How Is Semen Quality Assessed Beyond Conventional Semen Analysis?
Semen quality is a global health concern. Over recent decades, a worldwide decline in semen quality has been observed, with important implications for male fertility. This trend has led the World Health Organization (WHO) to revise the standards used to evaluate human semen after significant decreases in sperm concentration and motility were identified. In fact, sperm concentration is estimated to have declined by approximately 50% since 1973.
When a couple experiences difficulties achieving pregnancy, the fertility assessment should investigate both female and male factors. In men, the first test usually performed is a semen analysis (seminogram), which evaluates the basic characteristics of semen and serves as the starting point for the assessment of male fertility.
Parameters That Define Semen Quality (Concentration, Motility and Morphology)
The parameters evaluated during a semen analysis include sperm concentration, motility, morphology and vitality. Results are interpreted according to the WHO reference values published in the 6th edition of the WHO Laboratory Manual for the Examination and Processing of Human Semen, released in July 2021.
One of the main changes introduced in this edition is the replacement of the concept of “normal values” with decision limits, based on the fifth percentile of a population of fertile men. These values do not establish a threshold between fertility and infertility but rather indicate probabilities that should always be interpreted individually for each patient.
WHO 2021 Reference Values
The WHO 2021 decision limits (5th percentile) for the main semen parameters are as follows:
| Parameter | Decision Limit (5th Percentile) |
|---|---|
| Semen volume | ≥ 1.4 ml |
| Sperm concentration | ≥ 16 million/ml |
| Total sperm count | ≥ 39 million per ejaculate |
| Total motility | 42% |
| Progressive motility | 30% |
| Normal morphology | 4% |
| Vitality | 54% |
Beyond the Semen Analysis: Advanced Techniques for Assessing Semen Quality
Although semen analysis is the first-line test for evaluating male fertility, it does not always identify the underlying cause of infertility. Some men with normal semen analysis results experience difficulties conceiving, while others with altered parameters are able to achieve pregnancy. For this reason, fertility specialists often rely on complementary molecular and genetic tests to provide a more accurate diagnosis and tailor treatment to each patient.
Among the most relevant complementary tests is sperm DNA fragmentation analysis, which identifies sperm carrying DNA strand breaks. Increased DNA fragmentation has been associated with reduced fertilisation potential, poorer embryo quality and a higher risk of miscarriage.
Another important technique is fluorescence in situ hybridisation (FISH). This cytogenetic test evaluates part of the chromosomal complement of sperm cells, specifically chromosomes 13, 18, 21, X and Y, which are mainly associated with miscarriage and foetal chromosomal abnormalities.
More recently, next-generation sequencing (NGS) has become a key tool in male fertility by enabling the simultaneous analysis of multiple genes involved in spermatogenesis through dedicated genetic panels. These panels assess, within a single test, the genes most closely associated with the formation of male gametes. Their use in patients with abnormal semen analysis results improves diagnostic accuracy and supports a more personalised approach to reproductive medicine.
Sperm Selection Techniques
In assisted reproduction, assessing semen quality is only one part of the process. Equally important is selecting the sperm cells with the greatest fertilising potential.
Several sperm selection techniques have been developed to isolate sperm with the best functional characteristics before certain assisted reproductive treatments are performed. These include the granulosa cell selection dish (developed by Instituto Bernabeu), microfluidic systems, MACS and PICSI, among others.
The choice of technique depends on each patient’s clinical characteristics and the specific medical indication, allowing treatment to be individualised while maximising the chances of success.
Factors Affecting Semen Quality
Several factors may contribute to the deterioration of semen parameters, including genetic abnormalities, hormonal imbalances and a range of testicular disorders.
In addition, lifestyle habits and exposure to environmental factors have also been identified as potential contributors, although the scientific evidence supporting their impact is less conclusive.
Factors Affecting Semen Quality
Several factors may contribute to the deterioration of semen parameters, including genetic abnormalities, hormonal imbalances and a range of testicular disorders.
