Infertility can be caused by many different things. For 25% of couples, a cause cannot be identified.
Infertility in women
Infertility is most commonly caused by problems with ovulation (the monthly release of an egg). Some problems stop women releasing eggs at all, and some cause an egg to be released during some cycles, but not others.
Ovulation problems can occur as a result of a number of conditions, listed below.
- Polycystic ovary syndrome (PCOS), a condition that makes it more difficult for your ovaries to produce an egg.
- Thyroid problems, both an overactive thyroid gland (hyperthyroidism) and an underactive thyroid gland (hypothyroidism) can prevent ovulation.
- Premature ovarian failure, where a woman’s ovaries stop working before she is 40.
Womb and fallopian tubes
The fallopian tubes are the tubes along which an egg travels from the ovary to the womb. The egg is fertilised as it travels down the fallopian tubes. When it reaches the womb, it is implanted into the womb's lining where it continues to grow.
If the womb or the fallopian tubes are damaged, or stop working, it may be difficult to conceive naturally. This can occur following a number of factors, outlined below.
Scarring from surgery
Pelvic surgery can sometimes cause damage and scarring to the fallopian tubes.
Cervical surgery can also sometimes cause scarring, or shorten the cervix (the neck of the womb).
Cervical mucus defect
When you are ovulating, mucus in your cervix becomes thinner so that sperm can swim through it more easily. If there is a problem with your mucus, it can make it harder to conceive.
Fibroids are benign (non-cancerous) tumours that grow in, or around, the womb. Submucosal fibroids develop in the muscle beneath the inner lining of the womb wall and grow into the middle of the womb.
Submucosal fibroids can reduce fertility, although exactly how they do this is not yet known. It is possible that a fibroid may prevent an embryo from implanting itself into your womb.
Endometriosis is a condition where small pieces of the womb lining, known as the endometrium, start growing in other places, such as the ovaries.
This can cause infertility because the new growths form adhesions (sticky areas of tissue) or cysts (fluid-filled sacs) that can block or distort the pelvis. These make it difficult for an egg to be released and become implanted into the womb.
It can disturb the way that a follicle (fluid-filled space in which an egg develops) matures and releases an egg.
Pelvic inflammatory disease
Pelvic inflammatory disease (PID) is an infection of the upper female genital tract, which includes the womb, fallopian tubes and ovaries. It is often the result of a sexually transmitted infection (STI). PID can damage and scar the fallopian tubes, making it virtually impossible for an egg to travel down into the womb.
Some women choose to be sterilised if they do not wish to have any more children.
Sterilisation involves blocking the fallopian tubes to make it impossible for an egg to travel to the womb. This process is rarely reversible, and if you do have a sterilisation reversed, it will not necessarily mean that you will become fertile again.
Medicines and drugs
The side effects of some types of medication and drugs can affect your fertility. These medicines are outlined below.
- Non-steroidal anti-inflammatory drugs (NSAIDs). Long-term use or a high dosage of NSAIDs, such as ibuprofen or aspirin, can make it more difficult for you to conceive.
- Chemotherapy – Medicines used for chemotherapy (a treatment for cancer) can sometimes cause ovarian failure, which means your ovaries will no longer be able to function properly. Ovarian failure can be permanent.
- Neuroleptic medicines are antipsychotic medicines often used to treat psychosis. They can sometimes cause missed periods or infertility.
- Spironolactone - this is a type of medicine used to treat fluid retention (oedema). Fertility should recover around two months after you stop taking spironolactone.
Illegal drugs such as marijuana and cocaine can seriously affect fertility, making ovulation (the monthly cycle where an egg is released from the ovaries) more difficult.
Infertility in women is also linked to age. The biggest decrease in fertility begins during the mid-thirties. Among women who are 35, 95% will get pregnant after three years of having regular unprotected sex. For women who are 38, only 75% will get pregnant after three years of having regular unprotected sex.
