By Zaira Salvador BSc, MSc (embryologist), Andrea Rodrigo BSc, MSc (embryologist), Sara Salgado BSc, MSc (embryologist) and Gorka Barrenetxea Ziarrusta MD, PhD (gynecologist).
Last Update: 10/24/2018

In order to find the cause of infertility in a couple, it is necessary to run a series of tests. With the results, it is possible to determine whether the cause has a male, female, or mixed origin.

In general, the most common causes of infertility in males and females are:

  • Advanced maternal age (more than 35-40)
  • Damage to the Fallopian tubes
  • Sperm production abnormalities
  • Erection problems in males
  • Extreme obesity
  • Endometriosis
  • Genital tract disorders
  • Other causes: sexually transmitted diseases, medications, cancer, thyroid diseases, fibroids

In the following sections, you will find a detailed analysis of the main causes of sterility in humans, classified into female and male origin.

The different sections of this article have been assembled into the following table of contents.

Main causes of infertility in couples

Infertility issues in couples can be caused by the man, the woman, or both. Statistics show a similar frequency, with 30% of the cases having a male origin, and another 30% a female one.

The remaining 40% can be distributed between mixed or combined causes, which occurs in 20% of the cases, and unexplained infertility, present in another 20%. Mixed infertility causes mean that both members of the couple have infertility issues, while unexplained infertility actually refers to the impossibility of the cause to be detected in spite of running the appropriate tests.

Female infertility

When it comes to female infertility, the causes may be varied but interrelated, and may be caused by different factors. Thus, a woman can have any of the following dysfunctions:

Ovary problems
Due to either problems with ovulating, or poor egg quality.
Tubal factor
Due to Fallopian tube problems, which can prevent or hinder the passage of the oocyte and the sperm.
Cervical factor
Problems with the cervix, which can hinder or even block the pathway of sperm toward the egg.
Uterine factor
Uterine fibroids, uterine adhesions, uterine abnormalities, poor endometrial development…

You may also enjoy some further information reading this: What Causes Female Infertility? – Definition, Signs & Treatment.

Ovarian causes

Hormonal alterations in the menstrual cycle of the woman can prevent ovulation (i.e. anovulation), cause it to occur in the wrong moment, or occurs but the eggs are produced incorrectly.

The endocrine system is responsible for controlling the ovarian cycle. For this reason, alterations caused by stress, obesity, low weight, thyroid gland problems, medications, etc. can affect the normal functioning of the ovary.

To examine the ovary and ovulation, the specialist runs a series of ultrasounds and hormonal blood tests to look for potential pathologies that may be causing infertility in the patient.

Tubal causes

By tubal factor infertility we refer to any abnormality or dysfunction that appears in the Fallopian tubes of females. This organs allows two major events: the egg-sperm binding, and the journey of the embryo to the uterus.

Thus, if the tubes do not carry out their function, the woman will be infertile. This happens when block tubes are blocked due to a variety of reasons, such as salpingitis, malformations, hydrosalpinx, endometriosis, etc.

In order for a diagnosis of tubal problems to be rendered, performing a hysterosalpingography (HSG) is necessary. This is an essential test when it comes to evaluating female fertility. As long as tubal patency exists in one tube, that is, as long as one tube is not blocked, pregnancy can take place.

Cervical causes

If sperm cannot go through the cervix, they will never reach the egg. Abnormal growths in this part of the female reproductive system, including polyps or fibroids, along with abnormalities of the cervical mucus can lead to infertility in the woman.

Uterine causes

Uterine abnormalities, including malformations or endometrial problems, can cause infertility issues by preventing implantation or a full-term pregnancy.

Amongst the most common uterine causes of infertility, we can mention endometriosis, fibroids, and polyps. Read more: Uterine Factor Infertility – Diagnosis, Characteristics & Treatment.

Male infertility

As regards male infertility, there exist four types depending on the cause:

Pre-testicular factor
Due to hormonal imbalances, the testes are not fully developed or are unable to carry out their function.
Testicular factor
Testicular disorders, whether congenital (from birth) or acquired.
Post-testicular factor
Including abnormalities of the seminal ducts, sexual impotence, or any kind of urinary tract infection.
Sperm disorders
All types of alterations in sperm parameters.

Click here to read more: What Causes Male Infertility? – Symptoms, Treatment & Statistics.

Pre-testicular causes

It includes hormonal causes due to a poor endocrine regulation. As a result, the development of any of these parts can be altered:

A blood test for hormone levels is the only test that is able to detect pre-testicular causes of male infertility.

Testicular causes

It refers to any kind of disorder or defect in the testes, whether congenital or acquired.

Congenital defects
Usually due to genetic abnormalities, like the Klinefelter syndrome.
Acquired defects
They can be caused by medications, drugs, infections, trauma, or conditions, like varicocele or orchitis.

Post-testicular causes

This type of infertility is due to abnormalities or disorders in the seminal ducts, which include the epididymis, vasa deferentia, and urethra. Sperm must go through this pathway before being released with ejaculation.

