Causes of Infertility: Common Reasons in Women and Men

When pregnancy does not happen as expected, it is natural to wonder why. Could there be a problem with ovulation, the fallopian tubes, sperm health, hormones, or something else?

Infertility can have several different causes. It may be related to the female reproductive system, the male reproductive system, a combination of factors affecting both partners, or a cause that cannot be identified with current testing.

Understanding the possible causes of infertility is a helpful first step towards knowing what questions to ask and when to seek medical advice. It is important to remember that fertility difficulties are not necessarily anyone's fault, and a medical assessment is often needed to understand what may be contributing to them.

What Causes Infertility?

Infertility occurs when a person or couple experiences difficulty achieving pregnancy. The World Health Organization (WHO) defines infertility as the failure to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse.

There is no single cause of infertility. Conception depends on several processes working together, including the release of an egg, the production and movement of sperm, fertilisation, and the ability of an embryo to develop and implant.

A problem affecting any of these processes may make pregnancy more difficult.

The main categories of infertility factors are:

• Female factors: Conditions affecting ovulation, the ovaries, fallopian tubes, uterus or reproductive hormones.
• Male factors: Problems with sperm production, sperm quality or the passage of sperm.
• Combined factors: Fertility difficulties involving both partners.
• Unexplained infertility: When standard investigations do not identify a clear cause.

The WHO recognises all of these categories. The cause can sometimes be identified through appropriate investigations, although in other cases it remains uncertain.

Causes of Infertility in Women

Female infertility can be associated with several reproductive and hormonal conditions. More than one factor may be present at the same time.

1. Problems With Ovulation

Ovulation is the process in which an ovary releases an egg. For pregnancy to occur naturally, an egg must be released and be available for fertilisation.

If ovulation happens irregularly or does not happen, conception may be more difficult.

Possible reasons for ovulation problems include:

• Polycystic ovary syndrome (PCOS).
• Certain hormonal conditions, including thyroid disorders.
• Conditions affecting the hormones that regulate the ovaries.
• Reduced ovarian function.
• Significant changes in body weight or excessive exercise in some circumstances.

Irregular or absent periods can sometimes indicate an ovulation problem, although menstrual changes can have other causes too.

2. Polycystic Ovary Syndrome (PCOS)

PCOS is a hormonal condition that can affect menstrual cycles and ovulation. Some women with PCOS release eggs less regularly, which can make it harder to conceive.

However, having PCOS does not automatically mean a woman cannot become pregnant. Many women with PCOS conceive naturally or with appropriate medical support.

If periods are irregular or absent, a healthcare professional can assess whether PCOS or another condition may be affecting ovulation.

3. Reduced Ovarian Reserve and Egg-Related Factors

Ovarian reserve refers to the remaining supply of eggs in the ovaries. It generally declines with age, although the rate of change varies between individuals.

Reduced ovarian reserve may affect the response to fertility treatment. However, it does not by itself determine whether a woman can conceive naturally.

Egg quality is also important. As women age, the proportion of eggs with chromosomal abnormalities tends to increase, which can affect fertilisation, embryo development and the chance of a successful pregnancy.

Tests such as anti-Müllerian hormone (AMH) and antral follicle count (AFC) can help assess aspects of ovarian reserve. They cannot, on their own, predict with certainty whether someone will become pregnant.

4. Blocked or Damaged Fallopian Tubes

The fallopian tubes connect the area around the ovaries to the uterus. They provide the usual location for fertilisation and allow the early embryo to travel towards the uterus.

If the tubes are blocked or damaged, sperm may not be able to reach the egg, or the fertilised egg may have difficulty travelling through the tube.

Possible causes include:

• Previous pelvic infections, including some sexually transmitted infections.
• Pelvic inflammatory disease.
• Endometriosis.
• Previous pelvic or abdominal surgery.
• Scar tissue affecting the reproductive organs.

A test called a hysterosalpingography (HSG) may be recommended to assess whether the fallopian tubes are open.

5. Endometriosis

Endometriosis occurs when tissue similar to the lining of the uterus grows outside the uterus. It may cause pelvic pain, painful periods and, in some people, fertility difficulties.

Depending on its location and severity, endometriosis may affect the ovaries, fallopian tubes or the surrounding pelvic environment.

Not everyone with endometriosis experiences infertility, and the effect on fertility varies from person to person.

