Is semen analysis useful to predict the odds that the sperm will meet the egg?

Any mammalian spermatozoon that achieves successful in vivo fertilization has to perform almost perfectly in many disparate functions and overcome a series of obstacles imposed by the female reproductive tract. This implies that during formation in the testis and epididymis, the spermatozoa did not incur any morphological, metabolic, immunological or genetic abnormalities. Given that the spermatozoa are such highly differentiated cells, this means that every cellular compartment must not only be intact but must also respond appropriately to intracellular and extracellular signals. Assuming that a spermatozoon possesses this level of perfection, and is able to reach and penetrate an oocyte, it can only be regarded as 'fertile' if the DNA it carries is intact and able to sustain embryonic development. Although the proportion of inseminated spermatozoa that meet these criteria is vanishingly small, the female reproductive tract applies stringent selection criteria during sperm transport and, as a result, the probability of conception around the time of ovulation is very high. If laboratory tests of semen quality could approach the efficacy of the female reproductive tract, it would be possible to predict the odds of spermatozoa meeting the egg; however, this is not possible at present. In this article, I suggest a simple model to illustrate how a battery of laboratory tests could eventually be used to make these predictions.