Improving sperm cell analysis: a new WHO manual

The wait is over…The new WHO Semen Analysis manual – version six – is now live! It's been 11 long years since the last one (2010 fifth edition). We have been on the edge of our seats waiting. However, we can now relax, take a deep breath, and digest its contents to our heart's content.

The WHO manuals have been the cornerstone of male reproductive health since 1980. The first manual, published in 1980 had only six pages dedicated to density of semen (concentration), motility and morphology of sperm. Subsequent editions became increasingly more comprehensive providing detailed protocols. The second edition was more comprehensive but it was the the third edition published in 1992, that provided a real change in the definition of sperm morphology. WHO set an 'empirical reference value of 30 percent normal forms and above as normal', which meant that 30 percent of the sperm in a semen sample needed to have normal morphology for the patient to be considered fertile. This replaced the previous 50 percent limit. One of us (Professor Christopher Barratt) wrote several critical commentaries on this 'change', including a commentary in Human Reproduction.

Issues with lack of evidence to back up parameters considered fertile or normal for semen analysis continued in the next, fourth, edition. However, the fourth edition saw the emergence of detailed quality control procedures, which were an attempt to address the poor way semen analysis was performed worldwide – more on this later.

For the first time, the fifth edition published in 2010 provided 'reference ranges' for sperm concentration backed up by significant clinical data. The reference ranges were a major discussion point as the 'normal' concentration was reduced from 20 million per ml to 15 million per ml. This stimulated a plethora of feedback and came at a time when there was considerable concern about a decline in global sperm counts (some say this remains with us, but that's a discussion for another day). This reduction in what could be considered normal sperm concentration was simply because, for the first time, we had a large body of data to describe the other semen characteristics of fertile men.

Now the history lesson is over, what is in the eagerly awaited and newest manual, the sixth edition. To summarise: the WHO returned to the four-category classification of sperm motility: rapid progressive, slow progressive, non-progressive and immotile, and no replicate assessments are now needed in vitality and morphology assessments. Other changes include the introduction of sperm DNA fragmentation tests (yes – in for the first time), markers for genital tract inflammation, anti-sperm antibodies and sperm aneuploidy assessments. Interestingly, under the categorisation of research procedures some are included for the first time such as, CatSper for ion channel detection and sperm chromatin assay, which looks at the packaging of DNA in the cell. However, the sixth edition has discarded two tests: sperm cervical penetration and hamster egg penetration, as they lacked sufficient evidence for inclusion.

There is lots to discuss but we believe two key aspects of the sixth edition warrant more detailed comment:

1. The aim of the sixth edition is to provide an international set of protocols and guidance to make semen analysis more accessible, understandable and comparable between centres. Coincidentally the sixth edition will be supported by new International Organisation for Standardisation (ISO) standards for semen analysis (ISO 15189:2012, ISO 23162:2021) which may also help in the long-standing goal of achieving global standards for semen analysis. There is an urgent need to improve standards. The aim of the manual is to provide evidence-based standardisation of protocols to produce robust and comparable data. Standardisation is a continual challenge for in andrology. Since the 1940s there have been reports about the lack of standardisation of semen analysis and poor adherence to protocols (Harvey and Jackson, 1945). A plethora of data, as shown by Zuvela and Matson in Reproductive Biomedicine, show that, even now, only a minority of laboratories follow the WHO procedures outlined in these manuals, even those enrolled on an professional external quality assurance schemes.

2. Providing more comprehensive data on fertile males. The original reference range data from 2010 have been significantly added to. The new edition is based on analysis published this year in the journal Andrology that incorporates over 3500 subjects from twelve countries and five continents. This constitutes the most comprehensive data on a fertile male population ever produced. Moreover, to aid in transparency and continual assessment, the data is freely available and can be examined, added to and reanalysed as and when appropriate.

The sixth edition is a significant improvement on its predecessors. However, the real gamechanger, is for us as reproductive biologists to follow the manual and produce reliable robust data from semen analysis. Although we have universally failed to do this so far, we are optimistic, with these new tools and these new guidelines, we are now able to provide high quality analysis for our patients.