Looking down on sperm motion: a useful added dimension?

The assumed association of sperm motility with fertility has long been a preoccupation of clinicians. Whereas assessing fertility of a couple has relatively easy end-points (time to pregnancy, number of children), assessing motility does not. The many methods developed to determine it include assessing a sperm population subjectively (by grading) and objectively (by measuring its motion-induced movement into a light beam by spectrophotometry or nephelometry), and making measurements on individual sperm cells (by stroboscopic or multiple-exposure photography or digitized video-recordings). A new technique reported recently1 involves holography to determine unrestrained movement patterns of objects in deep chambers over long periods of time. It has been used to provide information on the temporal motility patterns of unrestrained spermatozoa swimming in three-dimensions (hence four-dimensional motility).