Evaluation of human spermatozoa in cervical mucus: comparison of different microscopic and extraction techniques

Abstract

This study was designed to describe an accurate and consistent microscopic technique for the assessment of sperm number and motility in sperm-cervical mucus samples, such as those of postcoital tests (PCTs), and to identify a suitable method to extract functional spermatozoa from cervical mucus (CM). Sperm-CM preparations containing various sperm concentrations were counted using three different microscopic illuminations. The dark field-Makler technique was compared with the more classical bright field-slide technique currently used by our clinicians. Several sperm extraction techniques were applied first to bovine (BCM) and then to human (HCM) cervical mucus. Dark field microscopic illumination provided accurate, fast, and easy sperm identification. Counting variability was significantly greater with bright field-slide than with dard field-Makler, while sperm motility was always higher with this latter methodology. A high degree of agreement (intraclass correlation coefficient = 0.965) among three raters, i.e., low interobserver variability, was obtained only with dark field-Makler. Extraction procedures based on "swim-out," Percoll, trypsin, an enzyme cocktail, and mercaptoethanol resulted in small sperm yields in BCM. Mercaptoethanol and trypsin also showed poor sperm recovery in HCM. Among the protocols with the largest yields, the mechanical technique had the largest amount of residual CM, and bromelain reduced sperm motility. The extraction with dithiothreitol (DTT) showed the best results with a mean sperm recovery of 76% and enhanced sperm motility. Sperm viability as well as spontaneous and induced acrosome reaction were conserved in all techniques. In conclusion, use of the dark field-Makler counting technique in combination with DTT extraction of spermatozoa from CM samples, such as those of PCTs, would allow accurate and functional assessment of spermatozoa for preliminary contraceptive efficacy or infertility evaluation.