In this case, infertility can be due to infections, blockages, or trauma. All of them can prevent sperm from being ejaculated.

Sperm disorders

The leading cause of male infertility. It is due to disorders in the sperm, whether they affect their morphology, vitality, or count.

The following are the most common sperm disorders:

Oligospermia or oligozoospermia
Low sperm count.
Asthenozoospermia
Poor sperm motility.
Teratospermia or teratozoospermia
High amount of abnormally shaped sperm.
Necrospermia or necrozoospermia
Elevated presence of dead sperm.
Azoospermia
Zero sperm count.

The only method to detect the presence of a sperm disorder is a semen analysis, also known as seminogram or sperm test.

Mixed causes of infertility

In some cases, childlessness is present in both partners. In other words, the cause(s) of infertility will be the result of combining any of the male and female infertility issues mentioned above.

Nonetheless, in some cases infertility is due to immunological incompatibility. In these cases, the immune system of the woman attacks the sperms of the man. For this reason, it is possible that both members are fertile is examined individually, but together conception is not possible unless they seek medical assistance.

According to Dr. Gorka Barrenetxea, Obstetrician & Gynecologist specialized in Reproductive Medicine:

It is common for us to find abnormalities in both members of the couple, including a sperm count under the normal reference values, a diminished ovarian reserve, tubal problems, etc.

Unexplained infertility

When the cause of infertility is unclear, we refer to it with the term unexplained infertility or unknown infertility. It occurs in approximately 20% of the cases. In spite of performing the appropriate tests, specialists fail to find a cause that explains why the woman is not getting pregnant.

Unexplained infertility does not translate into absence of fertility issues, but into unavailability of specific tests that allow the detection of whatever is causing infertility in the couple. Some cases are so challenging that the different tests available nowadays are insufficient to find the actual cause of sterility.

The good news is that unknown infertility can be tackled with Assisted Reproductive Technology (ART) as well, namely Intrauterine Insemination (IUI) or In Vitro Fertilization (IVF).

Considering undergoing a fertility treatment? "The Calculator" selects several clinics for you out of the pool of clinics that meet our strict quality criteria. Moreover, it will offer you a comparison between the fees and conditions each clinic offers in order for you to make a well informed choice.

FAQs from users

Can low sperm volume cause infertility?

By Zaira Salvador BSc, MSc (embryologist).

Only if it comes along with other sperm abnormalities, such as low sperm count, poor sperm motility, and/or abnormal sperm morphology. When it is only a case of hypospermia, these males are still able to achieve pregnancy, either naturally or by means of ART.

Can HPV cause infertility in males?

By Zaira Salvador BSc, MSc (embryologist).

Some studies link the infection of semen with HPV to an impairment of sperm parameters, which suggests a potential role in male infertility, particularly in sperm motility. Also, it has been related to an increased risks of miscarriage among couples undergoing IVF, especially when HPV DNA was found in the semen sample of the male partner.

Can Chlamydia cause infertility in males?

By Zaira Salvador BSc, MSc (embryologist).

Yes, recent studies have shown that Chlamydia can harm the quality of the male sperm, as the degree of sperm fragmentation in these men’s sample is almost three times higher than in healthy males. Poor sperm motility, having defective shapes, or a low sperm count are the sperm parameters that could be affected by a Chlamydia infection.

Do cats or dogs cause infertility in humans?

By Andrea Rodrigo BSc, MSc (embryologist).

To date, there is no evidence of a link between common pets and infertility. Having dogs, cats, hamsters or others will not affect your fertility. However, there exist certain parasitic infections that can be passed from them to humans and might have a negative impact on human fertility. As for cat allergy, there exist no studies that show a link between it and human infertility either.

On the other hand, people who work with livestock could be infected with certain diseases such as brucellosis, which symptoms include fever, chills, aches, sweating… In short, it might cause the body not to work optimally, and therefore affect a couple’s reproductive efforts.

Can birth control cause female infertility?

By Sara Salgado BSc, MSc (embryologist).

Women who have been using hormonal contraception for a long period of time can take several month to recover normal menstrual cycles, and therefore their fertility. So the answer is yes, hormonal contraceptives can cause temporary infertility in females.

What are the causes of infertility at age 40?

By Sara Salgado BSc, MSc (embryologist).

In couples where the woman is 40 or older, it is likely that the cause of infertility is due to ovary problems associated with advanced maternal age. It is quite common for women at this stage in their reproductive years to experience hormonal imbalances that cause their menstrual cycle to develop inadequately. Moreover, the ovarian reserve experiences a dramatical decrease from age 35 onwards.

Does autoimmune thyroiditis cause infertility?

By Zaira Salvador BSc, MSc (embryologist).

Yes, autoimmune thyroiditis, also known as Hashimoto’s disease, is the most common cause of hypothyroidism. The woman’s body makes antibodies that attack the thyroid gland. As a result, a decrease in the amount of thyroid hormones occurs, causing irregularities in the menstrual cycle, among others.

