Heads and tails: requirements for informative and robust computational measures of sperm motility

The ability of sperm to self-propel through the female reproductive tract is essential for natural fertilisation. Despite this fact, manual assessments of motility are limited in scope and computer-aided sperm analysis (CASA) systems are not routinely used in clinical practice. One significant factor hindering the clinical use of CASA systems is the lack of evidence linking motility measures and fertility outcomes. To progress these technologies, we need to address the variations in the way samples are prepared and imaged, and whether current kinematic parameters provide the physiological insight necessary for establishing these links. In this manuscript, we discuss how preparation (sample viscosity, temperature, concentration), acquisition (chamber depth, frame rate, duration) and analysis can dramatically affect CASA results. With the aim of advancing the clinical application of CASA, we outline the requirements for obtaining measurements that can be compared between samples and systems. We further highlight how the introduction of flagellar tracking can form the basis of increasingly insightful diagnostics; by combining kinematic data with mathematical modelling experimentally intractable details can be uncovered, such as metabolic requirements of motility from a single cell to the population level.