A Decade of Semen Quality Trends in Libya: Nonlinear Temporal Patterns, Age Effects, and WHO 2010–2021 Reclassification

Abstract Reports of declining sperm concentration, count, and motility remain contested amid methodological heterogeneity, geographic bias, and reference-limit changes, and data from the Middle East and North Africa are scarce. We conducted a retrospective single-center cohort study of 3,078 men undergoing first diagnostic semen analysis at the National Fertility Teaching Center, Eastern Libya, between 2016 and 2025/26, with stable personnel, equipment, and protocols. Multivariable regression adjusted for age and semen volume assessed temporal trends, using restricted cubic splines for nonlinearity, robust sensitivity analyses, and Benjamini-Hochberg correction; samples were classified under both WHO 2010 and WHO 2021 reference limits. Calendar year showed small but statistically significant associations with semen volume (−0.028 mL/year, p=0.005), normal morphology (−1.7%/year, p=0.012), and total motility (+0.43 percentage points/year, p=0.014); declines in sperm concentration and total sperm count were directionally similar but non-significant after correction, and effect sizes were modest throughout (adjusted R2 ≤ 0.033). All five non-volume parameters followed a nonlinear trajectory, peaking around 2019–2020, declining through 2022–2023, and partially recovering; the decline appeared more pronounced in men under 45 years, with older men comparatively stable — an exploratory finding discussed further below. Applying WHO 2021 criteria reduced asthenozoospermia prevalence from 53.8% to 48.6% and increased oligozoospermia prevalence from 35.7% to 37.0%. In this Eastern Libyan clinical population, semen parameters changed modestly and nonlinearly rather than declining uniformly, with age-specific divergence and measurable WHO-reclassification; findings should not be generalized to Libyan men overall but offer novel data from an underrepresented population and support continued surveillance and multicenter collaboration. Lay Summary This study investigated trends in male fertility by analyzing semen data from 3,078 men in Libya over a ten-year period (2016–2026). The researchers evaluated essential factors, including sperm count, movement, and shape. The findings revealed that sperm quality did not experience a straightforward decline, but rather fluctuated unevenly over the decade. Furthermore, the data confirmed that older age is steadily linked to lower sperm quality. Finally, the study demonstrated that switching from older medical criteria to the updated 2021 World Health Organization guidelines changes how many men are classified as having fertility issues. These results highlight the critical need for clinics to adopt the latest global diagnostic standards, ensuring more accurate fertility assessments and better-tailored patient care.