evaluation of spermatozoa can therefore reduce the probability of selecting cells carrying fragmented DNA during ICSI.

Keywords: TUNEL assay; sperm morphology; sperm quality parameters; spermatozoa.