6. Uterine Conditions and Fibroids

The uterus plays an important role in pregnancy because an embryo usually implants in its lining.

Certain uterine conditions may affect the chances of conception or a pregnancy continuing. These can include particular types of fibroids, abnormalities in the shape of the uterus, and scar tissue inside the uterine cavity.

The effect depends on the type, size and location of the condition. Not every fibroid causes fertility problems, and treatment decisions need to be based on an individual assessment.

7. Hormonal Disorders

Reproductive hormones help regulate ovulation and the menstrual cycle. Conditions affecting the thyroid, pituitary gland or other parts of the hormonal system may interfere with these processes.

Hormonal conditions can sometimes be treated, but the appropriate approach depends on the underlying cause.

A healthcare professional may recommend blood tests or other investigations when symptoms or medical history suggest a hormonal problem.

Causes of Infertility in Men

Male fertility depends on producing sperm, maintaining appropriate sperm function, and allowing sperm to travel through the reproductive tract and be released during ejaculation.

Male factors can contribute to fertility difficulties even when a man feels healthy and has no obvious symptoms.

1. Low Sperm Count

Sperm count refers to the number of sperm present in a semen sample. A lower-than-expected sperm count may reduce the probability of sperm reaching and fertilising an egg.

A semen analysis is commonly used to assess sperm concentration and other characteristics. A single result does not always provide the complete picture, and a clinician may recommend repeating the test.

2. Poor Sperm Motility

Sperm motility describes how sperm move. Sperm generally need to move effectively to travel through the female reproductive tract and reach an egg.

Reduced sperm motility can make fertilisation more difficult. It may occur alongside other changes in semen parameters.

3. Abnormal Sperm Morphology

Sperm morphology refers to the size and shape of sperm. Certain abnormalities may be associated with reduced fertility.

Morphology should not be interpreted in isolation. A semen analysis report needs to be considered alongside sperm count, motility, medical history and other relevant findings.

4. Problems With Sperm Production

The testicles produce sperm, and several conditions can interfere with this process.

Possible contributors include:

• Hormonal disorders.
• Genetic conditions.
• Certain infections or injuries.
• Varicocele, which involves enlarged veins in the scrotum.
• Previous or current medical treatments, including some cancer treatments.
• Use of anabolic steroids, which can suppress sperm production.

Some causes may be treatable, while others require specialist assessment and a discussion of available fertility options.

5. Blockages in the Male Reproductive Tract

In some men, sperm are produced but cannot travel normally through the reproductive tract because of a blockage.

Blockages may be associated with previous infections, injury, surgery or conditions present from birth.

The appropriate investigations and treatment depend on where the blockage is located and what caused it.

6. Hormonal and Ejaculation Problems

Hormones such as testosterone are involved in male reproductive function, but fertility depends on a balance of signals between the brain and the reproductive organs.

Certain hormonal disorders can affect sperm production. Problems with ejaculation or the delivery of semen can also make natural conception more difficult.

Importantly, taking testosterone supplements or injections without medical guidance can suppress sperm production in some men. Men who are trying to conceive should discuss testosterone treatment with a qualified healthcare professional.

Can Both Partners Have Fertility Problems?

Yes. Fertility difficulties can involve factors affecting one partner or both partners.

For example, one partner may have irregular ovulation while the other has reduced sperm motility. In other situations, investigations may identify a factor in only one partner.

This is why fertility assessment often involves both partners rather than assuming the problem lies with the woman.

A balanced assessment can help identify which investigations are appropriate and avoid unnecessary delays.

Can Lifestyle Factors Affect Fertility?

Some lifestyle factors are associated with reduced fertility in women and men. These may include:

• Smoking or tobacco use.
• Excessive alcohol consumption.
• Obesity or significant problems with body weight.
• Use of anabolic steroids.
• Exposure to certain environmental toxins.
• Some medicines or medical treatments.

The effects vary according to the exposure, the person's health and other circumstances. Lifestyle factors are not the explanation for every case of infertility, and a person should not assume that fertility difficulties are the result of something they did wrong.

If you are planning a pregnancy, a healthcare professional can advise you on relevant lifestyle changes, medicines and medical conditions. Do not stop prescribed medication without discussing it with your clinician.

What Is Unexplained Infertility?

