What It Means When Your Sperm Count Is Low but Motility Is Normal

Key takeaways:

• A sperm concentration below the WHO 6th Edition threshold of 16 million per milliliter alongside normal progressive motility of 30% or higher is a specific, real pattern that shows up in only about 4% of infertile men, far less often than combined abnormalities (Candela et al., PLOS ONE, 2021).
• Sperm concentration is the most variable semen parameter from one sample to the next, and test-retest research has found a single result needs to shift by more than half to reliably reflect a real change rather than normal biological noise (Alvarez et al., Human Reproduction, 2003; Keel, Fertility and Sterility, 2006).
• Natural conception odds decline gradually as concentration drops rather than falling off a cliff right at the WHO threshold, and for couples pursuing IUI, a total motile sperm count of roughly 5 to 9 million is where success rates begin to plateau (Bonde et al., The Lancet, 1998; Tan et al., Journal of Assisted Reproduction and Genetics, 2014; Muthigi et al., Fertility and Sterility, 2021).

Getting a semen analysis back with one number flagged low and the rest looking fine is a specific, confusing kind of result. Most men expect a report to either come back clean or come back as a uniform mess, so seeing concentration flagged while motility, morphology, and volume all sit inside normal range reads as contradictory. It is not contradictory. Concentration and motility are produced by different parts of the reproductive system and measure different things, so one can fall out of range while the other holds steady. Here is what that specific combination actually means, how common it really is, and what is worth checking before assuming the worst or dismissing it entirely.

What does it mean when sperm count is low but motility is normal?

It means the testes are producing fewer sperm than the WHO 6th Edition reference threshold of 16 million per milliliter, or the total count in the ejaculate is below 39 million, but the sperm that are present move normally, at or above the 30% progressive motility threshold set by the same WHO 6th Edition reference data (Campbell et al., Andrology, 2021). Concentration is the number of sperm in each milliliter of semen. Total count is concentration multiplied by volume, the number of sperm in the whole ejaculate. Progressive motility is the share of sperm swimming forward in a relatively straight line, which is the kind of movement needed to travel through the female reproductive tract and reach an egg. A man can be short on the first two numbers while the third one is completely normal, because low count reflects how many sperm are being made and released, while motility reflects how well the sperm that did make it are functioning.

This exact pattern, sometimes described in research as isolated oligozoospermia, is real but less common than people assume. A 2021 study of 1,824 infertile men and 103 fertile controls found low concentration on its own, with motility and shape both normal, in only 4.1% of infertile men. By comparison, isolated low motility alone showed up in 13.9% of cases, isolated abnormal shape alone in 11.9%, and two or more parameters out of range together in 54.7% of cases (Candela et al., PLOS ONE, 2021). In plain terms, most men with an abnormal semen analysis have more than one number affected at once. A low count sitting by itself, with everything else normal, is the less typical version of an abnormal result, and that is worth knowing before assuming a low count automatically means broader dysfunction. Our deep dive on sperm concentration covers what drives the number generally and what the supplement evidence looks like. This article is about the narrower and more specific question of what it means when that one number is off while motility is not.

What actually causes an isolated low sperm count?

Several things can lower concentration specifically without touching motility, and knowing which one applies changes what you do next.

Varicocele, a cluster of enlarged veins in the scrotum, appears to hit concentration harder than it hits motility. A cross-sectional study of over 7,000 healthy young European men found a clear dose-response relationship: men with a grade 3 varicocele, the largest and most visible kind, had sperm concentration less than half that of men without one, along with higher FSH and LH and lower inhibin B, a hormone made in the testes that reflects how well sperm-supporting cells are functioning (Damsgaard et al., European Urology, 2016). Our varicocele explainer covers what the condition is, how it is diagnosed, and what repair can and cannot do.

How the sample was collected also matters more for concentration than people expect. The sperm-rich portion of an ejaculate comes out first, so losing part of that first portion during collection, whether from an awkward collection setup or a rushed process, will lower the counted concentration without touching the motility of the sperm that were actually captured. A review on semen collection technique put it plainly: losing the first portion of the ejaculate will significantly affect the accuracy of the sperm number measured, even though it says nothing about whether the man's own sperm production is actually low (Aziz, Clinics, 2013). Abstinence length before the test matters too. In men whose baseline concentration is already low, one large retrospective study of nearly 9,500 samples found sperm motility was actually highest after just one day of abstinence, while in men with normal concentration, sample quality tended to decline somewhat after 11 to 14 days without ejaculation (Levitas et al., Fertility and Sterility, 2005). The general direction from this and related abstinence research is that volume and concentration tend to rise over the first several days of abstinence and level off after that, which is part of why most labs ask for two to seven days of abstinence before a sample, specifically to avoid an artificially low or high reading.

