In vivo occurs after ejaculation, when sperm come into contact with secretions from the female genital tract. Sperm do not capacitate all at the same time, so when they find the oocyte some of them will have already completed this process. During the capacitating process, the sperm undergoes a series of changes such as:
- Modifications at the level of the head (acrosome) facilitating the capacity to join the pellucid zone of the oocyte to then start the acrosome reaction, i.e. release of acrosome to be able traverse the oocytary layers and fertilize the oocyte
- The movement of the sperm is no longer rectilinear and progress with high amplitude beating pattern motion caused by strong pulses of head towards right and left (hyperactive movement). This movement, more vigorously, facilitates penetration and entrance to the oocyte.
In Vitro, the capacitating process is performed in the laboratory by washing and subsequent sample centrifugation of ejaculate. These results in recovering the hyperactive and morphologically normal progressive motile spermatozoa from the total sample.
The sperm capacitation is also called REM or “Recovery of Mobile Sperm” and it is performed as a biological diagnostic test or also to prepare the sperm sample to make an artificial insemination or fertilization in vitro, in any of its variations.