Fertility problems are experienced by a large number of couples who are trying to conceive - around 3.5 million people in the UK. So let’s take a quick look at the most widespread causes of infertility for both women and men.

Problems with ovulation

Infertility in women is most commonly caused by problems with ovulation (the monthly release of an egg). While some problems prevent an egg from being released at all, others stop it being released during some cycles only. This can be caused by:

  • Polycystic Ovary Syndrome (PCOS) – small cysts around the ovaries can affect hormone production and fertility.
  • Thyroid problems
  • Premature ovarian failure

Low sperm count

A very low sperm count (also called oligozoospermia) or no sperm at all is a common cause of infertility. A low sperm count is classified as fewer than 15 million sperm per millilitre of semen.

Poor sperm health

Poor sperm health includes movement and shape. If the sperm has poor movement, it’s harder for it to swim to reach the egg. Sometimes sperm can be abnormally shaped; again this stops it moving as easily to fertilise an egg.

Blocked fallopian tubes

There are a number of causes of blocked fallopian tubes – these include:

  • Infection, often caused by chlamydia
  • Scarring from abdominal surgery
  • Inflammation caused by appendicitis.
  • Severe endometriosis
  • Large fibroids in the uterus
  • Sterilisation

Poor Egg Health

The biggest factor in egg health is age: unfortunately, older women are more likely to produce less healthy eggs. But poor diet and poor lifestyle habits can also affect egg quality, so a healthy lifestyle and diet can be beneficial.


Anti-sperm antibodies (ASA)

These are antibodies that fight against a man's sperm, stopping fertilisation. There are three ways this happens:

  • The sperm can clump together, reducing the number that can make their way through cervical mucus
  • The sperm can be immobilised, leaving it unable to move
  • The sperm can become spermatotoxic, meaning they’re no longer viable

Anti-sperm antibodies can also sometimes be found in women.

Vas deferens blockage

If the vas deferens – the small tubes that carry sperm to the urethra for ejaculation – are blocked, sperm can’t mix with a man's semen. If the semen contains no sperm, it can’t fertilise an egg. 

Combination infertility

Around 40% of cases of infertility are caused by combination infertility. This is where a couple has both male and female infertility problems, or when one of them has more than one fertility problem.

Unexplained infertility

For 25% of couples, the cause of infertility can’t be found – this is known as unexplained infertility. You can find out more about unexplained infertility here.

Now that you’ve got a better idea of the most common causes of infertility, if you’re trying to get pregnant you might want to read our blog post 5 Reasons Why You Might Not be Getting Pregnant. And if you need some extra help working out when you’re at your most fertile, why not try our ovulation calculator to help you keep track?

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Mr Andrew Drakeley Andrew Drakeley

Mr Andrew Drakeley is the Clinical Director at the Hewitt Fertility Centre, working principally at the Liverpool Women’s site but with managerial responsibility for Knutsford.

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