According to the latest WHO manual of 2010, the lower reference limit for sperm concentration is 15 million spermatozoa per milliliter of ejaculate. When no spermatozoa are found in the ejaculate, the sample should be centrifuged and the pelled (concentrated post-centrifuged product) is examined again. If spermatozoa appear in this centrifugation, we call it cryptozoospermia (< 100000 spermatozoa/mL) and, if no spermatozoa are found, we speak of azoospermia (0 spermatozoa/mL).Normally, when the male is diagnosed with cryptozoospermia, the recommended reproductive treatment is IVF-ICSI. In the case of conventional incubation each oocyte is incubated with 50,000 - 100,000 spermatozoa, so in cases of cryptozoospermia the number of sperm obtained would be insufficient to incubate several oocytes. Thus, in cases of very altered semen samples (as in the case of cryptozoospermia) to fertilize all the oocytes obtained in an IVF cycle we perform fertilization by ICSI.ICSI consists of the microinjection of a single spermatozoon into an oocyte. Thus, only one sperm is needed for each oocyte obtained, and it is the technique of choice in cases of cryptozoospermia.
