The causes of infertility

If you are having difficulty becoming pregnant, you are not alone. Around one in six to one in seven couples have trouble conceiving naturally.


Infertility is when a couple cannot conceive despite having regular unprotected sex for at least a year.

The cause varies from person to person and couple to couple. It can be related to male or female factors, or both.

The only way to really understand what is happening with your fertility is to have a fully comprehensive fertility test. For men, this is a semen analysis to assess your sperm quality. For women, blood tests and ultrasound scans to look at your fertility hormone levels, estimate how many eggs you are likely to have, check whether you are ovulating normally and make sure there are no visible abnormalities in your ovaries and uterus. 

London Fertility Centre offers some of the most comprehensive fertility testing packages in the UK for women, men and couples.

Common causes of infertility

  • Lifestyle factors play a very important role in both male and female fertility. Being underweight or overweight, drinking too much alcohol, smoking and having a low level of fitness can all seriously impact your ability to conceive
  • Stress can have a major impact on your sex drive and the frequency of intercourse
  • Sexually transmitted diseases can cause problems. For example, chlamydia in women can result in scarring and blockage of the fallopian tubes
  • Chemotherapy and radiotherapy can affect your fertility. If you want to have children in the future and are about to have a course of chemotherapy or radiotherapy you may want to consider freezing your sperm, eggs or embryos before treatment
  • Drugs, including marijuana and cocaine, may have an effect on sperm and egg production and quality


  • Age affects the quality of your eggs and the regularity with which they are released. After 35, you are likely to be half as fertile as you were at 25
  • Premature ovarian aging (POA) is when you have an even more rapid decline in your fertility. It is more common than many people realise, with around nine per cent of women affected
  • Premature ovarian failure (POF), also known as premature menopause, is when your ovaries stop working completely before the age of 40. It affects one per cent of women
  • Blockages or infection of your fallopian tubes can prevent sperm reaching your eggs
  • Fibroids are benign tumours of the womb. They can sometimes prevent your embryos from implanting, or cause miscarriage
  • Pelvic or cervical surgery can cause scarring, which may make it difficult for your mature eggs to travel down your fallopian tubes
  • If the mucus produced by the neck of your womb is too thick or there is too much of it, it will be difficult for sperm to swim through and get to the fallopian tubes to fertilise the egg
  • Long term or heavy use of non-steroidal anti-inflammatory medication, like asprin or ibuprofen, or use of anti-psychotic medication can make it more difficult for you to conceive
  • Polycystic ovary syndrome and thyroid problems can affect how often you release eggs to be fertilised


  • Problems with the quality of semen are a common cause of infertility. You may find you have a low sperm count, slow moving sperm or abnormally shaped sperm. This could be caused by a genetic condition, certain medications or lifestyle factors like smoking, alcohol, drug use, obesity or low fitness levels, however in many cases the cause may not be able to be identified
  • Problems with your testicles can make it difficult to conceive. This may include injury, infection, scarring from surgery, a naturally occurring defect or undescended testicles
  • You may have a blockage in your vas deferens – the ducts that carry sperm from the testes to the urethra. This can stop sperm appearing in your ejaculate
  • Premature ejaculation or retrograde ejaculation, where semen is ejaculated into your bladder, can prevent you from inseminating your partner’s eggs