Sample Mixing for Semen Analysis – WHO 5th Edition 2.4.1 (Pages 17 and 18)
For Manual and Automated Semen Analysis:
The nature of the liquefied ejaculate makes taking a representative sample of semen for analysis problematical. If the sample is not well mixed, analysis of two separate aliquots may show marked differences in sperm motility, vitality, concentration and morphology. To be certain of obtaining reproducible data, the sample should be thoroughly mixed before aliquots are taken for assessment.
Sample Mixing Instructions:
Before removing an aliquot of semen for assessment, mix the sample well in the original container, but not so vigorously that air bubbles are created. This can be achieved by aspirating the sample 10 times into a wide-bore (approximately 1.5 mm diameter) disposable plastic pipette (sterile when necessary). Do not mix with a vortex mixer at high speed as this will damage spermatozoa.