Natural sperm birefringence can be used to estimate sperm viability and morphology.

Semen parameters were evaluated by a variety of tests. A polarizing microscope (PM) which allows, in a single step, for the evaluation of the number, motility, viability of sperm using the phenomenon of birefringence was used. This approach avoids a Papanicolaou staining procedure modified for sperm (PAP) performed in fixed material. The aim of this study was to examine the birefringence of sperm structures, in live cells, for the direct analysis of morphology on fresh samples. Semen samples from 15 men of recently proven fertility and from 66 male patients who attended our center for semen analysis were examined by polarization microscope (PM) analysis in order to find an index representing a pool of sperm with normal morphology and progressive motility. The receiver operating characteristics (ROC) curves were used to determine the performance of the proposed diagnostic method. The difference between the two areas under the ROC curves (PAP=0.76 and PM=0.82) was quantitatively not significant (P=0.308); however, the curve of the PM method was always higher than the curve of PAP, revealing that, qualitatively, PM was more sensitive than PAP. The PM index can represent the percentage of motile sperm with normal morphology, which is the actual pool of sperm that can reach and fertilize the oocyte. We suggest a PM diagnostic cut-off value of 20%, since this value was the lowest found for individuals of proven fertility.