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IUI success is dependant on motile sperm count threshold

19 April 2021
Appeared in BioNews 1091

Researchers have identified a sperm count threshold which optimises the chance of intrauterine insemination (IUI) resulting in pregnancy.

The retrospective study found that while the highest rate of pregnancy per cycle was achieved with a total motile sperm count of over 9 million, pregnancy also occurred using sperm samples with a total sperm motility count of less than 250,000.  

'Since the decline in pregnancy is gradual and continuous, there is no specific threshold above which IUI should be recommended,' the authors said in the study published in the journal Fertility and Sterility

IUI is a commonly used fertility treatment for couples experiencing unexplained subfertility. Sperm samples from the male partner are 'washed' in a solution which attracts the most motile sperm cells, and these are then placed directly into the female partner's uterus. The process is less costly and less invasive in comparison to IVF.

Research examining factors which predict the likelihood of a successful pregnancy following IUI therapy have largely focused on female factors such as age or the number of mature ovarian follicle. Studies relating to male sperm count or motility in relation to IUI success have been small in scale with varying results, and until now, there has not been a clear optimum threshold for sperm count following preparation. 

Now, in the largest study to examine the relationship between postwash total motile sperm count and IUI success, researchers have found that a count of over nine million provides the best chance of achieving a pregnancy. 

The retrospective study reviewed the sperm count, from fresh or frozen samples, and subsequent outcome from over 37,000 IUI patients who collectively underwent 92,471 insemination cycles at a single fertility institution between 2002 and 2018. After adjusting for female age, body mass index (BMI) and ovarian stimulation protocol, results showed that the highest rate of pregnancies occurred with a total motile sperm count of over nine million. This count was associated with a pregnancy rate per cycle of 16.7 percent. 

The authors found that the rate of pregnancy 'gradually declined' as the total motile sperm count fell below this threshold. Patients who were aged 35 and above had significantly lower pregnancy rates per cycle. 

However, the study also noted that pregnancies did arise in cases with a total motile sperm count of as low as 250,000, but this was a rare event. Therefore, the authors emphasise that they were not proposing a particular threshold be used but that postwash total motile sperm count may serve a 'unique value' in helping to improve success rates of IUI and guide decisions. They added further research was needed to determine whether other factors influence the outcome of this treatment. 

Clarifying the relationship between total motile sperm counts and intrauterine insemination pregnancy rates
Fertility and Sterility |  17 February 2021
Motile sperm count in the prediction of IUI success
Focus on Reproduction |  13 April 2021
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