Key takeaways:
- A Y-chromosome microdeletion is a small missing stretch of the Y chromosome that carries genes men need to make sperm, and the American Urological Association (AUA) estimates it is present in 8% to 12% of men with non-obstructive azoospermia (no sperm in the ejaculate because the testes are not making enough) and 3% to 7% of men with severe oligospermia (a very low sperm count) (Brannigan et al., Journal of Urology, 2024).
- Which region of the Y chromosome is missing decides the odds: in a Weill Cornell series of 78 men with these deletions, no sperm were found in any man with a complete AZFa or AZFb deletion, while sperm were found in 56% of the 32 men with an isolated AZFc deletion who had testicular sperm extraction or a biopsy (Hopps et al., Human Reproduction, 2003).
- SwimScore reads the research as saying a microdeletion result is a map rather than a verdict, because the deletion is passed to sons conceived with the father's sperm through assisted reproduction (Krausz et al., Andrology, 2014), so genetic counseling belongs before any treatment decision.
Last updated October 20, 2026.
Some men learn the reason for their low or absent sperm count only after a test most people have never heard of. The semen analysis shows almost nothing, the usual explanations do not fit, and a specialist orders a DNA test that looks for missing pieces of the Y chromosome. If the answer is yes, the next question is always the same: can I still have a child, and will my son have the same problem?
Online coverage tends to flatten the answer into either "this means no sperm, ever" or a cheerful success rate with no caveats. The honest answer depends on exactly which piece is missing. This article explains what a Y-chromosome microdeletion is, how common it is, what each region means for sperm retrieval and IVF, what is passed to sons, and where the evidence is thinner than clinic pages suggest.
What Is a Y-Chromosome Microdeletion?
A Y-chromosome microdeletion is a very small piece of the Y chromosome that is missing, in a region that holds genes needed for making sperm. Chromosomes are the packages that carry your genes. Most men have one X and one Y chromosome, and the Y carries the genes that set up the testes and keep sperm production running in adulthood. A microdeletion is too small to show up on a standard chromosome picture (a karyotype), so it takes a separate DNA test to find.
The AUA guideline calls Y-chromosome microdeletions the second most common known genetic cause of male infertility, after Klinefelter syndrome, which we cover in our article on Klinefelter syndrome and male fertility. It explains that deletions happen because the long arm of the Y chromosome is built from large mirror-image repeats, and those repeats can line up wrongly when DNA is copied and shuffled during sperm development, so a stretch gets lost (Brannigan et al., Journal of Urology, 2024). The part of the chromosome that matters is called the AZF region, short for azoospermia factor. It has three sections, named AZFa, AZFb, and AZFc, and each holds genes involved in making sperm.
How Common Are Y-Chromosome Microdeletions?
Y-chromosome microdeletions are found in roughly one in ten men with non-obstructive azoospermia and a smaller share of men with severe oligospermia. The AUA guideline estimates 8% to 12% of men with non-obstructive azoospermia and 3% to 7% of men with severe oligospermia (Brannigan et al., Journal of Urology, 2024). A 2018 review that drew on data from nearly 40,000 Y chromosomes put the global figure at 7.5% of infertile men, and found the rate was lower in European men than in Americans and East Asians (Colaco and Modi, Reproductive Biology and Endocrinology, 2018).
The deletions are also very specific to the problem. The 2013 European guideline notes that no complete AZF deletions have been reported in a large number of men with normal sperm counts. It also lists how the deletions are split: the AZFc deletion makes up about 80% of them, AZFa deletions 0.5% to 4%, AZFb deletions 1% to 5%, and AZFbc deletions 1% to 3% (Krausz et al., Andrology, 2014). That split matters, because AZFc is the region where sperm are most often still found.
A semen result with no sperm or almost none has many possible causes, and a microdeletion is one of them. Our guide to obstructive versus non-obstructive azoospermia explains the others, and our piece on what each semen-analysis label means covers low counts in general.
What Do AZFa, AZFb, and AZFc Mean for Sperm?
A complete deletion of AZFa or AZFb almost always means no sperm can be found, while an AZFc deletion often leaves some sperm production in place. The 2013 European guideline states that a complete AZFa deletion invariably causes Sertoli cell only syndrome and azoospermia. Sertoli cells are the support cells that nurture developing sperm, and in this condition the tubes in the testes contain those support cells but no sperm-making cells at all. Complete AZFb and AZFbc deletions give either that same picture or a sperm-making process that stalls partway, and the guideline says the chance of finding sperm by surgery is virtually zero (Krausz et al., Andrology, 2014).
