The female system has to deal with some key challenges, from the entrance of the foreign semen, to the implantation of the embryo and the formation of the placenta.
In response to these complex challenges, changes in gene expression, particularly in the female immune system, have been related to a status of relative tolerance, but, at the same time, the occurrence of a selection process during the travel of sperm through the entire female genital.
Sperm membrane receptors, small RNAs (free-, exosome- or sperm-related) and other molecules may play relevant roles in this “female-male understanding process”. However, sperm quality in human has dramatically worsened in the western hemisphere, requiring of assisted reproduction for procreation.
Relevant sperm quality parameters must be carefully studied and diagnosed to determine reasons behind this deterioration. An example is DNA stability, an optional parameter according to WHO-semen diagnostics whose relevance for embryo development is obvious.