Male fertility: how often it is a factor and the first test

Infertility is usually defined as no pregnancy after 12 months of regular sex without contraception, or after 6 months when the woman is 35 or older (StatPearls, Female Infertility, 2026). Male fertility is a cause, or one of the causes, in a large share of those couples. This page sets out how large a share, what the main causes are, and how a man's fertility is assessed.

A male factor contributes to between 40 and 50 in 100 cases of infertility

Published estimates vary with the source. The StatPearls review of male infertility (2026) states that a male factor contributes to about 50% of infertility cases, and its companion review of female infertility (2026) gives about 40%. Many of these couples also have a female factor, which is why both reviews recommend assessing the two partners together.

A male factor on its own is less common, and harder to count. Estimates of infertility with a purely male cause, collected by Agarwal and colleagues and cited in StatPearls (2026), range from 2.5% to 12% depending on the region studied.

Most male infertility begins in the testes

StatPearls (2026) groups the causes of male infertility into four broad categories, with an estimated share for each:

• Primary testicular defects, about 65% to 80% of cases. This group includes abnormal sperm counts, movement or shape for which no cause is found.
• Idiopathic infertility, about 10% to 20%, in which the semen and sperm results are normal but the man remains infertile.
• Sperm transport disorders, about 5%, such as a blockage or a vasectomy.
• Endocrine disorders, about 2% to 5%, usually hypogonadism, an abnormally low level of testosterone.

The review describes these shares as broad estimates, because infertility is under-reported and most recorded cases come from specialist referral centers. The World Health Organization's list of causes is similar: blockages in the tubes that carry semen, hormonal disorders, failure of the testes to produce sperm, and abnormal sperm shape or movement (WHO, Infertility fact sheet, 2025).

A varicocele, an enlarged vein in the scrotum, is the most common cause of male infertility that can be corrected. Varicoceles are found in about 15% of men, and in about 40% of men with an abnormal semen analysis (StatPearls, "Male Infertility", 2026).

Testosterone therapy and anabolic steroids lower sperm production

Testosterone taken as a medicine lowers the pituitary hormones that drive sperm production. StatPearls (2026) states that testosterone therapy suppresses sperm production even when it is prescribed correctly for a confirmed condition, and that production recovers in most men after stopping, although recovery can take up to two years. The WHO fact sheet (2025) lists anabolic steroid use among the causes of abnormal semen results. For anyone taking testosterone on prescription, this is a question to raise with the prescriber before trying to conceive, rather than a reason to stop the medicine unaided.

A semen analysis is the first test of male fertility

An assessment usually begins with a medical and sexual history, a physical examination and a semen analysis, which measures the volume of semen and the number, movement and shape of the sperm (StatPearls, "Male Infertility", 2026; MedlinePlus, 2025). Because results vary from one sample to the next, an abnormal first result is repeated before any conclusion is drawn. Further tests, such as hormone levels, genetic tests or an ultrasound scan of the testes, depend on what the semen analysis shows (StatPearls, "Male Infertility", 2026; NHS, Low sperm count, 2024). What a result below the reference limits means is explained in the guides to a low sperm count and to azoospermia, when no sperm are found.

US and UK guidance set slightly different points for an assessment

• US: an infertility evaluation is usually offered after 12 months of trying, or after 6 months when the woman is 35 or older (StatPearls, Female Infertility, 2026).
• UK: the NHS advises seeing a GP after more than a year of trying, or after 6 months if the partner is 36 or older (NHS, Low sperm count, 2024).

The NHS also advises speaking to a GP before trying to conceive if either partner has a known fertility issue, such as a low sperm count, or has had treatment for cancer (NHS, Planning your pregnancy, 2026).

Lifestyle factors have smaller and better-defined effects

Smoking, obesity, heavy drinking and anabolic steroids are all linked to poorer semen results, with evidence of different strength for each. The guide to sperm health sets out what the studies found, factor by factor, and the guide to the preconception checkup covers what both partners can review with a doctor before trying.