Sperm testing is not just as simple as putting the sample into a machine and reading out the results. What is normal and how should you interpret the results?

Semen analysis is done by an andrologist who prepares the sample and manually counts and assesses the sperm down the microscope.  This is crucial to bear in mind when it comes to interpreting the results later. But first, what is normal?

Normal or Typical?

Experts keep moving the goal posts when it comes to defining what is normal. The World Health Organisation, produce a manual for how to correctly analyse sperm, and define the ‘normal’ or ‘reference’ values for semen parameters. Until 2010, the normal cut-off criteria were purely arbitrary values chosen by a panel of experts. Present cut-offs come from a study of 4500 men whose partners conceived within a year of trying for a pregnancy. The WHO decided to define normal as results consistent with the best 95% of the men in the study.

Given the methods of defining the reference range, ‘normal’ is probably not the best way of describing sperm test results, because 5% of men’s partners outside the cut off still conceived a pregnancy within a year. A better way of looking at results is seeing if they are typical of with those of a highly fertile male.

The WHO have reference ranges for many different parameters, but in practice we are mainly interested in three—count, motility and morphology.


A sperm count of over 15 million per ml of ejaculate is typical of that of a highly fertile man.


Not all sperm are alive and swimming. In fact, only 32% need to be swimming forward for the sample to be considered typical.


Most sperm are abnormal, dead or in some stage of decay. For example, a big head, two tails, or even two sperm joined together. The WHO says only a measly 4% or more need to have a normal appearance for a typical sample. So if you get a tick in every box, then you can consider that sample to be typical of that of a highly fertile man. But what if it’s not?


One semen analyses is a snapshot of what was present on that specific day. Sperm are being made all of the time, and a short period of illness is enough to affect sperm quality. Furthermore, if sperm have been sat around for a while because of a longer abstinence period, they are more likely to look deformed. Similarly, if a man has recently ejaculated then they may have a lower semen volume and count.  

Lab variation

Remember, semen analysis depends on a real person looking down a microscope. Huge variations exist between labs, even with rigorous quality control.

Abnormal morphology

Often patients, are worried about low morphology, but this is the most controversial of the three parameters and the hardest to measure. Morphology is assessed by the andrologist who will look at 200 sperm and see how many appear normal. Obviously, this may not be representative of the millions within the whole sample, and a difference in one or two sperm can change the overall morphology percentage.

Repeat testing

One atypical sperm test result only provides so much information. The first thing to do is to repeat the analysis after an interval of at least six weeks to look at sperm from another part of the production cycle.

What semen analysis doesn’t explain

Traditional semen analysis is helpful when assessing fertility, but it tells us little about the sperm function. Out of the millions of sperm in one ejaculate, only around a 100 will make it to the egg. Additional sperm tests are on the market to assess DNA fragmentation, cervical mucous penetration, and reactive oxygen species to name a few. Nevertheless, none of these tests have been demonstrated to provide additional information to help direct treatment.


Matt is an NHS Consultant in Newcastle with over ten years of experience. His PhD research into subfertility and miscarriage involved developing a clinical trial and patient engagement.