Many men assume their fertility remains steady—but modern studies show otherwise. By the mid-30s, sperm count, motility and genetic integrity begin to decline, and by age 40 fertility can fall by as much as 50 per cent. In this article, we explain the biological mechanisms, summarise key research findings and outline when a urological assessment is recommended.
Biology of Sperm Production as Men Age
Spermatogenesis begins at puberty and, in theory, continues throughout life. In the 20s and early 30s, the body produces the greatest number of high-quality sperm. After around 40 years, sperm count may decrease by up to 50 per cent from its peak, motility declines by approximately 0.17–0.6 per cent per year, and morphology deteriorates due to lower testosterone levels and oxidative stress (WHO 2020).
Age-Related Declines in Count and Quality
- Lower sperm count: Fewer sperm reduce the probability of fertilisation.
- Reduced motility: Slower sperm are less likely to reach the egg.
- Altered morphology: Changes in shape and structure hinder penetration of the egg.
A review by the National Institutes of Health found that DNA fragmentation rises significantly after age 40, increasing the risk of miscarriage (NIH 2015).
Clinical Reference Values for Semen Parameters
- 15–200 million sperm/mL is considered the normal concentration range by the WHO 2018.
- Over 39 million sperm per ejaculate is optimal for natural conception.
Persistent values below these thresholds warrant a medical assessment, especially when planning a family.
Key Statistics and Study Findings
- Motility decline: A reduction of 3–12 per cent over 20 years documented in cohort studies (NIH 2010).
- Epigenetic markers: Age-related DNA methylation changes confirmed in large-scale research (PubMed 2019).
- Preterm births & birth weight: Fathers aged 45+ have 21 per cent more preterm births and 24 per cent more low-birth-weight infants (PubMed 2018).
- Neuropsychiatric risks: Slightly higher rates of autism and schizophrenia in children of older fathers (PubMed 2013).
Testosterone Decline and Andropause
Total testosterone falls by about 0.8 per cent per year and free testosterone by around 2 per cent. This decline can contribute to reduced libido, lower ejaculate volume and slower sperm maturation (PubMed 2004).
Genetic Risks with Advancing Age
As men age, DNA fragmentation and chromosomal abnormalities become more common, increasing miscarriage risk and potential genetic disorders (PubMed 2006).
Impact on Offspring
Paternal age affects not only conception but also outcomes such as preterm birth rates, low birth weight and minor neuropsychiatric risks in children (PubMed 2013).
When to Seek Medical Advice
The WHO 2018 advises that couples consult a urologist after 12 months of unprotected intercourse without pregnancy. For women aged 35 and over, evaluation after 6 months is recommended, and immediate assessment is needed if risk factors such as testicular inflammation or injury are present.
Conclusion
Age impacts male fertility in many ways—from hormonal changes and genetic risks to measurable declines in sperm count and motility. Understanding your fertility parameters and seeking timely medical assessment can greatly improve your chances of successful family planning.