Background

Previous meta-analyses concluded that there is a decline in sperm parameters over time. This conclusion might be incorrect due to inherent biases or focusing only on a single parameter – sperm concentration.

Objective

To study trends in sperm parameters over the past twenty years using data from the trials that defined the reference ranges of the World Health Organization manual.

Materials and methods

Retrospective evaluation of the data used to define the World Health Organization reference ranges. The data from 11 studies, including 3589 participants between 1996–2016, were divided into three period groups based on the decade of study. Differences in semen parameters’ distribution were presented in boxplot. P-values were calculated by the Kruskal Wallis rank-sum test followed by Dunn post-hoc test. Analyses were conducted using the R programming language.

Results

A small decrease was noted in mean sperm concentrations (88.1 million/ml, 87.6 million/ml and 77.2 million/ml for the first second and third decades respectively) (p<0.01). However, the 5th percentile of sperm concentration for the third decade was higher than the first or second decades (18 million/ml vs. 14.9 million/ml and 15 million/ml respectively). No significant differences were noted in progressive motility over the years (p = 0.32). The percent of morphologically normal sperm decreased between the first (24.2%) and the second (12.6%) periods of the study (p<0.001) and then increased in the third decade (14.2%) (p<0.01). While TMC declined between the second and third decades (189 million and 153.9 million respectively, p<0.001), at levels unlikely to decrease fertility. However, the 5th percentile of the TMC remained stable at 24.9, 20.8 and 20.6 million, for the first, second and third decades respectively (p = 0.36).

Discussion and Conclusion and relevance

Trends in sperm parameters over the last three decades do not seem to be clinically significant.

This article is protected by copyright. All rights reserved