What affects your fertility?

sperm surrounding egg illustration A man releases millions of sperm during sex, but just one can fertilise a woman's egg

Infertility is when a couple cannot conceive despite having regular unprotected sex. It can be caused by a range of disorders and lifestyle factors. However, fertility problems cannot be explained in around a third of cases.

What causes infertility in women?

Fertility facts

  • For couples who have been trying to conceive for more than three years , the likelihood of pregnancy occurring within the next year is 25% or less
  • Around one in six couples can have difficulty conceiving. This is approximately 3.5 million people in the UK
  • About 85% of couples will conceive naturally within a year if they have regular unprotected sex but the chance of becoming pregnant is much lower for women over 36

Source: NHS Choices

The hormones oestrogen and progesterone control a woman's monthly fertility cycle.

An egg is released each month as these hormone levels change. The egg then travels into the fallopian tubes which connect the ovaries to the womb, or uterus. This process is called ovulation.

In women, infertility is due to problems with ovulation in about one in three cases. Some issues prevent women from releasing any eggs, in other cases an egg is only released on some monthly cycles.

Ovulation problems can occur as a result of a number of conditions, such as polycystic ovary syndrome, thyroid problems or premature ovarian failure, which is when a woman's ovaries stop working before the age of 40.

However, many other conditions can cause a woman to have problems with fertility. It may be difficult to become pregnant, for example, if the womb or fallopian tubes are damaged.

Another common cause of infertility is when small pieces of the womb lining are found outside the womb. This is called endometriosis and it affects around two million women in the UK.

What causes infertility in men?

Male infertility is caused by abnormal semen (the fluid containing sperm that is released during sex). Issues include:

  • A low sperm count or no sperm at all
  • Decreased sperm mobility - making it harder for the sperm to reach the egg
  • Sperm with an abnormal shape, which makes it harder for them to move

Damage to a man's testicles can also affect the quality of sperm. Damage can occur due to a range of problems including:

Other causes of infertility or reduced fertility

Age - Both men and women are their most fertile in their early 20s. Female fertility declines sharply after the age of 35. Around one in three of couples in which the woman is over 35 have fertility problems. This rises to two-thirds when the woman is over 40. Male fertility gradually declines from the age of 40.

Hormonal disorders - An underactive thyroid or a malfunctioning pituitary gland can cause fertility issues.

Smoking - Studies have shown that women who smoke take longer to conceive. Research has found that the toxic chemicals in cigarettes can damage the lining of the fallopian tubes, which help transport the egg from the ovary to the womb. Partners of men who smoke also have a reduced chance of conceiving as smoking can decrease the amount of sperm produced and their motility.

Drinking - alcohol can reduce fertility in both men and women. It is not yet understood exactly how alcohol affects fertility but studies have shown drinking alcohol reduces the chances of a woman conceiving. In men, heavy drinking may affect sperm quality which can impact on chances of a successful pregnancy.

Ways to boost fertility

  • Having sex every two or three days gives the best chance of conceiving. Doctors say you don't need to aim for an 'ovulation window' (the time in a woman's cycle when she's most likely to ovulate).
  • Avoid smoking. This can damage a man's sperm, and women who smoke take longer to conceive.
  • Testicles should be one or two degrees cooler than the rest of a man's body, so avoid tight underwear or clothes.
  • Be a healthy weight. Being under or overweight can lower conception chances.
  • Keep as healthy as possible and deal with stress.

Source: NHS Choices

Bad timing - an egg is fertilised when a man's sperm meets the woman's egg at about the time of ovulation, which is when the egg is released from the ovaries. Women mostly ovulate once during each cycle, and the most likely time for conception is 14 days before a period.

Stress - Worry and tension can cause hormonal changes in the body, which can lead to fertility problems.

Sexually Transmitted Infections - Chlamydia can cause pelvic inflammatory disease (PID) as well as fallopian tube infection in women. Both may cause permanent damage to the fallopian tubes and uterus, leading to infertility. Gonorrhoea can also cause PID and reduce fertility in men as well.

Unhealthy body weight - If you're very underweight it can be more difficult to conceive. Being obese may also cause problems with conceiving.

For information on symptoms and treatments, please visit NHS Choices

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