A study has suggested sperm testing in UK labs fails to meet World Health Organization standards, raising concerns over misdiagnoses of infertility.
The paper, published online by Human Reproduction, surveyed 37 labs.
Teams from the Universities of Bristol and Sheffield found only five per cent of the clinics met all WHO standards for assessing the size and shape of sperm.
This means clinics could be over-diagnosing certain problems resulting in unnecessary treatments.
Sperm morphology - its size and shape - is known to be a significant indicator of male fertility levels.
It is one of the areas that laboratories analyse to assess whether a man has fertility problems and so doctors can decide if couples need treatment to help them conceive.
Couples affected in this way are offered ICSI (Intracytoplasmic Sperm Injection), where a single sperm is injected directly into a woman's egg.
Over the past 15 years, the WHO has issued a series of recommendations on how clinics should measure sperm morphology.
Nineteen laboratories specialising in sperm analysis and 18 in district general hospitals responded to the survey carried out by researchers from Bristol and Sheffield.
Of the labs surveyed, 43 per cent looked at samples, which were unstained.
Staining fixes sperm in place so they can be analysed more easily, and the WHO recommendations for sperm width and length are based on stained sperm.
The researchers said only 16 per cent of clinics looked at the sperm under the recommended microscope magnification and only 30 per cent counted enough sperm on the microscope slide to make the measurement a robust one.
The WHO recommends at last 200 sperm have to be examined to make an assessment of morphology but the majority of clinics in the survey were looking at 100 or less.
Writing in Human Reproduction, the researchers said: “If an assessment is made on fewer than this number, it is entirely plausible that poorly shaped sperm warranting the use of ICSI may be diagnosed, whereas in reality the sample is completely normal.”
Dr Kate Whittington, lecturer in reproduction and development at the University of Bristol who led the research, said: “It is very disappointing that, more than five years after the publication of the guidelines, our survey should find only five per cent of the UK laboratories that responded were compliant with all of the WHO recommendations.”
Dr Allan Pacey, senior lecturer of andrology at the University of Sheffield and a co-author of the report, said: “This is a difficult measurement to perform in the lab, but for so many to ignore the guidelines in such a way increases the probability of finding problems when there really aren't any.
“Couples could be guided towards more costly treatments such as ICSI whereas less sophisticated treatments might have been just as effective.”