Methods of sperm preparation for assisted reproduction

Because seminal plasma contains factors which inhibit the fertilising ability of spermatozoa, it is essential that spermatozoa be separated from it quickly and efficiently. Four basic approaches for this exist: (1) simple dilution and washing; (2) sperm migration (either direct from liquefied semen, from a suspension of washed spermatozoa or from a washed sperm pellet); (3) selective washing procedures (mainly Percoll and Nycodenz density gradients); and (4) adherence methods for the elimination of debris and dead spermatozoa (glass wool, glass beads and Sephadex columns). While the success of a sperm preparation method is often assessed by its yield of motile spermatozoa, it is also vital that sperm preparations for clinical use should be free of any microbiological contaminants present in semen. Other relevant considerations in choosing a method include its technical complexity as well as its material, apparatus and time costs. Any possible exposure of spermatozoa during preparation to deleterious influences that may cause iatrogenic sperm dysfunction must obviously be avoided at all costs. Consequently, methods involving centrifugal washing steps prior to the selection of motile spermatozoa should be discontinued. Direct swim-up from semen remains the simplest way to obtain populations of highly motile spermatozoa and, dependent upon the absolute yield required, can be a very rapid procedure with normal semen samples. Abnormal samples, especially those with increased viscosity, may benefit from a prior filtration on a glass bead or Sephadex column. The initial motile sperm preparation should be washed once (perhaps twice) to minimise seminal plasma contamination of the final preparation. Several rapid, simple discontinuous Percoll gradients giving excellent yields are available.(ABSTRACT TRUNCATED AT 250 WORDS)