In addition, lifestyle habits and exposure to environmental factors have also been identified as potential contributors, although the scientific evidence supporting their impact is less conclusive.
Diet and Lifestyle
Obesity and diets high in ultra-processed foods disrupt hormonal balance by reducing testosterone levels and promoting inflammation and oxidative stress. As a result, sperm concentration, motility and morphology may deteriorate, while DNA damage may increase.
Smoking, electronic cigarettes (vaping), excessive alcohol consumption, anabolic steroids, cannabis and opioids can all impair spermatogenesis and reduce semen quality.
Stress and Environmental Factors
Environmental pollution, pesticides, heavy metals and endocrine-disrupting chemicals (such as bisphenols and phthalates) have been linked to reproductive toxicity and may reduce sperm concentration while increasing DNA damage.
In addition, increased scrotal temperature—caused by frequent sauna use, tight-fitting clothing or occupational heat exposure—may negatively affect semen parameters such as sperm motility.
Chronic stress may disrupt hormonal regulation and increase oxidative damage. Furthermore, although sperm production is maintained throughout life, advanced paternal age may increase the risk of genetic abnormalities in sperm cells.
Medical Conditions and Disorders
A range of medical conditions may have a negative impact on semen quality.
Although many medications are essential for treating specific health conditions, some may produce side effects that can affect male fertility and semen quality. These include anabolic steroids, chemotherapy drugs, psychotropic medications, finasteride and dutasteride, among others.
Actions to Improve Semen Quality
Current scientific evidence suggests that the most effective strategy for improving sperm quality naturally is to adopt a healthy lifestyle. Weight loss (particularly in men who are overweight or obese), smoking cessation, reducing alcohol and recreational drug use, and minimising exposure to environmental toxins may help improve certain semen parameters.
In addition to these lifestyle measures, other strategies have been proposed to improve male reproductive function, including antioxidant supplementation. Although promising results have been reported in some cases, the available scientific evidence remains insufficient to recommend their routine use.
Ultimately, the primary goal extends beyond improving semen analysis results. The objective is to increase the likelihood of achieving a successful pregnancy and the birth of a healthy baby, whether through natural conception or, when indicated, assisted reproductive techniques.
Frequently Asked Questions
How can I tell if I have good-quality sperm?
The most reliable way to determine whether sperm quality is poor or whether semen parameters fall within the WHO reference values is to undergo a semen analysis. This test evaluates sperm concentration, motility, morphology and other key characteristics of semen.
However, a normal semen analysis does not always rule out conditions that may affect male fertility. If a couple experiences difficulty conceiving, recurrent miscarriage or results that require a more comprehensive assessment, the fertility specialist may recommend additional tests to evaluate aspects that cannot be detected through a conventional semen analysis.
For this reason, semen analysis results should always be interpreted by a specialist with expertise in male fertility, who will determine whether further diagnostic testing is required.
Are supplements effective for improving sperm quality?
In recent years, the use of antioxidants and vitamin supplements to improve sperm quality has become increasingly popular. However, the available scientific evidence indicates that there is still insufficient proof of their effectiveness to recommend their routine use.
Are there foods that improve semen quality?
A balanced diet, together with healthy lifestyle habits—including regular physical activity, maintaining a healthy weight, and avoiding smoking and excessive alcohol consumption—may contribute to overall health and support certain semen parameters.
However, no specific food has been shown to improve fertility on its own. Current scientific evidence therefore emphasises that maintaining good overall health is the most important strategy, and that men experiencing difficulties conceiving should seek advice from a fertility specialist.
What are the requirements for becoming a sperm donor?
Becoming a sperm donor requires passing a comprehensive medical and semen assessment to ensure that the sample meets the standards established by current legislation and the centre’s quality protocols.
Among other evaluations, semen parameters, general health (including psychological assessment), and the donor’s personal and family medical history are carefully assessed.
If you would like to learn more about the eligibility criteria and the complete donation process, please visit our Sperm Donation information page.
Dr Eva García, Biologist at Instituto Bernabeu.