Trail wash is necessary to assess the basic sperm parameters (i.e. count; motility & morphology) after removing the seminal fluid and dead sperms.
Sometimes the raw sperm’s parameters and post wash sperm’s parameters differ and it help us to categorise that sample for future treatment (IUI/IVF/ICSI).
It can be done with the help of Density Gradient Technique or Sperm Swim up Technique.