Hormonal patterns are the other major branch, and they point toward genuinely different next steps. Guidelines recommend a hormone panel, including FSH and testosterone, whenever concentration falls below about 10 million per milliliter (AUA and ASRM, Diagnosis and Treatment of Infertility in Men, 2020, amended 2024). An elevated FSH alongside low concentration usually points to a problem in the testes themselves, since FSH rises when the brain is trying harder to stimulate sperm production that is not responding. Low or normal FSH alongside low testosterone points toward a signaling problem further up the chain, in the brain rather than the testes. Our FSH article and LH article both walk through how to read that pattern in full.

Is one low result enough to worry about?

Not on its own, and concentration specifically is the parameter least trustworthy from a single sample. A study following 20 sperm donor candidates over ten weeks of repeated samples found concentration had the highest variation, both from week to week in the same man and from man to man, of any semen parameter measured. The researchers calculated what they called a critical difference, the minimum change needed before a shift in a result can be considered a real biological change rather than normal noise: 77.8% for concentration, compared with 49.2% for progressive motility and 34.4% for vitality (Alvarez et al., Human Reproduction, 2003). A separate study comparing 74 infertile men and 65 sperm donors across thousands of ejaculates found the within-person variation in sperm count was the highest of any parameter tracked, and concluded that a minimum of three samples is needed before classifying a man's fertility status with any confidence (Keel, Fertility and Sterility, 2006). In practice, this means a single low concentration reading, especially one close to the WHO threshold rather than dramatically below it, is not something to act on by itself. A repeat test, done under similar conditions and abstinence timing, is the reasonable next step before drawing any conclusion.

Does this still allow natural conception?

Often yes, and the honest answer is more encouraging than a strict pass or fail reading of the WHO threshold suggests. A study that followed 430 couples for up to six menstrual cycles after they stopped using contraception found an overall pregnancy rate of 59.5%. Men with sperm concentration at or above 40 million per milliliter had a 65.0% pregnancy rate over that window, compared with 51.2% for men below 40 million per milliliter, and the probability of conception rose steadily with concentration up to about 40 million per milliliter before leveling off (Bonde et al., The Lancet, 1998). The same study found sperm shape was an independent predictor of pregnancy regardless of concentration, while motility and semen volume added comparatively little extra predictive information once concentration and shape were accounted for.

Two things are worth taking from this. First, the steepest part of the decline in conception probability sits well below the WHO reference floor of 16 million per milliliter, not right at it, so a concentration just under that threshold is a meaningfully different situation from a concentration of 2 or 3 million per milliliter. Second, normal motility genuinely helps here. A man with low concentration and normal motility is not the same as a man with low concentration and poor motility, even though both would be flagged as abnormal on the same report. We are more cautious about one thing this data cannot tell you: it predates routine sperm DNA fragmentation testing, which a standard semen analysis does not measure and which can meaningfully affect the picture even when concentration and motility both look reasonable. Our DNA fragmentation article covers what that additional number can add to this picture.

What does this mean for IUI, IVF, or ICSI?

If natural conception has not happened after a reasonable trying period, the number that matters most for planning fertility treatment is not concentration by itself but total motile sperm count, often shortened to TMSC. TMSC combines semen volume, concentration, and the percentage of motile sperm into a single figure representing roughly how many moving sperm are actually available in an ejaculate, and it is usually recalculated after the sample is processed, or washed, in a lab.

A study of 6,871 IUI cycles across 3,421 patients found pregnancy rates climbed with post-wash TMSC: 8.1% when TMSC was under half a million, up to 18.4% in the 5 to 10 million range, and 18.8% above 10 million, with the odds of pregnancy roughly doubling once TMSC reached 5 million or higher (Tan et al., Journal of Assisted Reproduction and Genetics, 2014). A larger study of 92,471 IUI cycles across 37,553 patients found pregnancy rates decline gradually as TMSC drops below about 9 million, with no further meaningful relationship to outcome above that point, and importantly found no sharp cutoff anywhere in the data. The commonly cited 5 to 10 million range is where the curve is steepest, not a hard line that separates success from failure (Muthigi et al., Fertility and Sterility, 2021). A man with a low concentration but normal motility and reasonable semen volume can still land in a workable TMSC range for IUI. A very low TMSC, well under the 5 million range even after processing, is generally where the conversation shifts toward IVF, and where severe cases move toward ICSI, a technique where a single sperm is injected directly into an egg.

