Causes of Infertility

What are the main causes of female infertility? What are the main causes of female infertility?

What are the causes of infertility?

According to the National Institute for Health and Care Excellence (NICE), one in seven heterosexual couples in the UK is affected by infertility. Since their original guidelines were published in 2004, NICE has also reported an increase in the incidence of infertility, with more and more people seeking help and treatment. In Europe more widely, birth rate statistics have fallen for generations. While this in part is caused by a mix of social and cultural factors, it’s also due to infertility becoming increasingly common.

There can be many reasons why a couple may struggle to conceive. The most common causes of infertility are associated with male fertility factors as a result of poor sperm quality, accounting for roughly 30% of cases, while female fertility factors arising from age-related issues and ovulatory disorders account for another 30%. Around 20% of cases involve male and female fertility factors, or combined infertility. In the remaining 20% of cases, it may not be possible to identify a precise medical cause for infertility. It is estimated 1 in 4 couples will suffer from an unknown or unexplained fertility issue.

Common causes of infertility in women

Problems with ovulation, the monthly release of an egg by the ovaries, is the main cause for infertility in women. Some conditions completely prevent the release of an egg, and others can result in inconsistent ovulation. Specific causes, roughly in order of prevalence, are:

Ovulation disorders

Disorders which stop or disrupt ovulation (the release of an egg each month from the ovaries), such as polycystic ovarian syndrome (PCOS) can make it difficult to get pregnant. PCOS is the most common ovulation disorder, in which there is hormonal imbalance that disrupts the reproductive cycle, leading to irregular or even completely absent periods. One of the main characteristics of PCOS is the presence of a multiple immature ovarian follicles. The NHS estimates that this condition affects about one in 10 women in the UK. Many may remain undiagnosed because they are asymptotic, aside from having difficulty in getting pregnant.


For women, fertility decreases naturally with age. From the age of 35, it begins to decline at a much quicker pace. From the age of 40, there is a less than 10% chance of getting pregnant naturally each month. The chances of conceiving naturally continue to get smaller with age until the menopause is reached, normally between the ages of 45 to 55. Advanced maternal age is one of the main causes of infertility in developed countries, leading to a lower ovarian reserve and poorer egg quality. As a result, pregnancy rates decrease and the chances of miscarriage are higher. All these factors combined lead to lower live birth rates.


Endometriosis is a chronic condition where tissue usually found within the womb lining grows outside the womb. This can cause varying degrees of infertility depending on its severity. Endometriosis can cause anatomical distortions that can impair the function of the ovaries, fallopian tubes and uterus. Studies have also shown a correlation between infertility and endometriosis due to a poorer egg quality in women suffering from this condition. Although 30 – 50% of women with endometriosis experience fertility issues, 50% are able to conceive without any difficulty.


Fibroids are benign growths that can occur inside the uterus. They are very common, estimated to affect as much as 77% of women of reproductive age. Larger fibroids can reduce fertility by causing blockages or anatomical distortions. There are several different ways to treat fibroids, ranging from the oral contraceptive pill to surgical procedure to remove the growths (known as a myomectomy). The most effective treatment can be assessed by a gynaecologist based on size, number and position of the fibroids.

Sexually transmitted infections (STI)

Left untreated, certain sexually transmitted infections can lead to infertility. Chlamydia and gonorrhoea are among the most prevalent yet most preventable STIs that can cause infertility. Both are bacterial infections that spread to the reproductive organs and cause pelvic inflammatory disease (PID). If detected and treated early, most STIs do not have any long-term effects on fertility.

Chronic illnesses

Long-term conditions such as diabetes, thyroid disease, asthma and depression have all been linked to fertility problems. If you are affected by a chronic disease, it’s recommended that you consult your GP before you start trying to conceive.

Specific medication and drug use

Medication used to treat specific conditions, such as antidepressants, can become a cause for infertility. If you are unsure, it is best to consult your GP. The use of illegal drugs can also disrupt the reproductive hormone cycle and make it difficult to get pregnant.

Common causes of infertility in men

For men, infertility generally stems from issues with the quality or quantity of sperm. These could be a result of testicular damage or problems with the delivery of sperm due to ejaculatory, obstructive or secretory disorders. The most common causes of infertility are:

Low sperm count (oligozoospermia)

A low sperm count is considered to be anything less than 15 million sperm per millilitre of semen. It may still be possible to conceive with a reduced sperm count, but it is likely to take longer. There are many factors that can contribute towards a low sperm count, including hypogonadism, sexually transmitted infections like chlamydia and gonorrhoea, as well as certain lifestyle choices like smoking tobacco, excessive alcohol consumption and the use of marijuana. Many men with a low sperm count are able to improve their chances of conceiving by making healthier lifestyle choices.

