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Condition

Teratozoospermia (Abnormal Sperm Morphology)

Teratozoospermia is a semen-analysis finding in which a lower-than-expected proportion of sperm have normal shape and structure. Abnormal sperm morphology can involve the head, midpiece, or tail and may be associated with reduced fertility potential, although morphology alone cannot determine whether a man is fertile or infertile.

Also known as: Abnormal sperm morphology, Poor sperm morphology, Low sperm morphology, Abnormally shaped sperm, Sperm morphology problems, Teratospermia, Teratozoospermia, Low normal forms, Abnormal sperm shape, Poor sperm shape

Symptoms9 listed
ICD-10N46.9
TreatableYes
DE
Medically reviewed by Dr. Elif Yılmaz, MD, FECSM
Last reviewed 23 August 2026
✓ Clinician reviewed
Teratozoospermia✓ Clinician-reviewed information
Key takeaways
  • Teratozoospermia means a lower-than-expected percentage of sperm have normal morphology on semen analysis.
  • Sperm morphology evaluates the structure of the sperm head, midpiece, and tail.
  • Abnormal morphology may occur alone or together with low sperm count and poor sperm motility.
  • A low morphology percentage does not by itself mean that natural conception is impossible.
  • Evaluation focuses on the complete semen analysis, reproductive history, potentially treatable causes, and fertility factors affecting both partners.

Overview

Teratozoospermia refers to an increased proportion of sperm with abnormal morphology.

Morphology describes the physical shape and structure of sperm when examined under a microscope.

A normally formed sperm has several important components:

  • Head

  • Acrosome

  • Midpiece

  • Tail

Abnormalities can affect one or several of these structures.

Laboratories assess sperm morphology using standardized criteria and report the percentage of sperm classified as morphologically normal.

A low percentage of normal forms may be described as teratozoospermia.

What does abnormal sperm morphology look like?

Morphological abnormalities can involve different parts of the sperm.

Head abnormalities

Examples include:

  • Large heads

  • Small heads

  • Tapered heads

  • Irregular heads

  • Round heads

  • Multiple heads

  • Abnormal acrosomes

  • Vacuolated heads

Midpiece abnormalities

Examples include:

  • Thick midpieces

  • Bent midpieces

  • Irregular midpieces

  • Abnormal attachment of the midpiece to the head

Tail abnormalities

Examples include:

  • Short tails

  • Bent tails

  • Coiled tails

  • Irregular tails

  • Multiple tails

Many semen samples contain some abnormally shaped sperm. The important measurement is the proportion meeting standardized normal morphology criteria.

What does 4% normal morphology mean?

Under strict morphology assessment, the WHO Sixth Edition reports a lower fifth-centile reference value of approximately 4% normal forms in the reference population of fertile men.

This number is often misunderstood.

It does not mean that:

  • 96% of the sperm are necessarily incapable of fertilization.

  • A man with 3% morphology is infertile.

  • A man with 5% morphology is automatically fertile.

Semen reference values describe distributions observed in fertile populations and are not absolute diagnostic boundaries between fertility and infertility.

Morphology should therefore be interpreted together with sperm concentration, motility, total sperm number, reproductive history, and female-partner factors.

Is teratozoospermia the same as infertility?

No.

Teratozoospermia can be associated with reduced fertility potential, particularly when severe or combined with other semen abnormalities.

However, morphology alone has limited ability to predict whether an individual couple will conceive naturally.

Some men with very low percentages of normal forms achieve natural pregnancies.

Conversely, a normal morphology result does not guarantee fertility.

What is OAT syndrome?

When three major sperm abnormalities occur together, the condition is often called oligoasthenoteratozoospermia (OAT).

This means:

  • Oligozoospermia: low sperm concentration

  • Asthenozoospermia: reduced sperm motility

  • Teratozoospermia: abnormal sperm morphology

OAT can represent more substantial impairment of spermatogenesis than an isolated abnormality and generally warrants comprehensive male infertility evaluation.

