How to select immotile but viable spermatozoa on the day of intracytoplasmic sperm injection? An embryologist's view.

A viable spermatozoon is the prerequisite for initiating fertilization in intracytoplasmic sperm injection. Usually motility is the primary sign used to determine a sperm's viability. However, in every in vitro fertilization (IVF) laboratory cases are observed in which none or only few spermatozoa are motile. This can occur in treatment cycles involving ejaculated samples but is most common in cases where surgically extracted testicular spermatozoa are used. To aid in selection, several techniques have been developed to identify viable spermatozoa from the immotile fraction. Amongst the more commonly used approaches are (i) the hypo-osmotic swelling test (ii) chemical substances for induction of tail movements (iii) the sperm tail flexibility test and (iv) laser-assisted immotile sperm selection. All can be used routinely in an IVF laboratory with each having both strengths and weaknesses. It is the purpose of this short review to focus on the technical issues involved in the performance of each of these techniques and to highlight the advantages and disadvantages of each approach.