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

Causes of 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