Infertility in men
Male infertility is caused by abnormal semen (the fluid containing sperm that is ejaculated during sex). Some possible reasons for abnormal semen are listed below.
- Decreased number of sperm – You may have a very low sperm count, or no sperm at all.
- Decreased sperm mobility – If you have decreased sperm mobility, it will be harder for your sperm to swim to the egg.
- Abnormal sperm – Sometimes sperm can be an abnormal shape, making it harder for them to move and fertilise an egg.
- Many cases of abnormal semen are unexplained, but there are several factors that can affect semen and sperm.
The testicles are responsible for producing and storing sperm. If they are damaged it can seriously affect the quality of your semen. This may occur if you have, or have had in the past, any of the following:
- an infection of your testicles
- testicular cancer
- testicular surgery
- a congenital defect (a problem with your testicles that you were born with)
- undescended testicles (when one or both of your testicles has not descended into the scrotum)
- trauma (injury) to your testicles
Absence of sperm
Your testicles may produce sperm, but it may not reach your semen. The absence of sperm in your semen is known as obstructive azoospermia. This could be due to a blockage in one of the tiny tubes that make up your reproductive system, which may have been caused by an infection or surgery.
A vasectomy is the surgical procedure for male sterilisation. It involves cutting and sealing off the vas deferens (the tubes that carry sperm out of your testicles), so that your semen will no longer contain any sperm. A vasectomy can be reversed, but reversals are not usually successful.
Some men experience ejaculation problems that can make it difficult for them to ejaculate. Other ejaculation problems include:
- retrograde ejaculation, where semen is ejaculated into your bladder
- premature ejaculation, where ejaculation occurs too quickly
Hypogonadism is an abnormally low level of testosterone, the male sex hormone that is involved in making sperm. This could be due to a tumour, taking illegal drugs, or Klinefelter's syndrome (a rare genetic condition where a man is born with an extra female chromosome).
Medicines and drugs
Certain types of medicines can sometimes cause infertility problems. These medicines are listed below.
- Sulfasalazine, an anti-inflammatory medicine used to treat conditions such as Crohn's disease (inflammation of the intestine) and rheumatoid arthritis (painful swelling of the joints). Sulfasalazine can decrease the number of sperm, but its effects are temporary and your sperm count should return to normal when you stop taking it.
- Anabolic steroids, often used illegally to build muscle and improve athletic performance. Long-term use or abuse of anabolic steroids can reduce sperm count and sperm mobility.
- Chemotherapy – Medicines used in chemotherapy can sometimes severely reduce sperm production.
- Herbal remedies – Some herbal remedies, such as root extracts of Tripterygium wilfordii (a Chinese herb), can affect the production of sperm or reduce the size of your testicles.
Illegal drugs such as marijuana and cocaine can also affect semen quality.
Drinking too much alcohol can damage the quality of your sperm. Guidelines published by the National Institute for Health and Care Excellence (NICE) state that if men follow the Department of Health’s recommendations of drinking no more than three to four units of alcohol a day, it is unlikely their fertility will be affected. However, drinking more than this could make it difficult to conceive.
Infertility in both men and women
There are a number of factors that can affect fertility in both men and women. These are outlined below.
Being overweight or obese reduces both male and female fertility. In women, being overweight can affect ovulation. Being underweight can also have an impact on fertility, particularly for women, who will not ovulate if they are severely underweight.
Sexually transmitted infections (STIs)
There are several STIs that can cause infertility. For example, chlamydia can damage the fallopian tubes in women, and cause swelling and tenderness of the scrotum (the pouch containing the testes) in men.
As well as affecting your general and long-term health, smoking can also adversely affect fertility. Read more information about quitting smoking.
Occupational and environmental factors
Exposure to certain pesticides, metals, and solvents can affect fertility in both men and women.
If either you or your partner are stressed, it may affect your relationship. Stress can contribute to a loss of libido (sex drive), which in turn can reduce the frequency of sexual intercourse. Severe stress may also affect female ovulation and limit sperm production.