Infertility Causes

Infertility causes are the medical, hormonal, genetic, lifestyle, environmental, and structural factors that make it harder for a couple to conceive. In men’s health, this often means problems with sperm production, sperm movement, ejaculation, hormones, testicular function, or overall reproductive health. Infertility is common and affects both men and women; in many couples, male factors are involved either alone or alongside female factors, according to the World Health Organization and the CDC.

At a glance
What infertility causes means
Why infertility causes matter
Main causes of infertility
Male infertility causes
Female infertility causes
Shared and unexplained factors
Signs and symptoms
What is normal vs what is not
Tests used to look for infertility causes
What abnormal results can mean
Treatment options
How to improve fertility naturally
Questions to ask your doctor
Common myths
Related tests and terms
Frequently asked questions
References

At a glance

Infertility usually means not achieving pregnancy after 12 months of regular unprotected sex, or after 6 months if the female partner is 35 or older, as outlined by the American College of Obstetricians and Gynecologists.
Causes can come from the male partner, the female partner, both partners, or remain unexplained after testing.
Male infertility causes commonly include low sperm count, poor sperm movement, varicocele, hormone problems, testicular damage, genetic conditions, and blocked reproductive ducts.
Female infertility causes commonly include ovulation disorders, fallopian tube damage, endometriosis, uterine problems, and age-related decline in egg quantity and quality.
Lifestyle factors such as smoking, heavy alcohol use, obesity, anabolic steroid use, heat exposure, and certain medications can contribute.
A semen analysis is one of the most important first-line tests when evaluating male fertility, with reference ranges published by the WHO Laboratory Manual for the Examination and Processing of Human Semen.
Many causes are treatable or manageable, even when pregnancy does not happen quickly.
Because fertility problems can signal broader health issues, evaluation matters for overall health as well as conception.

What infertility causes means

The phrase infertility causes refers to the underlying reasons conception is delayed or does not occur. It is not a single disease. It is a broad term that covers many different issues that can affect the reproductive system.

In men, infertility causes may involve:

Too few sperm being produced
Sperm that do not swim well
Sperm with abnormal shape
Hormone imbalances that affect sperm production
Physical blockage preventing sperm from entering semen
Erectile dysfunction or ejaculation problems
Genetic or chromosomal disorders

In women, infertility causes may involve:

Irregular or absent ovulation
Blocked or damaged fallopian tubes
Endometriosis
Fibroids or uterine abnormalities
Diminished ovarian reserve
Age-related decline in egg quality

Sometimes testing finds more than one cause. In other cases, no clear reason is found despite a full workup; this is often called unexplained infertility.

Why infertility causes matter

Understanding infertility causes matters for three main reasons.

It guides treatment. A hormone issue is approached differently from a blocked tube or a varicocele.
It can uncover broader health conditions. Male infertility can sometimes be linked to hormonal disorders, genetic syndromes, metabolic disease, prior infections, or testicular problems. Reviews in Nature Reviews Urology and guidance from the American Urological Association note that a fertility evaluation can reveal important health information beyond reproduction.
It helps couples make better decisions. Depending on the cause, options may include timed intercourse, medication, surgery, intrauterine insemination (IUI), in vitro fertilization (IVF), or intracytoplasmic sperm injection (ICSI).

For many people, identifying the cause also reduces uncertainty. That can make the next steps feel more manageable.

Main causes of infertility

Infertility causes are often grouped into male factors, female factors, combined factors, and unexplained infertility.

Major categories

Male factor infertility: sperm, hormone, ejaculation, testicular, genetic, or structural issues
Female factor infertility: ovulation, egg reserve, tubal, uterine, cervical, or endometriosis-related issues
Combined infertility: both partners have contributing factors
Unexplained infertility: standard testing does not reveal a clear cause

According to the NICHD, infertility may result from one factor or several at the same time.

Comparison of common infertility causes

Male side: low sperm count, varicocele, low testosterone related hormone disruption, obstructive problems, sexual dysfunction, infection, genetic conditions
Female side: anovulation, polycystic ovary syndrome, endometriosis, tubal damage, diminished ovarian reserve, fibroids
Shared contributors: age, smoking, obesity, sexually transmitted infections, certain medications, environmental exposures

Male infertility causes

Male infertility causes account for a substantial share of fertility problems. The exact cause can range from something reversible to a chronic medical issue.

Sperm production problems

These are among the most common male infertility causes. They can show up as:

Oligozoospermia: low sperm concentration
Azoospermia: no sperm seen in the ejaculate
Asthenozoospermia: reduced sperm motility
Teratozoospermia: abnormal sperm morphology

These abnormalities may be related to testicular dysfunction, heat exposure, toxins, infection, genetic conditions, varicocele, or hormone problems. The WHO semen manual provides the standard framework for interpreting semen analysis findings.

