Definition of Normal Sperm Morphology
Morphology simply refers to the shape of the sperm. When a sperm sample is produced, part of the sample is prepared to allow easy visualisation of sperm structure so that the proportion of normal sperm, and those falling into tightly defined morphological groups may be counted. It is exactly the same process whether the sample is produced for a semen analysis or if it is to be used as part of an IVF or IUI cycle.
The World Health Organisation (WHO) lay down strict morphological criteria defining the various sperm defects and these are usually simplified for reporting as the percentage of sperm exhibiting head, midpiece or tail defects. The effect of this is that quite often only a very small proportion of sperm are categorised as normal. In fact a semen sample is considered morphologically normal if 4% of the sperm fulfil the normal criteria. Put another way, a sample may exhibit 96% abnormal morphology and still be within the normal range.
Normal Percentage of Sperm With Normal Morphology
The WHO morphology definitions are very specific so that semen quality can be recorded extremely accurately. Having abnormally shaped sperm is known as teratozoospermia. It’s quite likely that some of the sperm that are categorised as abnormal may actually function normally, but even if this were not so, an average semen sample containing say 100 million sperm in total, where 96% of them were classed as morphologically abnormal, would still have 4 million normal sperms available!
As with other factors, the incidence of poor morphology has increased over the years and in recent years the WHO have redefined normal numbers as 4% of the total rather than the previous 6%.
At Concept Fertility we score morphology using Kruger’s Strict Criteria, the classification recommended by the WHO. Cases where the cut-off value of 4% of normal forms is not achieved are diagnosed as terarozoospermia. Morphology should be used along with other parameters, and not on its own when determining clinical implication.