Sperm DNA fragmentation (SDF) means there are breaks in the genetic material carried by sperm. A higher level is associated with lower pregnancy rates or pregnancy loss in some groups, but it is a risk marker - not a diagnosis of infertility, proof of what caused a loss, or a verdict on whether pregnancy is possible.

Different laboratories measure SDF in different ways, and there is no universal percentage that separates "fertile" from "infertile." A standard semen analysis remains the usual first male fertility test. SDF testing is an additional test that may help in selected situations.

What is sperm DNA fragmentation?

A sperm cell carries tightly packed DNA that contributes half of an embryo's genetic material. Fragmentation refers to single- or double-strand breaks in that DNA. The damage may develop while sperm are being produced, while their DNA is being packaged, or later through oxidative stress.

Many reports summarize the finding as a DNA fragmentation index (DFI). The exact meaning of that number depends on the test method. DFI is not always a directly comparable "percentage of broken DNA," and a value from one assay should not be compared with a value from another as if they used the same scale.

Sperm DNA fragmentation vs. semen analysis

A standard semen analysis and an SDF test answer different questions.

	Standard semen analysis	Sperm DNA fragmentation test
What it examines	Semen volume, sperm concentration, total count, motility, morphology and other routine findings	Damage or susceptibility to damage in sperm DNA, using a specific laboratory assay
Usual role	First-line male fertility test	Additional test for selected clinical situations
Main limitation	Does not directly assess sperm DNA integrity	Does not replace semen analysis or predict an individual pregnancy outcome

It is possible to have semen parameters within the laboratory's reference ranges and still have an elevated SDF result. The reverse is also possible. Neither test should be interpreted alone.

What can cause high sperm DNA fragmentation?

SDF is not one disease with one cause. Research points to three broad pathways: incomplete DNA packaging as sperm mature, abnormal cell-death processes during sperm production, and oxidative stress that damages sperm after they form.

Factors associated with higher SDF include:

Clinical varicocele: Enlarged veins around the testicle can raise temperature and oxidative stress. A clinician must examine you to distinguish a palpable varicocele from an incidental imaging finding.
Smoking and some toxic exposures: Tobacco smoke and certain occupational or environmental exposures are associated with higher DNA damage in observational studies.
Age: SDF tends to rise with paternal age, but there is no single birthday when a result suddenly becomes abnormal.
Metabolic or testicular health problems: Diabetes or impaired glucose control, testicular disease, and gonadotoxic treatment can matter in an individual history.
Inflammation, infection, fever or heat: A recent illness, reproductive-tract inflammation, and substantial heat exposure may affect a result. Infection should be diagnosed rather than assumed.
Collection and handling: Abstinence time, whether the full sample was collected, transport, processing delay, and freezing can change a measurement.

A 2023 systematic review of 190 studies found associations with factors including varicocele, smoking, pollution, impaired glucose tolerance and older paternal age. The studies were mostly observational and varied widely, so an association does not prove what caused one person's result. In the same review, the main pooled analyses did not show a significant difference for body mass index or alcohol alone. Review the study on SDF risk factors.

SDF has no specific symptom you can see or feel. Infertility, pregnancy loss or an unexpected treatment outcome may prompt evaluation, but only a laboratory assay can measure fragmentation.

How does sperm DNA fragmentation affect fertility?

Higher SDF is associated with poorer reproductive outcomes in some studies, but it is not a stand-alone fertility test. Both partners' ages and health, the SDF assay, the treatment used, and the outcome being measured all affect the result.

Situation	What the evidence supports	What it does not prove
Natural conception and IUI	Higher SDF is associated with a lower chance of pregnancy in some groups	That natural pregnancy is impossible above a particular DFI
Recurrent pregnancy loss	Men in couples with recurrent loss have higher average SDF in meta-analyses	That SDF caused a particular miscarriage
IVF	Elevated SDF is associated with lower clinical pregnancy in some analyses	That one result can predict whether a cycle will work
ICSI	Some associations appear smaller for clinical pregnancy, but pregnancy-loss findings remain concerning and evidence quality is limited	That injecting one sperm into an egg repairs or bypasses DNA damage

The link with pregnancy loss is more consistent than the ability to predict pregnancy or live birth. A 2024 umbrella review called the SDF-recurrent-loss association "highly suggestive," while rating the methods in the underlying reviews low or very low quality. Read the umbrella review.

For assisted reproduction, a 2026 umbrella meta-analysis found associations with clinical pregnancy and pregnancy loss, but live-birth evidence remained limited and inconsistent. ICSI may overcome some barriers to fertilization; it does not test or repair the DNA inside the selected sperm. Read the assisted-reproduction review.

Who should consider sperm DNA fragmentation testing?

SDF testing is not a routine first step for everyone. The AUA/ASRM male infertility guideline, amended in 2024, says clinicians should not recommend it in the initial infertility evaluation because evidence has not shown that routine testing changes outcomes.

Testing may be discussed when the result could change a couple's next decision. Examples include:

otherwise unexplained recurrent pregnancy loss;
unexplained infertility after the standard evaluation;
repeated assisted-reproduction failure in selected cases; or
a clinical risk factor, such as a palpable varicocele, when a reproductive urologist or andrologist believes the result would affect management.