Sometimes, initial fertility investigations do not identify a clear reason why pregnancy has not occurred. This is commonly called unexplained infertility.

It does not mean that the difficulty is imaginary or that no biological factors are involved. It means that the tests performed have not established a definite explanation.

Further evaluation or treatment may be considered depending on factors such as age, how long pregnancy has been attempted, medical history and the results of previous investigations.

You can learn more in our related article: Unexplained Infertility.

How Are the Causes of Infertility Identified?

There is no single test that identifies every possible cause of infertility. The assessment is guided by medical history, symptoms, age and how long pregnancy has been attempted.

Depending on the circumstances, investigations may include:

• A review of menstrual cycles, previous pregnancies and medical history.
• Blood tests to assess selected hormones.
• Ultrasound examination of the reproductive organs.
• Tests to assess whether the fallopian tubes are open.
• Semen analysis to evaluate sperm concentration, movement and shape.
• Additional investigations when a particular condition is suspected.

Not everyone needs every test. A fertility specialist can explain which investigations are appropriate and what the results can and cannot tell you.

When Should You Seek Medical Advice?

Consider seeking medical advice if you have been trying to conceive without success, have irregular or absent periods, have a known reproductive condition, or have concerns about your fertility.

The World Health Organization uses 12 months of regular unprotected sexual intercourse without achieving pregnancy as its definition of infertility. However, you may be advised to seek an assessment earlier depending on your age, medical history or known risk factors.

Both partners can benefit from being involved in the assessment.

Does Knowing the Cause Mean Infertility Can Be Treated?

Identifying a cause can help a healthcare professional discuss suitable options. Depending on the diagnosis, these may include treatment for an underlying condition, medication to support ovulation, surgery in selected cases, intrauterine insemination (IUI), in vitro fertilisation (IVF), or other approaches.

Not every cause can be fully corrected, and no treatment guarantees pregnancy. The right approach depends on the individual circumstances and the findings of the assessment.

A Final Word

Discovering that pregnancy is taking longer than expected can be worrying. But fertility difficulties are not always straightforward, and there is no reason to assume that one partner is to blame.

Female factors, male factors, a combination of factors or an unexplained cause may all play a role. Understanding the possibilities and seeking appropriate medical advice can help you make informed decisions about the next steps.

At Dream Baby, our aim is to make fertility information easier to understand, so that you can approach your questions with greater knowledge and confidence.

Frequently Asked Questions

What is the most common cause of infertility in women?

There is no single cause that applies to every woman. Ovulation disorders, including those associated with PCOS, are important causes, but tubal, uterine, age-related and other factors can also contribute.

What are common causes of infertility in men?

Possible causes include low sperm count, reduced sperm motility, abnormal sperm morphology, hormonal disorders, problems with sperm production and blockages in the reproductive tract.

Can a woman be infertile even if she has regular periods?

Yes. Regular periods can be consistent with ovulation, but they do not rule out other fertility factors, such as blocked fallopian tubes or certain uterine conditions.

Can a man have fertility problems without symptoms?

Yes. Some male fertility problems have no obvious symptoms and may only be identified through medical assessment and semen analysis.

Can lifestyle changes reverse infertility?

Lifestyle changes may improve some aspects of reproductive health, but they cannot correct every cause of infertility. The potential benefit depends on the underlying factors.

Does infertility always mean IVF is necessary?

No. IVF is one of several possible treatment options. Some people may conceive without assisted reproduction, while others may benefit from different treatments depending on their diagnosis.

Where to Go Next

If you would like to understand infertility in more detail, explore these related Dream Baby articles:

• What Is Infertility? — Understand the definition and different types of infertility.
• Primary vs Secondary Infertility — Learn what these terms mean.
• Unexplained Infertility — Understand what it means when investigations do not identify a clear cause.
• When Should You See a Fertility Specialist? — Learn when an assessment may be appropriate.
• What Happens at a Fertility Consultation? — Find out what to expect at an initial appointment.

Medical information note: This article is for general educational purposes only and is not a substitute for individual medical advice, diagnosis or treatment. This article has not been medically reviewed by a Dream Baby doctor. Please consult a qualified healthcare professional for advice about your circumstances.

Sources

• World Health Organization (WHO), Infertility — Fact Sheet, 28 November 2025.
• World Health Organization (WHO), Guideline for the prevention, diagnosis and treatment of infertility, 2025.