Types of teratozoospermia (abnormal sperm morphology)

Isolated Teratozoospermia
Morphology is abnormal while sperm concentration and motility are otherwise relatively preserved. The effect of isolated teratozoospermia on fertility remains less predictable than when several semen parameters are abnormal.
Severe Teratozoospermia
Only a very small percentage of sperm meet normal morphological criteria. Severe abnormalities should be interpreted in the context of the entire semen analysis rather than morphology alone.
Oligoasthenoteratozoospermia (OAT)
Low sperm concentration, reduced motility, and abnormal morphology occur together. OAT may indicate broader impairment of testicular sperm production and deserves comprehensive evaluation.
Globozoospermia
Globozoospermia is a rare, specific sperm morphology disorder characterized by round-headed sperm lacking a normal acrosome. It can severely impair fertilization and is associated with genetic abnormalities in some patients.
Macrozoospermia
Macrozoospermia is a rare severe sperm morphology disorder characterized by abnormally large sperm heads, often with multiple tails. Some cases are associated with AURKC gene variants and high rates of chromosomal abnormalities.
How common is it?
Abnormal sperm morphology is frequently identified during male infertility evaluation, but the prevalence of isolated teratozoospermia varies widely according to the population studied, laboratory technique, and morphology criteria used. There is therefore no single reliable prevalence percentage for the general male population.
Source: who.int

Symptoms

Difficulty conceiving
Abnormal sperm morphology on semen analysis
Low percentage of normal sperm forms
Repeated abnormal semen analyses
Low sperm concentration in combined cases
Reduced sperm motility in combined cases
Oligoasthenoteratozoospermia
Varicocele in some men
History of testicular or reproductive disease

Causes

Varicocele
Testicular dysfunction
Genetic abnormalities
Oxidative stress
Genital tract infection or inflammation
Recent fever or systemic illness
Smoking
Obesity
Excessive heat exposure
Environmental or occupational toxins
Testicular injury
Previous chemotherapy
Some medications or medical treatments
Hormonal abnormalities in selected patients
Genetic sperm-head or flagellar disorders
Abnormal spermatogenesis
Idiopathic causes where no specific cause is identified

Risk factors

Varicocele
Smoking
Obesity
Metabolic disease
Excessive testicular heat exposure
Occupational toxin exposure
Previous testicular injury
Previous chemotherapy or radiotherapy
Genital tract infection or inflammation
Genetic reproductive disorders
Recent high fever
Other abnormal semen parameters
Testicular dysfunction
Increasing paternal age may influence some sperm-quality measures

How it is diagnosed

Teratozoospermia is identified through semen analysis with sperm morphology assessment.

Semen analysis

A semen analysis evaluates several parameters, including:

  • Semen volume

  • Sperm concentration

  • Total sperm number

  • Progressive motility

  • Total motility

  • Sperm morphology

  • Vitality when indicated

Morphology should not be interpreted independently from the other findings.

Sperm morphology assessment

A laboratory prepares and stains a semen sample so individual sperm can be examined microscopically.

The embryologist or laboratory professional evaluates the:

  • Head

  • Acrosomal region

  • Midpiece

  • Tail

  • Overall proportions of the sperm

Strict criteria are used to determine which sperm meet the definition of a normal form.

Repeat semen analysis

Semen parameters naturally vary.

An abnormal result may therefore be repeated, particularly when it could influence major fertility decisions.

Factors that may temporarily alter semen quality include:

  • Fever

  • Recent illness

  • Abstinence duration

  • Medications

  • Sample collection problems

  • Laboratory variability

Male fertility assessment

Persistent abnormal morphology may prompt evaluation of:

  • Fertility history

  • Previous pregnancies

  • Duration of infertility

  • Testicular development

  • Varicocele

  • Genital infections

  • Testicular trauma

  • Previous surgery

  • Medications

  • Smoking

  • Heat exposure

  • Occupational exposures

  • Anabolic steroid or testosterone use

Hormonal testing

Hormonal testing may be appropriate when abnormal morphology occurs together with low sperm concentration or other evidence of impaired testicular function.

Potential tests include:

  • FSH

  • LH

  • Total testosterone

  • Prolactin when indicated

Genetic testing

Routine genetic testing is not required simply because morphology is below the reference range.

However, genetic testing becomes particularly important when a characteristic severe monomorphic abnormality is present.

Examples include:

  • Globozoospermia

  • Macrozoospermia

  • Severe flagellar abnormalities

These patterns can be associated with specific genetic disorders and may have important implications for assisted reproduction.

