Male infertility can involve sperm production, sperm delivery, hormones, ejaculation or several factors together. A structured assessment can identify causes that need treatment.
Male fertility can be reduced by problems with sperm production, sperm movement, the route sperm take out of the body, hormonal signalling, erections or ejaculation. Medical treatment, genetic conditions and some exposures can also contribute. In many cases there is more than one factor, and sometimes no single cause is found.
A risk factor is not the same as a diagnosis. Smoking, obesity and excessive alcohol intake are associated with poorer fertility or semen quality at a population level, but they do not explain every abnormal result. The cause should be assessed from the history, examination, semen analyses and selected further tests.
The testicles produce sperm through a process controlled by hormones from the brain and pituitary gland. A problem in the testicles, hormonal signalling or sperm-development process can lead to:
These laboratory descriptions do not identify why the result is abnormal. A repeat semen analysis and clinical assessment are normally needed before the pattern is attributed to a disease or used to select treatment.
Sperm production may be affected by a condition present from birth or acquired later. Relevant examples include:
These histories justify earlier fertility assessment. NICE recommends referral at presentation when either partner has a known or suspected cause or a predisposing history; there is no requirement to try for a year first.
Sperm may be produced but prevented from entering the semen. This is called obstructive azoospermia when no sperm appear in the ejaculate because of a blockage or absent duct.
Potential causes include:
Semen volume, examination findings and hormone results can help distinguish an obstruction from reduced sperm production. Ultrasound or genetic testing is used when clinically indicated rather than for every abnormal count.
The hypothalamus and pituitary gland signal the testicles through luteinising hormone and follicle-stimulating hormone. Disruption at any level may reduce sperm production.
Possible causes include hypogonadotropic hypogonadism, pituitary disease, raised prolactin and primary testicular failure. Symptoms such as reduced sexual desire or changes in secondary sexual characteristics may provide clues, but some men have few symptoms.
A single testosterone result is not enough to define the cause. A clinician may assess morning testosterone alongside gonadotrophins and other tests chosen from the history. Testosterone prescribed from outside the body is different from testosterone produced within the testicle: replacement testosterone can suppress the pituitary signals required for sperm production and is not a treatment for male infertility.
A varicocele is an enlargement of veins around the testicle. It is common, and many men with a varicocele are fertile. A clinically detectable varicocele can, however, be associated with reduced semen parameters in some men.
Current NICE guidance says radiological or surgical treatment may be considered when the varicocele is found on clinical examination, the couple is trying to conceive spontaneously and semen parameters are reduced. The partner's fertility and the couple's timeframe should also be taken into account. Treating an incidental or ultrasound-only finding is not automatically beneficial.
Sperm production can be normal while delivery is impaired. Fertility may be affected by:
The cause determines the least invasive option. Assessment may include a sexual and medication history and, when retrograde ejaculation is suspected, testing urine after orgasm for sperm.
Genetic investigation is targeted to clinical findings and the severity of the semen abnormality. Under NICE guideline NG257:
The purpose is not only to explain the result. Some findings alter the probability of retrieving sperm or indicate a chance of passing a condition to a child.
NICE advises clinicians to ask specifically about prescription medicines, over-the-counter products and recreational drugs. Examples named in the guideline include testosterone-replacement therapy, finasteride, GLP-1 receptor agonists, non-steroidal anti-inflammatory drugs, anabolic steroids and cannabis. Inclusion on that list does not mean every product causes infertility in every user; it means the potential effect and the reason for treatment should be reviewed.
Other histories with a recognised fertility risk include chemotherapy, pelvic radiotherapy and some surgery. Sperm freezing should be discussed as early as possible before a medical treatment likely to cause infertility.
Never stop prescribed medicine without the clinician who manages it. For some conditions, stopping abruptly presents a greater health risk, and a suitable alternative may require planning.
Lifestyle changes cannot correct every cause, but several factors warrant discussion:
| Area | Examples | Assessment may include |
|---|---|---|
| Sperm production | Previous undescended testicle, torsion, orchitis, cancer treatment or genetic condition | Repeat semen analysis, examination, hormones and selected genetic tests |
| Sperm transport | Vasectomy, congenital absence of the vas deferens or acquired blockage | Examination, semen features, imaging and CFTR testing when indicated |
| Hormonal signalling | Pituitary disorder, hypogonadotropic hypogonadism or testicular failure | Symptoms, examination, testosterone, gonadotrophins and targeted tests |
| Sexual function and ejaculation | Erectile dysfunction, anejaculation or retrograde ejaculation | Sexual and medication history, examination and selected urine testing |
| Lifestyle or exposure | Smoking, excessive alcohol, obesity, anabolic steroids or occupational hazards | Specific exposure review rather than assuming it is the sole cause |
Semen analysis measures selected features, and current tests cannot explain every defect in sperm production or function. “Idiopathic male infertility” describes an abnormal fertility assessment without an identified cause. “Unexplained infertility” generally means that standard investigations have not identified a cause in either partner.
An unexplained result should not prompt indiscriminate testing or supplements. NICE advises against sperm DNA-fragmentation testing in the standard UK pathway and against supplements or antioxidants intended to improve sperm DNA integrity. A specialist can explain whether any additional test is likely to change management.
