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Fertility: how common is infertility and why does it happen?

The World Health Organization (WHO) defines infertility as the inability to conceive after 12 months or more of regular unprotected sexual intercourse.

Infertility can be classed as primary infertility, where individuals are unable to have a first child or secondary infertility where an individual previously had a live baby, but is unable to conceive again. Both primary and secondary infertility can be distressing.

If you have not conceived after one year of unprotected sex, you should be offered further investigations. You might be referred to a fertility clinic and offered counselling to help manage and process your feelings.


  • About 1 in 6 couples have difficulty in conceiving

  • Around 15% of adults are faced with infertility

Impact on mental health and relationships

Undergoing fertility investigations and treatments can prove to be very stressful. Statistics show that couples unable to have a baby can be up to three times more likely to separate or divorce.

If you feel that your fertility journey is impacting your mental health, you might want to access counselling to help you process your thoughts and feelings.

Causes of infertility


Your body needs to produce hormones and eggs normally to be fertile. Your fallopian tubes must be clear so that an egg can pass to the uterus, and your uterus needs to be capable of supporting a pregnancy. If any of these processes fail, you will have difficulty becoming pregnant.

Fertility problems in women are commonly caused by a failure to ovulate.This could be affected by ageing, smoking, polycystic ovary syndrome, early menopause, or hormonal issues.

Other causes of reduced fertility in women include obstructed fallopian tubes, endometriosis, and problems with the uterus, like fibroids or polyps.


For a man to be fertile, they must make and store an adequate amount of good quality sperm in the testicles and be able to ejaculate normally. If these processes are not functioning normally, his fertility will be affected.

The reason for a man’s infertility is often unknown.  Where an issue is identified, the most common cause is a problem with how the testicles work,  resulting in no sperm production, low sperm levels, or poor-quality sperm.

Sometimes all investigations and tests come back clear, and the cause of reduced fertility is not identified. This is called unexplained infertility.

What else can affect fertility?

Lifestyle factors

  • Alcohol- Excessive alcohol intake can reduce sperm quality in men.
  • Drug use- Some over the counter, prescribed, and recreational drugs can interfere with fertility for men and women.
  • Smoking- Smoking (including passive smoking) has been shown to reduce fertility for women and reduce sperm quality for men.
  • Stress- High levels of stress have been shown to impact fertility for men and women.

 Medical conditions or predisposition

  • Obesity- A Body Mass Index (BMI) of over 30 can reduce fertility for both men and women.
  • Low body weight- A BMI of less than 19 can affect menstruation, which may reduce the chances of conceiving.

Your doctor will explain about fertility investigations and possible treatment options, including in vitro fertilisation – also known as IVF.

Read about how infertility is investigated and next steps