What we are more skeptical about

Supplements come up quickly in any conversation about a low sperm count, and the evidence for concentration specifically is genuinely better than for some other parameters. A meta-analysis of randomized trials found omega-3 fatty acid supplementation raised sperm concentration by an average of 10.98 million per milliliter, and CoQ10 raised it by an average of 10.22 million per milliliter across the trials reviewed (Salas-Huetos et al., Advances in Nutrition, 2018). That is a real, replicated signal, and we think it is worth knowing about. But it does not change the analysis in this article. None of that evidence addresses whether a man's specific pattern, isolated low count with normal motility, is being driven by a varicocele, a collection or abstinence issue, or a genetic cause, and supplements do not fix any of those three things. The most comprehensive recent review of male fertility supplements, covering 50 randomized trials and more than 4,800 participants, found no statistically significant effect of any supplement on pregnancy or live birth rates, even where individual sperm parameters improved (Henriksen et al., Nutrients, 2025). We are not dismissing the concentration data. We are saying it answers a narrower question than the one most men actually have, which is whether taking something will meaningfully change their odds of becoming a father. On the current evidence, it has not been shown to.

What to actually do next

Start by repeating the test rather than reacting to a single number. Use the abstinence window your lab recommends, usually two to seven days, keep it consistent between the two samples, and make sure the full ejaculate is collected since losing the first portion alone can make concentration look artificially low. Ask for a hormone panel alongside the repeat semen analysis, since FSH, LH, and testosterone read together tell you whether this is a testicular problem or a signaling problem higher up, and that distinction changes what a urologist will recommend. Ask specifically about a varicocele exam if one has not been done, since it is common, correctable, and has a clear, disproportionate effect on concentration compared with motility. If you are actively pursuing IUI, ask your clinic for your actual post-wash TMSC rather than relying on the raw concentration number alone, since that combined figure is what actually predicts treatment success. And know when to escalate: AUA and ASRM guidelines recommend a full male fertility evaluation after 12 months of trying without success, shortened to 6 months if the female partner is 35 or older, and that evaluation should happen alongside the female partner's workup, not after it (AUA and ASRM, Diagnosis and Treatment of Infertility in Men, 2020, amended 2024).

Our take

An isolated low sperm count with normal motility is a specific, less common version of an abnormal semen analysis, and it is not the same problem as a broadly poor result across every parameter. We know concentration is the least reliable number on a single test, so a repeat sample is genuinely worth doing before reacting. We know several distinct and identifiable causes, a varicocele, a collection issue, an abstinence timing issue, or a hormonal pattern, can each produce this exact combination, and they call for different next steps. We know the decline in natural conception odds as concentration drops is gradual rather than a cliff at the WHO threshold, and that normal motility is a genuinely favorable sign sitting alongside the low count, not a number that cancels it out.

What we do not know, and will not pretend to, is whether any single intervention will resolve a specific man's case, because that depends entirely on which of several possible causes is actually driving his number. The honest path is to confirm the result, identify the cause, and act on the one that actually applies, rather than assuming the worst from one flagged line on a report or ignoring it because three other numbers looked fine.

FAQ

Can a low sperm count with normal motility still lead to pregnancy?
Yes, often. Pregnancy rates decline gradually as concentration drops rather than falling sharply at the WHO threshold of 16 million per milliliter, and a cohort study found men just below higher concentration bands still conceived at meaningful rates over repeated cycles (Bonde et al., The Lancet, 1998).

What is isolated oligozoospermia?
It is the term researchers use for a low sperm concentration that occurs while progressive motility and sperm shape both remain within the normal range. It is a real but relatively uncommon pattern, found in about 4.1% of infertile men in one study, compared with over half of infertile men who have two or more abnormal parameters together (Candela et al., PLOS ONE, 2021).

How many semen analyses should I get before trusting a low count result?
At least two, and research supports three where possible. Sperm concentration is the most variable parameter from sample to sample, and studies recommend multiple tests before drawing conclusions about a man's fertility status (Alvarez et al., Human Reproduction, 2003; Keel, Fertility and Sterility, 2006).

Does a varicocele specifically cause low sperm count rather than low motility?
Varicocele affects both, but the evidence shows a stronger and more direct relationship with concentration than with motility or shape, particularly at higher varicocele grades (Damsgaard et al., European Urology, 2016).