AZFc deletions behave differently, because they are compatible with some remaining sperm production. A 2021 systematic review found that on testicular biopsy of AZFc-deleted men, 46% showed Sertoli cell only syndrome, 38.2% showed maturation arrest (sperm-making cells that start developing but stop before they finish), and 15.7% showed reduced but present sperm production (Yuen et al., Translational Andrology and Urology, 2021). Some men with an AZFc deletion have a few sperm in the ejaculate. That is why a deletion result does not have one single meaning, and why the region named on the report matters more than the word "deletion" itself.
Can Sperm Still Be Found With a Y-Chromosome Microdeletion?
For AZFc deletions, yes in roughly half of attempts; for complete AZFa or AZFb deletions, essentially never in the published series. Sperm are found by testicular sperm extraction (TESE), a surgical procedure that takes small samples of testicular tissue, or micro-TESE, which uses an operating microscope to pick out the tubes most likely to hold sperm. Any sperm found are then used for ICSI, a form of IVF in which a single sperm is injected directly into an egg.
The Weill Cornell series of 78 men with deletions found that every man with a complete AZFa, AZFb, AZFb plus AZFc, or whole-region deletion was azoospermic, and no sperm were found in any of them by TESE or biopsy. Among men with an isolated AZFc deletion, sperm were found in 75% (9 of 12) by TESE and 45% (9 of 20) on biopsy, 56% overall. Of the 42 men with isolated AZFc deletions, 62% were azoospermic and 38% were severely oligozoospermic, meaning they had a few sperm in the ejaculate (Hopps et al., Human Reproduction, 2003).
The wider literature is consistent but wide. The 2021 review pooled micro-TESE results in AZFc-deleted men from 32 studies and found rates ranging from 13% to 100%, with a mean of 47% (Yuen et al., Translational Andrology and Urology, 2021). The AUA guideline puts it at approximately 50% and states that sperm have not been retrieved by micro-TESE in men with complete AZFa, AZFb, AZFab, or AZFabc deletions, so men with those should not undergo TESE for assisted reproduction (Brannigan et al., Journal of Urology, 2024).
Do Microdeletions Change IVF and ICSI Results?
Possibly, and a recent pooled analysis suggests they do for AZFc deletions, though the evidence is observational. A 2024 systematic review and meta-analysis compared infertile men with and without AZFc deletions using case-control studies, with data from 3,807 men. Sperm retrieval was more likely in men with the deletion, but the difference was not statistically significant (odds ratio 1.82, 95% confidence interval 0.97 to 3.41). Fertilization (odds ratio 0.61), clinical pregnancy (0.61), and live birth (0.54) were all significantly lower in men with AZFc deletions than in men without (Colaco and Modi, Fertility and Sterility, 2024). An odds ratio below 1 means lower odds; a live birth odds ratio of 0.54 means the odds were roughly half as high.
The same analysis found no clear difference in embryo cleavage, blastocyst formation, implantation, or miscarriage. The authors also note that studies of AZFa and AZFb deletions were not available for comparison (Colaco and Modi, Fertility and Sterility, 2024). The 2013 European guideline had described the earlier literature as mostly showing no significant difference in fertilization and pregnancy rates, so this is a place where newer pooled data moves the picture, and not every study agrees (Krausz et al., Andrology, 2014).
Will a Son Inherit the Deletion?
A son conceived with the father's sperm through ICSI is expected to inherit the deletion. The 2013 European guideline says a father's deletion will be obligatorily transmitted to his son, who will then have impaired sperm production, although the exact testicular picture cannot be predicted because genetic background and environment also play a role. It describes genetic counseling as mandatory so couples understand that risk (Krausz et al., Andrology, 2014). A 2018 review states that the deletions are transmitted to 100% of male offspring born through assisted reproduction (Colaco and Modi, Reproductive Biology and Endocrinology, 2018).
The AUA guideline adds a practical point. When sperm are obtained, men should be counseled about the risk that sons will inherit an AZFc deletion and be infertile, and about preimplantation genetic testing with assisted reproduction, because some couples may choose to transfer only female embryos to avoid a son with congenital infertility (Brannigan et al., Journal of Urology, 2024). That is a personal decision with ethical weight, and it is exactly the kind of conversation a genetic counselor is there to hold. The 2013 European guideline also notes that in rare cases an AZFc deletion in a man with some sperm can be passed on without assisted reproduction (Krausz et al., Andrology, 2014).
Who Should Be Tested for a Y-Chromosome Microdeletion?
The AUA and American Society for Reproductive Medicine (ASRM) guideline recommends Y-chromosome microdeletion analysis for men with primary infertility (never having fathered a child) and azoospermia or a sperm concentration of 1 million per mL or lower, when that comes with a raised FSH, testicular atrophy, or a diagnosis of impaired sperm production. It grades this a moderate recommendation backed by grade B evidence (Brannigan et al., Journal of Urology, 2024). FSH is the pituitary hormone that tells the testes to support sperm production, and it often rises when the testes are struggling; our FSH article explains how to read it. Testicular atrophy means smaller or shrunken testes.