No sperm count (azoospermia)

Azoospermia refers to when there is no sperm present in a man’s ejaculate. It is estimated that 1 in 10 men experiencing infertility are azoospermic. There are two different types of azoospermia: obstructive azoospermia and non-obstructive azoospermia. Obstructive azoospermia is where there is a blockage stopping the sperm from reaching the semen, while non-obstructive azoospermia refers to a decreased production of sperm by the testicles, or failure of spermiogenesis.

Abnormal sperm morphology

Sperm morphology refers to the shape and size of the individual sperm cells. Normal sperm have a oval-like head and a long tail, which allows them to swim. Abnormal sperm may have a detached or misshapen head, or a coiled or split tail. Such abnormalities can impede their ability to move and penetrate the egg. This lowers the chances of fertilisation. Although rarely a cause of infertility on its own, sperm morphology is an important part of a routine semen analysis.

Erectile dysfunction

Erectile dysfunction is an often overlooked cause of infertility. It is common, affecting 1 in 5 men in the UK. As healthy sexual function is an essential first step in the process of reproduction, erectile dysfunction can severely limit the chances of conceiving. While the effects of ED can often be alleviated by medication and healthy lifestyle changes, there are also surgical treatment options.

Obesity or a high BMI (30+)

For both men and women, having a BMI over 30 can hinder your chances of conceiving. Although the relationship between weight and fertility is complex and should be assessed on a case-by-case basis, men and women with a BMI between 18 – 25 have been shown to have better chances of conceiving and higher chances of success with ART.

Undescended testicles (cryptorchidism)

The testicles are important male reproductive organs that generate sperm. Male babies are normally born with both testicles located in the scrotum, however sometimes one testicle (unilateral) or both testicles (bilateral) is inside the groin or lower abdomen. Usually, the undescended testicle(s) will move to the proper position by the time the baby is three months old, by which point they begin to develop the cells that will go on to support spermiogenesis. Undescended testicles negatively affect important testicular development in infancy, which can impair fertility later in life.

Physical trauma or surgery to the testicles

Physical trauma to the testicles, also known as testicular trauma, can cause infertility in men. It’s normally the result of accidental physical damage to the testicular tissue. In some cases, treatment for certain testicular conditions may require surgery, which can also have a permanent effect on fertility. 

Genital tract infections

Male genital tract infections account for roughly 15% of cases of male infertility.

Lifestyle factors

For both men and women, ovulation and spermiogenesis (the production of healthy sperm) can be seriously affected by certain environmental factors and lifestyle choices. These include:

  • Obesity: Having a BMI of 30 or more reduces fertility for both men and women. For women, being very underweight can also affect ovulation. Obesity has also an impact in IVF success rates and increases the risk of complications during the pregnancy for both mother and baby.
  • Infections: Chlamydia and other sexually transmitted infections can reduce fertility.
  • Smoking: Smoking tobacco reduces semen quality and can negatively affect egg quality. Smoking also endangers the foetus if conception does take place. Learn more about the dangers of smoking during preconception here.
  • Alcohol consumption: Excessive alcohol consumption, as well as the use of recreational drugs, can negatively affect fertility and pose a risk to a developing foetus.
  • Exposure to environmental hazards: Environmental hazards and industrial toxins, such as pesticides and solvents, can damage fertility, as can certain medications such as anabolic steroids and corticosteroids. You should always discuss the implications of any prescription medication with your GP if you are trying to get pregnant.

What are the main causes of male infertility?

What are the main causes of female infertility?

You're experiencing infertility. What happens next?

If you’ve been trying to conceive for over a 12 months, or for women over 35 for six months, without success, it’s time to seek help. There are are various treatment options available that can help even the most severe cases of infertility. For example:

In Vitro Fertilisation (IVF)

Intrauterine Insemination (IUI)

Donor IVF

What type of injuries affect the fallopian tubes?

Around 25% of cases of female infertility are caused by blockages inside the fallopian tubes. Normally the fallopian tubes collect the egg during ovulation as it is released from the ovaries. The sperm reach and fertilise the egg inside the fallopian tubes. Damaged or obstructed fallopian tubes prevent this movement so fertilisation cannot take place. Fallopian tubes can be damaged by:

  • Pelvic infections caused by a sexually transmitted infection (STI) such as chlamydia or gonorrhoea
  • Previous surgery such as appendectomy which may cause scar tissue and adhesions within the pelvis
  • Benign endometriosis growths
  • Previous history of ectopic pregnancy, in which a fertilised egg implants inside the fallopian tube

What is endometriosis and how many women are affected by it?