What total motile sperm count is good enough for IUI?
Success rates rise steadily up to a post-wash total motile sperm count of roughly 5 to 9 million and level off above that, with no sharp cutoff. Very low counts after processing generally shift the conversation toward IVF or ICSI instead (Tan et al., Journal of Assisted Reproduction and Genetics, 2014; Muthigi et al., Fertility and Sterility, 2021).

References

1. Campbell MJ, Lotti F, Baldi E, et al. Distribution of semen examination results 2020, a follow up of data collated for the WHO semen analysis manual 2010. Andrology. 2021;9(3):817-822. https://pubmed.ncbi.nlm.nih.gov/33528873/
2. Boitrelle F, Shah R, Saleh R, et al. The Sixth Edition of the WHO Manual for Human Semen Analysis, a Critical Review and SWOT Analysis. Life. 2021;11(12):1368. https://pmc.ncbi.nlm.nih.gov/articles/PMC8706130/
3. Candela L, et al. Correlation among isolated teratozoospermia, sperm DNA fragmentation and markers of systemic inflammation in primary infertile men. PLOS ONE. 2021;16(6):e0251608. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251608
4. Damsgaard J, et al. Varicocele Is Associated with Impaired Semen Quality and Reproductive Hormone Levels, a Study of 7035 Healthy Young Men from Six European Countries. European Urology. 2016;70(6):1019-1029. https://pubmed.ncbi.nlm.nih.gov/27423503/
5. Aziz N. The sperm-rich ejaculate fraction and the accuracy of semen analysis. Clinics. 2013;68(Suppl 1):111-118. https://pmc.ncbi.nlm.nih.gov/articles/PMC3583176/
6. Levitas E, et al. Relationship between the duration of sexual abstinence and semen quality, analysis of 9,489 semen samples. Fertility and Sterility. 2005;83(6):1680-1686. https://pubmed.ncbi.nlm.nih.gov/15950636/
7. American Urological Association and American Society for Reproductive Medicine. Diagnosis and Treatment of Infertility in Men, AUA and ASRM Guideline. 2020, amended 2024. https://www.auanet.org/guidelines-and-quality/guidelines/male-infertility
8. Alvarez C, et al. Biological variation of seminal parameters in healthy subjects. Human Reproduction. 2003;18(10):2082-2088. https://pubmed.ncbi.nlm.nih.gov/14507825/
9. Keel BA. Within and between subject variation in semen parameters in infertile men and normal semen donors. Fertility and Sterility. 2006;85(1):128-134. https://pubmed.ncbi.nlm.nih.gov/16412742/
10. Bonde JP, et al. Relation between semen quality and fertility, a population-based study of 430 first-pregnancy planners. The Lancet. 1998;352(9135):1172-1177. https://pubmed.ncbi.nlm.nih.gov/9777833/
11. Tan O, Ha T, Carr BR, et al. Predictive value of postwashed total progressively motile sperm count using CASA estimates in 6871 non-donor intrauterine insemination cycles. Journal of Assisted Reproduction and Genetics. 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC4156954/
12. Muthigi A, et al. Clarifying the relationship between total motile sperm counts and intrauterine insemination pregnancy rates. Fertility and Sterility. 2021;115(6):1454-1460. https://pubmed.ncbi.nlm.nih.gov/33610321/
13. Salas-Huetos A, et al. The Effect of Nutrients and Dietary Supplements on Sperm Quality Parameters, a Systematic Review and Meta-Analysis of Randomized Clinical Trials. Advances in Nutrition. 2018;9(6):833-848. https://pubmed.ncbi.nlm.nih.gov/30462179/
14. Michaelsen MP, Poulsen M, Bjerregaard AA, et al. (co-author Henriksen SG). The Effect of Dietary Supplements on Male Infertility in Terms of Pregnancy, Live Birth, and Sperm Parameters, a Systematic Review and Meta-Analysis. Nutrients. 2025;17(10):1710. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12113742/

Curious what your own concentration, motility, and hormone panel actually look like together? SwimScore Complete measures all of it from home, processed in the same CLIA-certified labs used by fertility clinics.

Fertility clinics: if you want a straightforward way to get patients baseline testing before their first consult, see how SwimScore works with clinics on our clinic page.

This article is for general education and is not medical advice. A specific low sperm count result should be reviewed with a urologist or fertility specialist who can account for your full history.

SwimScore uses CLIA-certified labs for all semen analysis and hormone testing, assessed against WHO 6th Edition clinical thresholds.