What causes male infertility, and how is it checked?

Male factor is common, and it is no one's fault

When a couple finds it hard to conceive, the reason can lie with either partner, with both, or with neither that tests can find. Male factors are found in a large share of couples, sometimes on their own and often alongside a female factor. That is why a fertility evaluation looks at both partners from the start.

Sperm quality says nothing about how "manly" someone is, or about their sex life. Most men with a sperm problem feel completely well and have no symptoms at all.

How sperm are made and delivered

It helps to know the basic steps. Sperm are made in the testes, under the control of hormones from the pituitary gland in the brain. They mature in a coiled tube behind each testis (the epididymis), travel up a tube called the vas deferens, mix with fluid from other glands, and leave the body during ejaculation.

A problem at any of these steps can affect fertility.

The main groups of causes

Group	What happens	Some examples
Sperm production	The testes make fewer sperm, or sperm that move or are shaped less typically	Undescended testes in childhood, injury, mumps after puberty, genetic conditions
Blockage	Sperm are made but cannot get out	Past infection, previous surgery or vasectomy, a tube missing from birth
Ejaculation and erection	Sperm do not reach the vagina	Erection difficulties, ejaculation that goes backwards into the bladder (retrograde ejaculation), spinal injury
Hormones	The brain sends too little signal to the testes	Low pituitary hormones, high prolactin, thyroid problems
Varicocele	Enlarged veins in the scrotum, a bit like varicose veins	Often found on examination; many men with one are fertile
Genes	Differences in chromosomes or genes affect sperm production or the tubes	Klinefelter syndrome, small missing pieces of the Y chromosome, cystic fibrosis gene changes
Medicines and drugs	Some substances switch off or slow sperm production	Testosterone, anabolic steroids, some prescription medicines
Past cancer treatment	Chemotherapy or radiotherapy can damage sperm-making cells	Effects may be temporary or lasting

A few points worth knowing

• Infections. Sexually transmitted infections such as chlamydia and gonorrhoea, and tuberculosis affecting the genital tract, can scar the tubes. Mumps that affects the testes after puberty can reduce sperm production.
• Varicocele. Whether treating a varicocele improves the chance of pregnancy is debated, and guidelines differ. A specialist can explain whether it is relevant in your situation.
• Diabetes can affect erections and ejaculation, and some medicines for blood pressure, mood or the prostate can affect ejaculation.

Caution. Testosterone injections, gels and "boosters", and anabolic steroids used for bodybuilding, tell the brain to stop signalling the testes. This can lower sperm count sharply, sometimes to zero. If you are trying to conceive, don't start testosterone without discussing fertility with a doctor, and don't stop any prescribed medicine without advice.

Often, no clear cause is found

In many men with an unusual semen analysis, tests do not find a single reason. This is sometimes called unexplained or idiopathic male infertility. It can feel frustrating, but treatment decisions can still be made based on the results themselves.

How a male partner is usually evaluated

1. History. A doctor asks about childhood conditions such as undescended testes, past infections or surgery, medicines, supplements, work, smoking, alcohol and sexual function.
2. Semen analysis. Usually the first test. If it is unusual, it is repeated, as results vary from one sample to the next.
3. Physical examination. Checking the size and feel of the testes, the tubes, and for a varicocele.
4. Blood tests. Hormones such as FSH, LH, testosterone and sometimes prolactin, when the count is low or the history suggests it.
5. Further tests when needed. A scrotal ultrasound, a urine test after ejaculation (to look for retrograde ejaculation), or genetic tests when the count is very low or no sperm are seen.

Who does what

A gynaecologist often coordinates a couple's evaluation and can arrange the first semen analysis and blood tests. A urologist or andrologist (a doctor who specialises in male reproductive health) is the right person for a physical examination of the testes, for treating blockages, varicocele or ejaculation problems, and for surgical sperm retrieval. Our specialist checker can help you work out who to see.

When to see a doctor

• If you have been trying for a year (or six months if the female partner is 35 or older), both partners should be checked.
• See a doctor sooner if you have had undescended testes, surgery on the testes or groin, mumps after puberty, cancer treatment, or difficulty with erections or ejaculation.
• See a doctor promptly for a lump, swelling or ache in a testis.
• Sudden, severe pain in a testis is an emergency (it can mean the testis has twisted). Call 112 or go to the nearest hospital straight away.