Trends in male semen parameters (2011–2018): a large-scale retrospective analysis of 5,886 cases based on the fifth edition WHO manual

Importance Global reports suggest declining sperm quality, but data from Asian populations under standardized conditions are limited. Investigating trends in China is critical for understanding modifiable factors affecting male fertility. Objective To assess decade-long trends in semen quality among healthy Chinese men and evaluate associations with environmental factors. Design, Setting, and Participants: Retrospective cohort analysis of 5,886 semen samples from healthy sperm donors (aged 20–45 years) recruited between 2011 and 2018 at the Beijing Human Sperm Bank. All procedures adhered strictly to WHO 5th Edition laboratory standards. Main Outcomes and Measures: Annual trends in semen volume, sperm concentration (SC), total sperm count (TSC), progressive motility (PR), total motility (PR + NP), and percentage of progressive motility (PPR). Associations between semen parameters and environmental pollutants (SO₂, NO₂, PM10, PM2.5, waterborne PI/AN) were evaluated using Spearman correlation. Results From 2011 to 2018, significant improvements occurred across key parameters: SC increased by 12.3% (78–96.5 × 10 6 /mL; p 0.05 in 2013, 2018); TSC increased by 18.7% (200–283.5 × 10 6 /ejaculate; p 0.05 from 2014 to 2017); PR and PPR also significantly improved ( p 0.05 in multiple years). Negative correlations were observed between pollutants and semen quality: SO₂, NO₂, and PM10 inversely correlated with TSC ( ρ = −0.719 to −0.929; p ≤ 0.045) and PPR ( ρ = −0.826 to −0.922; p ≤ 0.011). Water pollutants (PI, AN) similarly correlated with reduced semen volume, TSC, and motility ( ρ = −0.735 to −0.878; p ≤ 0.038). Conclusions and relevance Contrary to global declines, semen quality significantly improved among healthy Beijing donors from 2011 to 2018. This improvement coincided with aggressive environmental policies (e.g., China’s 2013–2017 Air Pollution Action Plan), suggesting pollution-related sperm damage may be reversible with targeted interventions.