Varicocele

A varicocele is an enlargement of veins in the scrotum. It is a common and potentially correctable male infertility cause. It may impair sperm production or function, possibly through increased scrotal temperature, oxidative stress, or altered blood flow. The AUA/ASRM male infertility guideline discusses varicocele evaluation and treatment.

Hormonal causes

Sperm production depends on healthy signaling between the brain and the testes. Disorders involving the hypothalamus, pituitary gland, or testes can disrupt this process.

Hypogonadotropic hypogonadism
Hyperprolactinemia
Thyroid disease
Severe testosterone suppression from anabolic steroid use
Primary testicular failure

Important point: low testosterone itself is not the same as infertility, but some causes of low testosterone affect fertility, and testosterone replacement therapy can suppress sperm production, as noted by the AUA guideline.

Obstruction or blockage

Sperm may be produced normally but blocked from reaching the ejaculate. Causes include:

Prior vasectomy
Congenital absence of the vas deferens
Scarring after infection or surgery
Ejaculatory duct obstruction

Congenital bilateral absence of the vas deferens is associated with CFTR gene mutations in many cases, a well-recognized link described in reproductive urology literature and summarized by the U.S. National Library of Medicine/MedlinePlus.

Genetic causes

Some men have infertility because of chromosomal or genetic conditions, including:

Klinefelter syndrome
Y chromosome microdeletions
CFTR-related conditions
Other rare gene variants affecting sperm production or transport

Genetic testing may be recommended in severe sperm count abnormalities or azoospermia.

Testicular damage

Undescended testicle
Testicular torsion history
Mumps orchitis
Chemotherapy or radiation
Trauma

Damage can impair sperm production permanently or temporarily, depending on the cause.

Sexual and ejaculation problems

Erectile dysfunction
Retrograde ejaculation
Delayed ejaculation
Anorgasmia
Difficulty having intercourse during the fertile window

These may be neurological, medication-related, vascular, hormonal, psychological, or mixed in origin.

Lifestyle and environmental contributors

Smoking
Heavy alcohol use
Obesity
Recreational drugs
Anabolic steroids
Heat exposure
Occupational chemical exposure
Poor sleep and chronic illness

Evidence suggests these can affect semen quality, though the effect size varies by person and exposure. The CDC/NIOSH discusses workplace and environmental reproductive risks.

Female infertility causes

Although this page is written with a men’s health audience in mind, infertility causes are often shared across a couple, so it is useful to understand common female factors too.

Ovulation disorders

If ovulation does not occur regularly, pregnancy becomes less likely. Common causes include:

Polycystic ovary syndrome (PCOS)
Hypothalamic amenorrhea
Thyroid disease
Hyperprolactinemia
Primary ovarian insufficiency

The NICHD lists ovulation problems among the most common female infertility causes.

Fallopian tube damage

Blocked or damaged tubes can prevent sperm and egg from meeting. Causes include pelvic inflammatory disease, prior surgery, endometriosis, or prior ectopic pregnancy.

Endometriosis

Endometriosis can affect fertility through inflammation, scar tissue, distortion of pelvic anatomy, and effects on egg or embryo implantation. The ACOG and NHS both describe its link with infertility.

Uterine or cervical factors

Fibroids that distort the uterine cavity
Uterine polyps
Congenital uterine anomalies
Scar tissue in the uterus
Cervical stenosis or cervical mucus issues

Age-related fertility decline

Female fertility declines with age because both egg quantity and egg quality decrease over time. This is one of the most important infertility causes at the population level. The ACOG provides patient guidance on age and fertility.

Shared and unexplained factors

Combined factors

It is common for both partners to have mild or moderate issues that together reduce the chance of pregnancy. For example, one partner may have slightly low sperm motility while the other has irregular ovulation.

Age

Age affects fertility in both sexes, although the effect is generally earlier and more pronounced in women. In men, advancing age may affect semen quality, DNA integrity, and time to conception, though many men remain fertile later in life.

Unexplained infertility

Unexplained infertility means standard testing does not identify a clear reason for the delay in conception. It does not mean nothing is wrong; it means current routine tests did not detect a specific cause. The American Society for Reproductive Medicine discusses unexplained infertility as a real and recognized diagnosis.

Timing and frequency

Sometimes the issue is not a disease but the timing of intercourse relative to ovulation. Conception is most likely when intercourse occurs during the fertile window in the days before ovulation and the day of ovulation.

Signs and symptoms

The main symptom of infertility is difficulty achieving pregnancy. Many people with infertility have no obvious symptoms at all. Still, some signs can point toward possible infertility causes.

