Liquefaction should be complete before viscosity is assessed.
Semen viscosity can be estimated by aspirating the sample into a wide-bore plastic disposable pipette, allowing the semen to drop by gravity and observing the length of the thread that is formed. A normal sample leaves the pipette in small drops with very little trailing thread. A semen sample that is abnormally viscous will form a thread more than 2 cm long.
A specimen that is more viscous than normal after liquefaction may have reduced sperm motility. During sexual intercourse, hyperviscosity can prevent the sperm from reaching the cervix.