There is a strong relationship between endometriosis and sub fertility. While some 10% of women of reproductive age suffer from endometriosis, it’s estimated up to 50% of women with fertility problems have endometriosis.

The condition gets its name from the word endometrium, which is the tissue that lines the inside of the womb and which is shed each month during menstruation. Endometriosis is caused by the presence of this tissue in places other than the uterus. It is most frequently found in the ovaries, fallopian tubes, the ligaments which support the uterus and the lining of the pelvic or abdominal cavity. This tissue behaves in a similar way to the endometrium and is sensitive to hormonal changes during menstruation. This is the source of the symptoms associated with the disease. Although some patients may not have any symptoms, the most common symptoms are pain, heavy periods and infertility. Pain may only occur during menstruation, but there can also be gastrointestinal and urinary symptoms if endometrial tissue invades other areas such as the intestine, the bladder or the colon.

Endometriosis-related infertility can arise from anatomical changes in the pelvis. Endometriosis can cause growths that obstruct the fallopian tubes and can contribute towards the formation of ovarian cysts. These may sometimes require surgery, which can result in the loss of ovarian tissue and decreased fertility. There are medical and surgical treatments available and in many cases the chances of getting pregnant depend on the progression of the disease.

How is endometriosis detected?

Endometriosis is usually diagnosed by undergoing a surgical procedure called a laparoscopy. If endometriosis is present in the ovaries it can be sometimes be detected using ultrasound. Ovarian cysts caused by endometriosis are known as a chocolate cysts or endometriomas.

If I have severe endometriosis, can I start fertility treatment without having surgery?

Whether or not surgery is required before fertility treatment is something that you will need to discuss with your consultant. It will depend on the severity of the endometriosis, your ovarian reserve and how the affected ovary responds to medication. IVF can be a very effective treatment option for endometriosis-related infertility in cases where other techniques have not been successful.

There is a common belief that pregnancy can cure endometriosis. This is not true, but the symptoms of endometriosis may be temporarily suppressed during pregnancy due to hormonal changes. After giving birth, symptoms are very likely to return.

What are polycystic ovaries?

Around 20% of women have polycystic ovaries (PCO). The term refers to an increased number of dormant follicles, also known as antral follicles, which are tiny small fluid-filled sacs on the surface of the ovary. These can be detected with an ultrasound scan. Many women with PCO have no problems ovulating and getting pregnant. However, some women who have this condition also suffer from Polycystic Ovarian Syndrome (PCOS). Women with PCOS have irregular menstrual cycles or may not ovulate at all, which leads to difficulty getting pregnant.

Why does anovulation happen?

Anovulation is when the ovaries fail to produce, mature or release an egg.

Factors that can contribute to anovulation include: stress, significant weight gain or loss, excessive production of prolactin (the hormone responsible for producing breast milk) and polycystic ovaries. Approximately 35% of women experience anovulation at some time during their lives. The origin of this hormonal disorder may be in the hypothalamus, a part of the brain that controls hormonal function, the pituitary gland, or in the ovary itself.

How is male infertility analysed?

To study male fertility, the number, motility and shape of the spermatozoa are analysed. The World Health Organization (WHO) reference values for a normal semen analysis is a sperm count of at least 15 million sperm per ml, with at least 32% of the sperm having progressive motility and at least 4% having a normal shape. If the sperm count or motility is lower than this the chances of a pregnancy occurring naturally is reduced.

What are the causes of a low sperm count?

The main causes of a low sperm count are:

  • Hormonal imbalances caused by glands in the brain (the pituitary gland and the hypothalamus) which regulate spermiogenesis
  • Genetic disorders such as Klinefelter syndrome, in which there is an alteration in the Y-chromosome that affects the formation of sperm
  • Testicular problems such as developmental issues, anomalous development or undescended testicles
  • Lifestyle choices such as excessive alcohol consumption, smoking of tobacco and marijuana use

What kind of abnormalities can occur in sperm?

Spermatozoa can show anomalies in their motility (astenozoospermia), shape (teratozoospermia) or vitality (necrozoospermia).

What are the main causes of abnormalities in sperm?

Semen abnormalities can be caused by a range of factors, including:

  • Infections or the presence of certain antibodies
  • Alterations in the number of chromosomes; DNA fragmentation; oxidation phenomena; varicocele, etc.
  • Diabetes, thyroid disorders, kidney disease, certain medications, drugs, tobacco and stress.

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