Trend of change of sperm count and concentration over the last two decades: A systematic review and meta‐regression analysis

Background: Since the 1970s, several studies found that sperm concentration (SC) and total sperm count (TSC) constantly worsened over time, mainly in high-income countries. Objectives: To evaluate whether the decreasing trend in sperm count is continuing in Western European countries and USA, we performed a systematic review and meta-regression analysis. Materials and methods: Embase and Pubmed/Medline were searched papers published in English in the 2000-2020 period limiting the search to data collected in the USA and Western European countries. Results: We identified 62 articles and pooled information on 24,196 men (range 10-2,523), collected from 1993 to 2018. Considering all the studies, random-effects meta-regression analyses showed no significant trend for SC (slope per year -0.07 mil/mL, p-value = 0.86). Negative trends of SC were detected in Scandinavian countries (slope per year -1.11 mil/mL, 95% CI: -2.40 to +0.19; p-value = 0.09), but the findings were statistically not significant. No significant trends of SC were detected in Central Europe (slope per year +0.23, 95% CI -2.51 to +2.96; p-value = 0.87), the USA (slope per year +1.08, 95% CI -0.42 to +2.57; p-value = 0.16), and Southern Europe (slope per year +0.19, 95% CI -0.99 to +1.37; p-value = 0.75). We have analyzed separately findings from studies including sperm donors, fertile men, young unselected men (unselected men, study mean age < 25 years) and unselected men (unselected men, study mean age ≥ 25 years). No significant trends of SC were observed among sperm donors (slope per year -2.80, 95% CI -6.76 to +1.17; p-value 0.16), unselected men (slope per year -0.23, 95% CI -1.58 to +1.12; p-value 0.73), young unselected men (slope per year -0.49, 95% CI -1.76 to +0.79; p-value 0.45), fertile men (slope per year +0.29, 95% CI -1.09 to +1.67; p-value 0.68). Discussion and conclusion: The results of this analysis show no significant trends in SC, in USA, and selected Western European countries.