The 2024 amendment lowered the sperm-count cutoff for this test. The earlier AUA threshold was 5 million per mL. A 2019 meta-analysis of 37 studies (12,492 oligozoospermic men in Europe and North America) pooled 18 of them (10,866 men) and found complete deletions in 5.0% of men with concentrations above 0 to 1 million per mL, but only 0.8% of men at above 1 to 5 million per mL and 0.5% at above 5 to 20 million per mL (Kohn et al., European Urology, 2019). Karyotype testing, which looks for whole-chromosome problems, stays recommended under the same guideline for men with azoospermia or a concentration below 5 million per mL who also have those warning signs.
The European guideline adds that men with azoospermia who might be candidates for TESE and ICSI should be offered the test, because TESE is not recommended when the AZFa region is completely deleted (Krausz et al., Andrology, 2014). Testing is done on a blood sample, and it is ordered by a physician, not something to buy as a stand-alone online panel.
What We Are More Skeptical About
We are skeptical of any single retrieval figure. The 47% mean for AZFc deletions hides a range from 13% to 100% across 32 studies, many of them small, and rates depend heavily on the surgeon and the center (Yuen et al., Translational Andrology and Urology, 2021). Your own odds are not the average.
We are also cautious about two kinds of certainty. The first is the idea that a complete AZFb deletion always means zero sperm. Two men in a 2017 case report had an AZFb deletion on the first-line test and still had some residual sperm production, and extra testing revealed an unusual deletion pattern that the basic test had not captured (Stouffs et al., Andrology, 2017). Two men is not a trend, but it shows why the exact boundaries of a deletion need to be read carefully before anyone is told that no treatment is possible. The AUA makes the same point about partial deletions, which are harder to interpret because there is no standardized clinical test for them, and notes that a small partial AZFa deletion has been reported with no effect on sperm production (Brannigan et al., Journal of Urology, 2024). The 2023 European guideline recommends a basic multiplex PCR test followed by a deletion extension analysis, and warns that many commercial kits test an unnecessarily high number of markers (Krausz et al., Andrology, 2024).
The second is the testing cutoff. The AUA moved to 1 million per mL on the strength of the 2019 meta-analysis, but the topic is not closed: a published letter in response argued that the indication for testing should not rest on sperm concentration alone (Ferlin, European Urology, 2020). We also hold the 2024 IVF numbers lightly. They compare men with deletions against other infertile men in observational studies, which cannot fully separate the effect of the deletion from other differences between the groups, and the authors call for more work to understand why embryo outcomes might be affected (Colaco and Modi, Fertility and Sterility, 2024).
Finally, we are not aware of any evidence that supplements or lifestyle changes bring back sperm production that has been lost because a region of the Y chromosome is missing. Healthy habits still matter for general health, but they do not replace the deleted genes. And every number above measures sperm, retrieval, or IVF outcomes. None of it tells any one couple whether they will have a baby, which also depends on the female partner's age and fertility.
How Should You Think About This Practically?
Start by confirming the basics. A semen analysis showing no sperm or a very low count should be repeated, and it should be read alongside a hormone panel (FSH, LH, and testosterone) and a physical exam, because the first job is separating a blockage from a production problem. If the pattern points to a production problem, ask your urologist about a karyotype and a Y-chromosome microdeletion test, and ask which region the report names. A report that names an AZFc deletion and one that names an AZFa deletion lead to very different conversations.
If a deletion is confirmed, ask for a referral to a urologist or andrologist who performs micro-TESE regularly, since surgeon experience is one of the few factors a couple can actually choose. Ask for genetic counseling before any procedure, and bring your partner into the conversation early, because decisions about ICSI, embryo testing, and what to tell a future son are made together.
If you are a clinician, a hormone panel and semen analysis together are the starting point for flagging which patients should go on to genetic testing, and for tracking results over time.
Our Take
We know that Y-chromosome microdeletions are a recognized genetic cause of no sperm or very low sperm counts, that the missing region decides the odds, and that complete AZFa and AZFb deletions have not produced retrievable sperm in the published series. We know AZFc deletions often still leave sperm that surgery can find in roughly half of attempts, and that a son conceived this way is expected to inherit the deletion.
What we do not know is how to predict an individual man's retrieval odds, how much an AZFc deletion changes IVF outcomes once study design is accounted for, and exactly where the testing cutoff should sit. We still think it is worth acting on early. A clear answer about which region is involved can save a man from an operation that cannot work, or open the door to one that can. Know your numbers, get the right genetic test when the pattern fits, and see someone who does this surgery often.
SwimScore does not test for Y-chromosome microdeletions, which need a physician-ordered DNA test. SwimScore Complete measures sperm concentration, progressive motility, total motility, morphology, DNA Fragmentation Index (DFI), and a hormone panel including FSH, LH, and testosterone from a home sample. A count at or near zero, especially alongside a high FSH, is a clear reason to take your results to a urologist and ask about genetic testing.
