Sperm washing and preparation

The male partner is asked to produce a semen sample by masturbation or frozen thawed semen is used. In certain case such as retrograde ejaculation, sperm are collected from urine by centrifugation. Only washed and prepared sperm are used for intrauterine insemination because neat semen may cause severe uterine contractions, pains, cramps and sometimes collapse. The aim of washing and preparation of the sperm are to separate sperm from seminal plasma, remove bacteria and other debris and chemicals that may cause infection and irritation and improve sperm capacitation (this increase sperm ability to penetrate and fertilize an egg).

Sperm can be extracted from seminal plasma by a number of different methods.

• Swim up technique separates the good motile sperm by allowing them to 'swim up' into a layer of sterile culture medium. The procedure involves layering sterile culture medium over liquefied semen. Sperm swim up into the culture medium. The upper part of the layered culture medium is removed, and centrifuged and the pellet is re-suspended in a clean sterile medium (sperm wash).
• Density gradient technique separates normal live sperm from seminal plasma and other cells and debris. The procedure involves pipetting semen sample on top of a density gradients column (a layer of fluid containing particles that acts as a filter) and then centrifuged. The normal sperm become concentrated at the bottom of the layer and can then be removed and 'washed' by centrifugation and re-suspension in clean medium.
• Wash in combination with centrifugation. The procedure involves diluting semen sample with a sterile culture medium and centrifuge. Following which the pellet is re-suspended in culture medium and incubated.
  

There is no evidence that one technique is superior to the other, although the trend suggests the density gradient is best (Boomsma et al 2006. Cochrane database).

The presence of one million motile sperm after preparation seems to provide a realistic cut off, below which pregnancy rates plummet. Morphology of sperm is also important and if the proportion of normal sperm falls below 4%, pregnancy is rarely achieved.

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