Possible signs of male infertility causes

Low semen volume
Changes in sexual desire
Erectile or ejaculation problems
Testicular pain, swelling, or a history of undescended testes
Small testes
Breast enlargement
Reduced body hair or other signs of hormonal imbalance
Prior infertility, infections, surgery, chemotherapy, or anabolic steroid use

Possible signs of female infertility causes

Irregular or absent periods
Very painful periods
Pelvic pain
History of pelvic infection
Recurrent pregnancy loss
Signs of hormonal imbalance such as acne, excess hair growth, or galactorrhea

These symptoms do not confirm a diagnosis, but they can help guide testing.

What is normal vs what is not

There is no single “normal fertility test” that rules everything in or out. Still, some benchmarks are commonly used.

WHO lower reference limits for semen analysis

The World Health Organization provides reference limits from fertile populations. These numbers do not guarantee fertility or infertility, but they help interpret semen analysis results.

Semen volume: 1.4 mL or more
Sperm concentration: 16 million/mL or more
Total sperm number: 39 million per ejaculate or more
Total motility: 42% or more
Progressive motility: 30% or more
Normal morphology: 4% or more

Source: WHO Laboratory Manual for the Examination and Processing of Human Semen, 6th edition.

Normal vs concerning fertility findings

More reassuring: regular menstrual cycles, confirmed ovulation, open tubes, normal uterine cavity, semen parameters within reference ranges
Potentially concerning: no sperm in semen, very low sperm count, absent ovulation, blocked tubes, significant endometriosis, major uterine cavity distortion, severe pain, repeated pregnancy loss

Even when one result is abnormal, that does not always mean pregnancy is impossible. It means further interpretation is needed.

Tests used to look for infertility causes

Infertility testing should usually evaluate both partners. Starting with one person alone can miss an important part of the picture.

Common tests for male infertility causes

Medical history and physical exam
Includes puberty history, prior pregnancies, surgery, infections, medications, anabolic steroid use, heat exposure, and sexual function.
Semen analysis
The cornerstone test for male fertility evaluation. It measures semen volume, sperm concentration, motility, morphology, and related parameters.
Hormone testing
Common tests include FSH, LH, total testosterone, prolactin, and sometimes estradiol or thyroid studies.
Scrotal exam and sometimes ultrasound
Used when varicocele, masses, or structural issues are suspected.
Post-ejaculatory urinalysis
Can help evaluate retrograde ejaculation in selected cases.
Genetic testing
May include karyotype, Y chromosome microdeletion testing, or CFTR testing when indicated.

Common tests for female infertility causes

Ovulation assessment
Hormone tests
Ovarian reserve testing
Pelvic ultrasound
Hysterosalpingography to evaluate the tubes
Uterine cavity assessment

The ACOG and AUA/ASRM provide detailed guidance on fertility evaluation.

Testing overview table

Below is a simple comparison of common infertility tests and what they help detect.

Test	Who it is for	What it can show
Semen analysis	Male partner	Sperm count, motility, morphology, semen volume
Hormone panel	Both, depending on context	Endocrine causes affecting sperm production or ovulation
Scrotal ultrasound	Male partner	Varicocele, masses, structural abnormalities
Genetic testing	Male partner in selected cases	Chromosomal or gene-related infertility causes
Ovulation testing	Female partner	Whether ovulation is happening regularly
Hysterosalpingography	Female partner	Whether fallopian tubes are open
Pelvic ultrasound	Female partner	Fibroids, ovarian cysts, anatomic concerns

What abnormal results can mean

Abnormal fertility test results do not always point to one diagnosis, but they narrow the possibilities.

Examples from male fertility testing

Low volume semen: collection issue, low androgen status, ejaculatory duct obstruction, retrograde ejaculation
Low sperm concentration: testicular dysfunction, hormone issues, genetic factors, varicocele, toxins, medications
No sperm in semen: obstruction or severe sperm production failure
Low motility: infection, oxidative stress, varicocele, heat, lab variation, or idiopathic causes
Abnormal morphology: nonspecific finding that must be interpreted with the full semen profile
High FSH: may suggest impaired sperm production at the testicular level
Low testosterone with low or normal gonadotropins: may suggest secondary hypogonadism

Because semen parameters naturally vary, abnormal results are often repeated to confirm the pattern. The AUA/ASRM guideline emphasizes interpretation in clinical context rather than relying on one number alone.

Treatment options

Treatment depends on the cause, how long pregnancy has been delayed, the ages of the partners, and personal preferences.