When to see a doctor
  • A semen analysis shows very low normal sperm morphology.
  • Abnormal morphology persists on repeat testing.
  • You and your partner have difficulty conceiving.
  • Low morphology occurs together with low sperm count or poor motility.
  • Your report shows oligoasthenoteratozoospermia.
  • The laboratory reports a specific abnormal pattern such as globozoospermia.
  • You have a varicocele and abnormal semen parameters.
  • You have previously received chemotherapy or radiotherapy.
  • You have used anabolic steroids or testosterone.
  • You want to understand whether natural conception, IUI, IVF, or ICSI is appropriate.
Reducing your risk
  • Stop smoking.
  • Maintain a healthy body weight.
  • Exercise regularly.
  • Avoid anabolic steroid misuse.
  • Avoid unnecessary testosterone therapy when fertility is desired.
  • Reduce excessive testicular heat exposure.
  • Use workplace protection around reproductive toxins.
  • Seek appropriate treatment for genital infections.
  • Manage diabetes and metabolic disease.
  • Avoid excessive alcohol consumption.
  • Discuss fertility-toxic medications with a doctor.
  • Seek evaluation for clinically significant varicocele when infertility is present.
  • Maintain balanced nutrition.

Common questions

What is teratozoospermia?
Teratozoospermia means a lower-than-expected proportion of sperm meet normal morphological criteria during semen analysis.
What does sperm morphology mean?
Sperm morphology describes sperm shape and structure, including the head, acrosome, midpiece, and tail.
What is normal sperm morphology?
Laboratories commonly use strict criteria. The WHO Sixth Edition reports approximately 4% normal forms as the lower fifth-centile value in its fertile reference population, but this should not be interpreted as a strict fertile-versus-infertile cutoff.
Is 3% sperm morphology bad?
A result of 3% is below the commonly cited lower reference value, but it does not by itself establish infertility. The complete semen analysis and the couple's reproductive circumstances are more important than a single morphology percentage.
Can you get pregnant naturally with low sperm morphology?
Yes. Natural pregnancies can occur in couples where the male partner has low sperm morphology, particularly when sperm concentration and motility are otherwise favorable.
Does abnormal sperm shape mean abnormal DNA?
Not necessarily. Morphology and sperm DNA integrity are different characteristics. Abnormal morphology does not automatically mean that every abnormally shaped sperm has damaged DNA.
Can teratozoospermia improve?
Sometimes. Improvement depends on the cause. Treatable contributors such as varicocele or certain exposures may be addressed, while genetic morphology disorders may persist.
Can varicocele cause abnormal sperm morphology?
Varicocele is associated with impaired semen parameters in some infertile men, which can include morphology abnormalities.
Can smoking affect sperm morphology?
Smoking is associated with poorer semen quality and oxidative stress and may adversely affect several aspects of sperm function.
Does abnormal morphology cause miscarriage?
Male reproductive factors, including sperm DNA damage in selected circumstances, may influence reproductive outcomes, but a low morphology percentage alone should not be assumed to be the cause of miscarriage.
Do supplements improve sperm morphology?
Antioxidants and fertility supplements are widely marketed, but evidence that they improve clinically meaningful outcomes such as pregnancy or live birth is inconsistent. They should not replace evaluation for an underlying cause.
Can IUI work with teratozoospermia?
IUI may be considered in selected couples depending on total motile sperm count, the severity of the male factor, female fertility factors, and duration of infertility. Morphology alone should not determine the decision.
Can IVF treat teratozoospermia?
IVF may be appropriate when significant male-factor infertility or additional fertility factors are present.
When is ICSI used for abnormal sperm morphology?
ICSI may be considered in severe male-factor infertility, previous fertilization failure, certain severe morphology disorders, or other appropriate reproductive circumstances. Isolated low morphology alone does not automatically mean every couple requires ICSI.
What is globozoospermia?
Globozoospermia is a rare severe sperm disorder in which sperm have round heads and lack a normal acrosome. It can severely impair the sperm's ability to fertilize an egg.
What is macrozoospermia?
Macrozoospermia is a rare genetic sperm disorder characterized by very large abnormal sperm heads and frequently multiple flagella. It can be associated with AURKC gene variants and significant chromosomal abnormalities.
What is OAT syndrome?
Oligoasthenoteratozoospermia means low sperm concentration, poor sperm motility, and abnormal sperm morphology occur together.
Which doctor treats teratozoospermia?
An andrologist or reproductive urologist can evaluate abnormal sperm morphology, investigate associated male infertility factors, and determine whether a treatable cause is present.

Sources

  1. WHO Laboratory Manual for the Examination and Processing of Human Semen, Sixth Edition https://www.who.int/publications/i/item/9789240030787
  2. EAU Guidelines on Sexual and Reproductive Health — Male Infertility https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-infertility
  3. Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline https://www.auanet.org/guidelines-and-quality/guidelines/male-infertility