You may also enjoy some further information reading this: Impact of Thyroid Hormones on Female Fertility.

Can stress cause female infertility?

By Zaira Salvador BSc, MSc (embryologist).

Yes. As a matter of fact, in todays modern, fast-paced society, it is a common cause leading to female and male infertility. In the case of women, the presence of a adrenalin can signal to the body that it is not the right time for conception, thereby preventing pregnancy.

Adrenalin also causes the pituitary gland to produce prolactin. This can cause infertility by inhibiting the releasing of GnRH, a hormone responsible for the production of sex hormones, may suppress ovulation.

Can Chlamydia cause infertility forever?

By Zaira Salvador BSc, MSc (embryologist).

If untreated, Chlamydia can affect a woman’s fertility in many ways. If the infection spreads from the vaginal canal into the uterus, it can cause pelvic inflammatory disease (PID) and the endometrium to swell and scar. In most severe situations, this scar tissue can prevent implantation or cause an ectopic pregnancy.

Can drinking cause infertility?

By Zaira Salvador BSc, MSc (embryologist).

Yes, it can. According to some doctors, it lowers testosterone levels in mens, and decreases the quality and the quantity of sperm. In fact, it some cases, it can affect libido in males and females, as well as cause impotence in men.

Can HPV cause infertility in females?

By Zaira Salvador BSc, MSc (embryologist).

The human papillomavirus (HPV) alone should not have a huge impact on fertility. Although some studies have found that IVF patients who screened positive for HPV were less likely to have a baby, the reasons behind this affirmation are still unclear.

Some investigations have found that it is because an embryo might find it harder to implant in a woman whose immune system is unable to clear the virus. However, the vast majority are able to get pregnant without problems.

Can uterus didelphys cause infertility?

By Zaira Salvador BSc, MSc (embryologist).

Uterus didelphys rarely causes problems. In fact, some women don’t even know they have it, while others experience very painful menstrual periods. Uterus didelphys can be the cause of recurrent miscarriages. Though rarely, if the woman gets pregnant with fraternal twins, they might be delivered hours or days apart.

Does mumps cause infertility in males?

By Zaira Salvador BSc, MSc (embryologist).

Childhood diseases such as mumps or chicken pox normally run their course and end without significant long-term effects. However, when a boy or an adult man contracts mumps, it can affect the testes and cause a condition called orchitis.

The prevalence of orchitis in young adults and adults ranges from 20% to 30%. Only in a small percentage of mumps-induced orchitis, the male experiences a reduction in sperm production, probably linked to changes in male hormones during the earliest stages of orchitis.

Can a sedentary lifestyle cause infertility?

By Zaira Salvador BSc, MSc (embryologist).

A sedentary lifestyle is not beneficial in any way, especially for women than men. Several studies suggest that a sedentary lifestyle as a teenager can cause hormonal imbalances and anovulatory cycles, consequences more commonly seen in PCOS patients. In the case of men, those with a sedentary lifestyle tend to be overweight or even obese, which leads to low sperm quality. So, in short, to prevent infertility you should stay active and eat right.

Suggested for you

If you have just received a diagnosis of infertility and been referred to fertility treatment, you might feel a bit overwhelmed due to so much new information. You can learn more here: What is Assisted Reproductive Technology (ART)? – Techniques & Costs.

Throughout this post, what you found is a brief summary of the different causes of male and female infertility. If you wish to delve deeper into the tests performed to identify them, we recommend that you visit any of these posts:

Finally, one of the most concerning aspects for patients who are going to start a fertility treatment is whether it will actually work for them. You can clarify your doubts here: Success Rates in Assisted Reproduction.

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References

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Reproducción Asistida ORG. Video: ¿Es posible que ambos miembros de la pareja sean infértiles? (Can both members of the couple be infertile?), by Gorka Barrenetxea, MD, PhD, Oct 3, 2017. [See original video in Spanish].

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World Health Organization 1992b WHO laboratory manual for the examination of human semen and sperm–cervical mucus interaction. Cambridge University Press. Cambridge, UK.

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Authors and contributors

 Zaira Salvador
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia (UPV). Embryologist specializing in Assisted Procreation, with a Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI). More information
License: 3185-CV
 Andrea Rodrigo
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information
 Sara Salgado
BSc, MSc
Embryologist
Degree in Biochemistry and Molecular Biology from the University of the Basque Country (UPV/EHU). Master's Degree in Human Assisted Reproduction from the Complutense University of Madrid (UCM). Certificate of University Expert in Genetic Diagnosis Techniques from the University of Valencia (UV). More information
 Gorka Barrenetxea Ziarrusta
Bachelor's Degree in Medicine & Surgery from the Public University of Navarra, with specialty in Obstetrics and Gynecology from the University of the Basque Country. He has over 30 years of experience in the field and works as a Titular Professor of Obstetrics & Gynecology at the University of the Basque Country and the Master's Degree in Human Reproduction of the Complutense University of Madrid. Vice-president of the SEF. More information
License: 484806591
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