Guidelines are not identical. The current European Association of Urology guideline recommends testing for recurrent loss, assisted-reproduction failure or unexplained infertility. The 2026 ASRM recurrent pregnancy loss opinion is narrower: testing may be considered in otherwise unexplained recurrent miscarriage or recurrent loss with infertility, while more research is needed to show that treatment improves pregnancy outcomes. For recurrent implantation failure specifically, ASRM's 2026 opinion says the evidence is insufficient to recommend SDF testing.

Before ordering the test, ask what you and your clinician would do differently with the result.

How is sperm DNA fragmentation tested?

The World Health Organization's 2021 laboratory manual describes SDF as an extended semen examination. Four main assay families are used in clinical care and research.

Test	What it measures	Interpretation caution
SCSA (sperm chromatin structure assay)	Uses flow cytometry to measure how susceptible sperm chromatin is to acid-induced denaturation	Indirect measure; produces a method-specific DFI and sometimes a separate chromatin-maturity measure
TUNEL	Labels the exposed ends of DNA strand breaks	Direct measure, but results depend on protocol, instrument and laboratory cutoff
SCD (sperm chromatin dispersion or halo test)	Scores the pattern formed after sperm chromatin is processed	Indirect measure with method- and reader-dependent thresholds
Comet assay	Uses electrophoresis to visualize DNA migration from individual sperm cells	Direct measure; alkaline and neutral versions and their scoring systems are not interchangeable

These tests do not share one universal "normal DFI." Published decision points vary by assay, laboratory and the outcome being studied. For example, the European guideline cites an SCSA DFI around 25% as associated with lower natural-conception or IUI pregnancy rates. That does not make 25% a universal cutoff for TUNEL, SCD or Comet, and it does not mean pregnancy is impossible above it.

How to read a DFI result

Before interpreting the number, check five details:

Assay name: Was the result produced by SCSA, TUNEL, SCD or Comet?
Laboratory reference: Which decision range did that laboratory validate for its method?
Collection conditions: What was the abstinence interval, and was the full sample collected and processed as instructed?
Recent health changes: Was there a fever, significant illness, new medication, treatment or unusual heat exposure?
Clinical context: What did the semen analysis show, and what are both partners' ages, fertility history, pregnancy-loss history and prior treatments?

A high result means the assay found more DNA damage than the laboratory's comparison range. It does not mean every sperm is damaged, that a future child will have a genetic condition, or that natural conception cannot happen.

If a result is surprising or would change treatment, a clinician may suggest repeating it. For a useful comparison, use the same assay and laboratory and follow the same collection instructions. There is no universal retest interval. About three months is a common checkpoint after a longer-term medical or lifestyle change because it covers roughly one sperm-development cycle, while other situations call for a different timeline.

What can you do after a high DFI result?

Use the result to look for a contributor that can be treated, reduce avoidable risks, and choose the next step that makes sense for both partners.

1. Review the result with the right clinician

A reproductive urologist or andrologist can review the report, examine for a clinical varicocele, and decide whether hormonal, metabolic, infection-related or other testing is appropriate. Both partners should continue their evaluations in parallel. Do not start antibiotics for a presumed infection or stop a prescribed medicine on your own.

2. Get the fertility baseline into context

If you have not had a standard semen analysis, that is usually the first missing piece. If it is abnormal, a repeat analysis may be needed because semen parameters vary. A normal analysis does not erase a high SDF result, but the two reports together give a clinician more useful information than either alone.

3. Address plausible reversible factors

Stopping tobacco, avoiding anabolic steroids and non-prescribed testosterone, managing diabetes, reducing meaningful heat or toxic exposures, and treating a diagnosed condition support general reproductive health. A palpable varicocele may warrant a surgical discussion, but repair is not an automatic SDF treatment. Evidence that an intervention lowers DFI is not the same as proof that it improves live birth.

4. Be cautious with antioxidants and fertility supplements

No antioxidant, vitamin, herb or commercial blend is proven to normalize DFI or improve live birth for every man. In the multicenter randomized MOXI trial, an antioxidant combination did not improve sperm DNA integrity, semen quality or live birth compared with placebo. A clinician can help you weigh a documented deficiency, dose, interactions and cost instead of treating a lab number with a large supplement stack.

5. Make collection and treatment decisions with the clinic

Shorter abstinence can lower SDF in some samples, but it can also lower semen volume and sperm concentration. Do not improvise the interval before diagnostic testing, IUI or IVF; follow the receiving laboratory's instructions.

If assisted reproduction is being considered, the clinic may discuss ICSI, sperm-selection methods or, in highly selected cases, surgically retrieved sperm. None is a guaranteed fix for DNA fragmentation. Testicular sperm requires a procedure and can be used only with ICSI; European guidance still describes this approach as experimental for high ejaculated SDF.

A practical first step

Review a high DFI in context. Start with a complete fertility history, a standard semen analysis, and a clinician who can interpret both partners' results together.

Hera helps arrange a physician-signed requisition and lets you find a local laboratory for a standard semen analysis. If you already have a semen analysis report, you can upload it for a free plain-English interpretation. Hera does not replace a reproductive urologist or diagnose the cause of an elevated SDF result.

Sperm DNA Fragmentation: Causes, Tests and Fertility