How to improve sperm morphology: what the evidence shows.

Sperm morphology is the share of sperm with a normal shape under strict criteria, and the WHO 2021 lower reference limit is 4% (95% CI 3.9 to 4.0). Most sperm in fertile men look abnormal: in one study of men who had fathered a child in the previous five years without fertility treatment, more than half had 3% normal forms or fewer. Morphology on its own is a weak predictor of pregnancy, naturally or with IVF, ICSI or IUI. No supplement has been shown in a large trial to raise it, and the changes linked to better morphology are the ones linked to better semen generally: not smoking, moderate drinking, a healthy weight, regular exercise and keeping the testicles cool. Effects are small, around one or two percentage points, and any change takes about three months to show in a sample.

What morphology means on your report

Morphology is the shape of sperm: the head, the midpiece and the tail. A lab stains the sample, looks at sperm under a microscope and counts how many meet strict criteria for a normal shape, often called Tygerberg or Kruger criteria [6]. The result is a percentage of normal forms.

The WHO 2021 manual puts the lower reference limit at 4% normal forms, with a 95% confidence interval of 3.9 to 4.0 [1][2][3]. That is the 5th centile of men whose partners conceived within a year, so 95% of those men were at or above it. It is a reference point, not a line between fertile and infertile, and the manual works from the numbers rather than from labels like teratozoospermia [23]. As the manual puts it, "for an individual patient, a semen analysis is never prognostic of fertility, as it is the fertility potential of the couple that defines them as fertile or subfertile" [1].

Is it normal for most sperm to look abnormal?

Yes. A result of 4% means 96 in every 100 sperm were scored as abnormal, and that is still within the reference range. In a US clinic study of 68 men seen before a vasectomy, all of whom had fathered a child in the previous five years without fertility treatment, 55.9% had 3% normal forms or fewer, and two had 0% [4]. Count and motility were normal in over 90% of them.

Morphology is also the hardest semen value to measure consistently. A survey of 536 US labs found that only 60% stated on the report which criteria they used, and earlier proficiency testing had found coefficients of variation for morphology ranging from 15% to 93% between labs [5]. A 3% at one lab and a 5% at another may not be a real difference.

How much morphology matters for getting pregnant

Less than it once seemed. The best-known comparison, by Guzick and colleagues in the New England Journal of Medicine, studied 765 men in infertile couples and 696 fertile men. Below 9% normal forms fell in that study's subfertile range and above 12% in its fertile range, with an indeterminate zone between, but the authors found "extensive overlap between the fertile and the infertile men" and wrote that "none of the measures ... are diagnostic of infertility" [7]. Those percentages come from that study's own scoring and do not map onto the WHO 4% limit.

For treatment, the evidence points the same way:

• IVF and ICSI. A meta-analysis covering 2,853 IVF or ICSI cycles found that isolated teratozoospermia, meaning low morphology with normal count and motility, "was not associated with a statistically significantly decreased probability of pregnancy" [8].
• IUI. A meta-analysis of 41,018 IUI cycles found pregnancy rates of 14.2% per cycle above 4% normal forms and 12.1% at or below it, a difference that was not statistically significant. The authors concluded that abnormal morphology alone "should not exclude couples from attempting intrauterine insemination" [9].

A 2018 review put it plainly: "clinicians should not rely on percentage thresholds for normal sperm when deciding on which ART to opt for" [10]. The AUA and ASRM guideline says semen results "are of greatest clinical significance when multiple SA abnormalities are present", SA meaning semen analysis [11].

When morphology matters on its own

In a few rare conditions where nearly every sperm carries the same specific defect. The main two are globozoospermia, where the heads are round and lack the acrosome, the cap a sperm uses to get into an egg, and macrozoospermia, where the heads are unusually large. Both usually have a genetic cause: deletion of the DPY19L2 gene accounts for most globozoospermia, and two recurrent mutations in AURKC for almost all macrozoospermia [12]. The AUA and ASRM guideline names complete globozoospermia as one of the few semen findings that on its own points to infertility [11]. These are diagnosed by a specialist, not from one percentage on a report.

What is linked to better or worse morphology

Most of this evidence is observational, so it shows links rather than proof that changing a habit changes morphology. The differences are small, usually one or two percentage points.

• Smoking. A meta-analysis of 20 studies and 5,865 men found smokers had 1.37 percentage points fewer normal forms on average, with larger differences in moderate and heavy smokers [13]. More in our smoking and vaping guide.
• Alcohol. Across 15 studies and 16,395 men, men who drank little or nothing had 1.87 points more normal forms. The gap was clearest between daily and occasional drinkers, and moderate drinking did not appear to affect semen [14]. See alcohol and sperm.
• Weight. A 2025 meta-analysis of 8,443 men found normal-weight men had 0.67 points more normal forms than men with obesity [15]. In a review of weight-loss studies, lifestyle programs were followed by about 0.59 points more normal forms, on low-certainty evidence [16]. See weight and sperm.
• Exercise. A meta-analysis of six randomized trials with 1,637 men found physical exercise was linked to better normal morphology [17]. This is some of the only trial-level evidence for a lifestyle change here. See exercise and cycling.
• Heat and varicocele. NICE notes an association between raised scrotal temperature and lower semen quality [3]; our heat guide covers what that means day to day. In men with a varicocele that can be felt and abnormal semen, a pooled analysis of before-and-after results from 17 studies found about 3 points more normal forms after surgical repair [18].
• Diet. A systematic review of observational studies linked diets with more fish, seafood, poultry, vegetables, fruit and cereals to better semen quality, and more processed meat, full-fat dairy and soy foods to worse, while noting that observational studies "may prove associations but not causation" [19]. See diet for sperm health.