FAQ
What is a Y-chromosome microdeletion?
A Y-chromosome microdeletion is a small missing piece of the Y chromosome, in a region (AZF) that holds genes needed to make sperm. The AUA estimates it is present in 8% to 12% of men with non-obstructive azoospermia and 3% to 7% of men with severe oligospermia (Brannigan et al., Journal of Urology, 2024).
Can a man with a Y-chromosome microdeletion have a biological child?
Sometimes. In a Weill Cornell series, sperm were found in 56% of men with an isolated AZFc deletion, but in none of the men with complete AZFa or AZFb deletions (Hopps et al., Human Reproduction, 2003). Any sperm found are used with ICSI.
What is the difference between AZFa, AZFb, and AZFc deletions?
They are three regions on the long arm of the Y chromosome. Complete AZFa or AZFb deletions are associated with no retrievable sperm, while AZFc deletions often leave some sperm production, with a mean micro-TESE retrieval rate of 47% across 32 studies (Yuen et al., Translational Andrology and Urology, 2021).
Will my son inherit a Y-chromosome microdeletion?
A son conceived with the father's sperm through assisted reproduction is expected to inherit the deletion, and the European guideline calls genetic counseling mandatory (Krausz et al., Andrology, 2014). The exact effect on his fertility cannot be predicted.
Who should get a Y-chromosome microdeletion test?
The AUA and ASRM guideline recommends it for men with primary infertility and azoospermia or a sperm concentration of 1 million per mL or lower, when accompanied by a raised FSH, testicular atrophy, or impaired sperm production (Brannigan et al., Journal of Urology, 2024).
References
- Brannigan RE, et al. Updates to Male Infertility: AUA/ASRM Guideline (2024). Journal of Urology. 2024. https://pubmed.ncbi.nlm.nih.gov/39145501/
- Krausz C, Hoefsloot L, Simoni M, Tüttelmann F. EAA/EMQN best practice guidelines for molecular diagnosis of Y-chromosomal microdeletions: state-of-the-art 2013. Andrology. 2014. https://pubmed.ncbi.nlm.nih.gov/24357628/
- Krausz C, Navarro-Costa P, Wilke M, Tüttelmann F. EAA/EMQN best practice guidelines for molecular diagnosis of Y-chromosomal microdeletions: State of the art 2023. Andrology. 2024. https://pubmed.ncbi.nlm.nih.gov/37674303/
- Hopps CV, et al. Detection of sperm in men with Y chromosome microdeletions of the AZFa, AZFb and AZFc regions. Human Reproduction. 2003. https://pubmed.ncbi.nlm.nih.gov/12871878/
- Yuen W, Golin AP, Flannigan R, Schlegel PN. Histology and sperm retrieval among men with Y chromosome microdeletions. Translational Andrology and Urology. 2021. https://pubmed.ncbi.nlm.nih.gov/33850779/
- Colaco S, Modi D. Azoospermia factor c microdeletions and outcomes of assisted reproductive technology: a systematic review and meta-analysis. Fertility and Sterility. 2024. https://pubmed.ncbi.nlm.nih.gov/37923163/
- Colaco S, Modi D. Genetics of the human Y chromosome and its association with male infertility. Reproductive Biology and Endocrinology. 2018. https://pubmed.ncbi.nlm.nih.gov/29454353/
- Kohn TP, Kohn JR, Owen RC, Coward RM. The Prevalence of Y-chromosome Microdeletions in Oligozoospermic Men: A Systematic Review and Meta-analysis of European and North American Studies. European Urology. 2019. https://pubmed.ncbi.nlm.nih.gov/31400948/
- Stouffs K, Vloeberghs V, Gheldof A, Tournaye H, Seneca S. Are AZFb deletions always incompatible with sperm production? Andrology. 2017. https://pubmed.ncbi.nlm.nih.gov/28395120/
- Ferlin A. Re: Kohn et al., The Prevalence of Y-chromosome Microdeletions in Oligozoospermic Men. Indication for Y Chromosome Microdeletion Analysis in Infertile Men Should Not be Based Merely on Sperm Concentration. European Urology. 2020. https://pubmed.ncbi.nlm.nih.gov/31980313/
Fertility clinics and urology practices: if a patient's semen analysis shows no sperm or a very low count alongside a raised FSH, see how SwimScore can support your workflow on our clinic page.
This article is for general education and is not medical advice. A suspected Y-chromosome microdeletion, and any decision about genetic testing, sperm retrieval, or embryo testing, should be reviewed with a physician and a genetic counselor who know your full history.
SwimScore uses CLIA-certified labs for all semen analysis and hormone testing, assessed against WHO 6th Edition clinical thresholds.
