A standard semen analysis counts sperm and looks at how they swim and what they look like. It cannot see the DNA inside. Sperm can look normal under the microscope and still carry single- or double-strand breaks in their DNA.1
Most ejaculates contain some sperm with fragmented DNA, and levels can be particularly raised in some subfertile men.1 Damage can arise while sperm are being made, as they travel and are stored, or after ejaculation. Oxidative stress is the most commonly proposed driver.
Several different tests exist, including SCSA (sperm chromatin structure assay), TUNEL, SCD (sperm chromatin dispersion) and Comet, and they do not all perform the same way.2 Always compare results from the same test and, ideally, the same lab.
What is a normal DNA fragmentation index?
There is no universal cut-off, because each test has its own scale. On the SCSA test, 30% or more has long been treated as a level linked with poorer fertility.
That 30% figure traces back to a 1999 study of couples trying to conceive. Among those who conceived within the first three months, 84% of the men had values below 15%, and none had 30% or more.3
Other assays use different thresholds, so a number on its own means little unless you know which method produced it and what that lab considers high.
Does sperm DNA fragmentation affect pregnancy?
High levels are linked with a higher chance of miscarriage. The evidence that testing reliably predicts whether IVF or ICSI will work is weaker.
A 2012 meta-analysis of 16 cohort studies (2,969 couples) found miscarriage risk roughly doubled when sperm DNA damage was high (risk ratio 2.16), with the strongest association seen for the TUNEL test.1
A 2016 meta-analysis of 30 studies was more cautious. It found that current tests had limited ability to predict pregnancy after assisted reproduction, and concluded there was insufficient evidence to recommend routine testing for couples undergoing IVF or ICSI.2
Can high sperm DNA fragmentation be lowered?
Sometimes. Treating a clear cause, particularly a varicocele, has the best evidence; general health changes are sensible but less well studied.
The strongest evidence comes from varicocele repair. A 2021 meta-analysis of 19 studies (1,070 men) found fragmentation fell by about 7 percentage points after surgery, with larger drops in men who started with high levels.4
Other factors a doctor may ask about include smoking, heat exposure, infection, recent fever and weight. Changes to these are low risk, and because sperm take weeks to develop, any retest should allow time for a new cohort to come through. See our guides to lifestyle factors that affect male fertility and guide to supplement ingredients and the research.
Who should consider a DNA fragmentation test?
It is most often discussed after recurrent miscarriage, repeated failed IVF or ICSI, or unexplained infertility. It is not a routine first test.
Robinson and colleagues suggested testing could be considered for couples experiencing recurrent pregnancy loss.1 Before paying for a test privately, ask the clinic which assay they use, what threshold they apply and, crucially, what they would do differently depending on the result. If the answer is nothing, the test may not be worth it for you.
If you have had recurrent miscarriages or failed cycles, talk to your fertility doctor about whether male factors, including DNA fragmentation, have been properly assessed.
Common questions
Can a normal semen analysis hide high DNA fragmentation?
Yes. A standard analysis measures count, movement and shape, not DNA integrity, so a man can have normal results and still have high fragmentation.
Is sperm DNA fragmentation a genetic condition?
No. It refers to physical breaks in the DNA strands of individual sperm, not an inherited mutation. Levels can change over time, and can fall after treating an underlying cause such as a varicocele.4
How is sperm DNA fragmentation tested?
From a semen sample sent to a lab that runs a specialist assay such as SCSA, TUNEL, SCD or Comet. Results are given as a percentage of sperm with damaged DNA, and each assay has its own thresholds.2
Read more on this
Lifestyle factors that affect male fertility: a practical guide
Supplement ingredients for men’s sexual health: what the research shows
Sources
- Robinson L, Gallos ID, Conner SJ, et al. The effect of sperm DNA fragmentation on miscarriage rates: a systematic review and meta-analysis. Hum Reprod. 2012;27(10):2908-17. PubMed
- Cissen M, van Wely M, Scholten I, et al. Measuring Sperm DNA Fragmentation and Clinical Outcomes of Medically Assisted Reproduction: A Systematic Review and Meta-Analysis. PLoS One. 2016;11(11):e0165125. PubMed
- Evenson DP, Jost LK, Marshall D, et al. Utility of the sperm chromatin structure assay as a diagnostic and prognostic tool in the human fertility clinic. Hum Reprod. 1999;14(4):1039-49. PubMed
- Lira Neto FT, Roque M, Esteves SC. Effect of varicocelectomy on sperm deoxyribonucleic acid fragmentation rates in infertile men with clinical varicocele: a systematic review and meta-analysis. Fertil Steril. 2021;116(3):696-712. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.