Do supplements improve morphology?

The best trials say no. In the MOXI trial, 171 of the 174 men with male factor infertility were randomly assigned an antioxidant blend or a placebo, and there were "no statistically significant differences" in morphology or motility after three months [20]. In the FAZST trial, 2,370 men took folic acid and zinc or a placebo; normal forms were 5.7% against 6.0%, and live births 34% against 35% [21]. A 2022 Cochrane review of 90 trials found antioxidants may raise live birth rates, but on very low-certainty evidence, and the effect went away when trials at high risk of bias were removed [22]. There is more in our supplements guide.

How long a change takes to show

Sperm take about 74 days to develop, a figure usually traced to Heller and Clermont's 1964 work; their 1963 estimate was about 64 days [24][25]. A change made today would show in a sample around two and a half to three months later. NICE advises a repeat test ideally 3 months after an abnormal result "to allow time for the cycle of spermatozoa formation to be completed", or as soon as possible if very few sperm or none were found [3]. Our 74-day timeline works the dates out from any start date, and when to retest covers the rest.

What to do

• Read morphology alongside count and motility, not on its own. Our semen analysis checker puts every value next to the WHO limit, and the total motile sperm count calculator gives the number that tracks natural conception best.
• If one result is low, ask for a repeat test, ideally about three months later and at the same lab.
• Work on what has the most evidence for semen quality overall: stopping smoking, keeping alcohol moderate, moving toward a healthy weight, exercising regularly and keeping the testicles cool.
• Treat supplements sold to fix morphology with caution. The two largest trials found no improvement.
• If you have been trying for a year, see a GP. NICE advises an earlier referral if your partner is 36 or over, or there is a known cause [3]. Low morphology on its own is not a reason to rule out any treatment.

Common questions

Related guides

• Reading a semen analysis
• Improving motility
• Low sperm count
• Every factor ranked
• TMSC calculator

Sources

1. World Health Organization. WHO laboratory manual for the examination and processing of human semen, sixth edition. 2021.
2. Campbell MJ, et al. Distribution of semen examination results 2020: a follow up of data collated for the WHO semen analysis manual 2010. Andrology, 2021.
3. National Institute for Health and Care Excellence. Fertility problems: assessment and treatment (NG257). 2026.
4. Cheng LG, et al. High rate of isolated teratospermia in a population of fertile men and the questionable clinical utility of sperm morphology. F&S Reports, 2024 (see also the 2025 corrigendum, which revised a table without changing the findings).
5. Keel BA, et al. Lack of standardization in performance of the semen analysis among laboratories in the United States. Fertility and Sterility, 2002.
6. Kruger TF, et al. Predictive value of abnormal sperm morphology in in vitro fertilization. Fertility and Sterility, 1988.
7. Guzick DS, et al. Sperm morphology, motility, and concentration in fertile and infertile men. New England Journal of Medicine, 2001.
8. Hotaling JM, et al. The relationship between isolated teratozoospermia and clinical pregnancy after in vitro fertilization with or without intracytoplasmic sperm injection: a systematic review and meta-analysis. Fertility and Sterility, 2011.
9. Kohn TP, Kohn JR, Ramasamy R. Effect of sperm morphology on pregnancy success via intrauterine insemination: a systematic review and meta-analysis. Journal of Urology, 2018.
10. Kohn TP, Kohn JR, Lamb DJ. Role of sperm morphology in deciding between various assisted reproduction technologies. European Urology Focus, 2018.
11. Schlegel PN, et al. Diagnosis and treatment of infertility in men: AUA/ASRM guideline part I. Fertility and Sterility, 2021.
12. Coutton C, et al. Teratozoospermia: spotlight on the main genetic actors in the human. Human Reproduction Update, 2015.
13. Sharma R, et al. Cigarette smoking and semen quality: a new meta-analysis examining the effect of the 2010 World Health Organization laboratory methods for the examination of human semen. European Urology, 2016.
14. Ricci E, et al. Semen quality and alcohol intake: a systematic review and meta-analysis. Reproductive BioMedicine Online, 2017.
15. Ji F, et al. BMI is associated with sperm quality and sex hormones in men: a meta-analysis. Frontiers in Endocrinology, 2025.
16. Peel A, et al. The effect of obesity interventions on male fertility: a systematic review and meta-analysis. Human Reproduction Update, 2026.
17. Lo Giudice A, et al. Effects of physical activity on fertility parameters: a meta-analysis of randomized controlled trials. World Journal of Men’s Health, 2024.
18. Agarwal A, et al. Efficacy of varicocelectomy in improving semen parameters: new meta-analytical approach. Urology, 2007.
19. Salas-Huetos A, et al. Dietary patterns, foods and nutrients in male fertility parameters and fecundability: a systematic review of observational studies. Human Reproduction Update, 2017.
20. Steiner AZ, et al. The effect of antioxidants on male factor infertility: the Males, Antioxidants, and Infertility (MOXI) randomized clinical trial. Fertility and Sterility, 2020.
21. Schisterman EF, et al. Effect of folic acid and zinc supplementation in men on semen quality and live birth among couples undergoing infertility treatment: a randomized clinical trial. JAMA, 2020.
22. de Ligny W, et al. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews, 2022.
23. Boitrelle F, et al. The sixth edition of the WHO manual for human semen analysis: a critical review and SWOT analysis. Life, 2021.
24. Heller CG, Clermont Y. Kinetics of the germinal epithelium in man. Recent Progress in Hormone Research, 1964.
25. Heller CG, Clermont Y. Spermatogenesis in man: an estimate of its duration. Science, 1963.