Treatments for male infertility causes

Lifestyle changes: stopping smoking, limiting alcohol, avoiding anabolic steroids, weight management, treating sleep issues
Medical treatment: for selected hormone-related conditions or infections
Surgery: varicocele repair, sperm retrieval procedures, correction of obstruction in some cases
Assisted reproductive technology: IUI, IVF, or ICSI depending on semen quality and female factors

Treatments for female infertility causes

Ovulation induction medications
Surgery for selected cases of fibroids, polyps, or endometriosis
IUI
IVF

When assisted reproduction is considered

ART may be considered when there is severe male factor infertility, tubal disease, advanced maternal age, unexplained infertility not responding to simpler measures, or a need for sperm retrieval.

The CDC and ASRM offer patient-friendly information on reproductive treatments.

How to improve fertility naturally

Natural improvement is not a cure for every infertility cause, but evidence-based habits can support reproductive health.

Stop smoking.
Smoking is linked with poorer reproductive outcomes in both sexes.
Avoid anabolic steroids and non-prescribed testosterone.
These can sharply reduce sperm production.
Maintain a healthy weight.
Obesity can affect hormones, sperm quality, ovulation, and treatment success.
Limit heavy alcohol use and recreational drugs.
Review medications with a clinician.
Some drugs can affect fertility or ejaculation.
Reduce excessive heat exposure to the testes.
Examples include frequent hot tubs or prolonged high-heat occupational exposure.
Manage chronic conditions.
Diabetes, thyroid disease, sleep apnea, and other illnesses can indirectly affect fertility.
Time intercourse appropriately.
For many couples, regular intercourse every 1 to 2 days during the fertile window is reasonable.

Be cautious with supplements marketed as fertility boosters. Some may help specific deficiencies, but quality and evidence vary. It is better to use them under professional guidance than assume “natural” means effective or safe.

Questions to ask your doctor

What are the most likely infertility causes in our situation?
Should both partners be evaluated now?
Do I need a semen analysis, hormone testing, imaging, or genetic tests?
Could any of my medications, supplements, or past steroid use affect fertility?
Do my test results suggest a reversible problem?
How long should we try before moving to treatment?
Would lifestyle changes meaningfully improve our chances?
When should we consider IUI, IVF, or ICSI?
Could this fertility issue reflect a broader health problem?

Common myths

Myth: Infertility is usually a female problem

False. Male factors contribute to a large portion of infertility cases, which is why both partners should be evaluated.

Myth: If you can have sex, you cannot be infertile

False. Sexual function and fertility are related but not the same. A man can have normal erections and still have severe sperm abnormalities.

Myth: Testosterone therapy improves fertility

Often false. External testosterone commonly suppresses sperm production rather than improving it.

Myth: One abnormal semen analysis proves infertility

False. Semen values vary, and results must be interpreted in context, often with repeat testing.

Myth: Unexplained infertility means nothing is wrong

False. It means standard testing did not identify a clear cause, not that the problem is imaginary.

Semen analysis: lab test assessing sperm and semen parameters
Oligozoospermia: low sperm count
Azoospermia: no sperm in ejaculate
Asthenozoospermia: reduced sperm motility
Teratozoospermia: abnormal sperm morphology
Varicocele: enlarged scrotal veins associated with some cases of male infertility
FSH, LH, testosterone, prolactin: hormones often checked in fertility evaluation
IUI, IVF, ICSI: assisted reproductive treatments

Frequently asked questions

What is the most common cause of infertility?

There is no single most common cause overall. Infertility often results from ovulation problems, tubal disease, age-related decline, sperm abnormalities, varicocele, or a combination of factors.

What causes infertility in men most often?

Common male infertility causes include low sperm count, poor sperm motility, varicocele, hormone disorders, blockage, genetic conditions, prior testicular damage, and anabolic steroid use.

Can stress cause infertility?

Stress alone is not usually the sole cause, but it can affect sexual function, timing, hormone balance, and overall health. Fertility problems can also increase stress, so the relationship can go both ways.

Can infertility be cured?

Some causes are reversible or treatable, while others are managed rather than cured. Even when the underlying cause cannot be fully corrected, many couples still have options for building a family.

How long should you try before seeing a doctor?

In general, after 12 months of regular unprotected sex if the female partner is under 35, or after 6 months if she is 35 or older. Earlier evaluation makes sense if there are known risk factors, irregular periods, prior cancer treatment, testicular problems, or no sperm on prior testing.

Can you be infertile and still have normal sexual performance?

Yes. Fertility depends on more than erections or libido. Many men with infertility have normal sexual function.

Does a low sperm count mean pregnancy is impossible?

No. A low sperm count lowers the chance of conception but does not automatically rule it out. The degree of reduction and other factors matter.

Can testosterone lower fertility?

Yes. Testosterone replacement therapy and anabolic steroids can suppress the hormonal signals needed for sperm production.

What if all the tests are normal but pregnancy still is not happening?

That situation may be labeled unexplained infertility. It is still a recognized clinical problem, and treatment options may include expectant management, IUI, or IVF depending on age and timing.