Seminal profile of 23,504 patients over the years: 7 years of experience

Spatiotemporal trends in human semen quality

Over the past four decades, studies of various designs have reported spatial and temporal trends in human semen quality. Several standardized-methodology studies in homogeneous populations that compare specific cities within a country or a continent provide clear evidence of geographical differences in sperm production, even over short distances within the same country. Human sperm production is widely believed to be declining over time, but evidence from the scientific literature is less clear. Studies based on repeated cross-sectional data from a single centre have shown mixed results. Among the numerous retrospective studies conducted in a single centre, only some included homogeneous groups of men and appropriate methods, and most of them suggest a temporal decrease in human sperm production in the geographical areas considered. Conclusions reporting temporal trends in sperm production that came from existing retrospective multicentre studies based on individual semen data and those using means, medians or estimates of sperm production are questionable, owing to intrinsic limitations in the studies performed. Regardless of study design, studies on the percentage of motile or morphologically normal spermatozoa are still limited by the inherent variability in assessment. Overall, available data do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world, but that a trend is observed in some specific areas. To understand these trends and contrasts in sperm and semen quality, prospective studies should be encouraged and combined with assessment of the male exposome.

Several studies over the past few decades have suggested that sperm quality varies by geographical region and might be subject to a temporal decline worldwide. However, the data supporting these conclusions have come from studies of various methodologies and heterogeneous populations, making them unreliable. In this in-depth Review, Chevrier and colleagues discuss the data surrounding discussion of spatiotemporal trends in semen parameters and consider how these trends and the factors promoting them interact.

The vast literature on human semen quality trends is extremely heterogeneous in terms of the populations studied and study designs, and so these studies have been unable to draw firm conclusions.

Understanding the data around spatiotemporal semen trends requires a focus on the methodological choices and application of criteria to filter findings from the studies with optimal design.

Numerous appropriately designed studies suggest unambiguous geographical contrasts in human sperm production; however, evidence of a decline in sperm production is reliable only in specific populations and cities in which studies with a complete set of quality criteria have been conducted.

By contrast, suggestions of a worldwide drop in human semen quality on the basis of retrospective multicentre studies cannot be substantiated, owing to intrinsic limitations in the studies performed.

Many and varied factors of variation, in particular the diverse modalities of assessment, do not enable us to conclude that clear temporal trends of sperm motility and normal morphology are present.

Progress in our understanding of the highlighted trends and their causal factors requires prospective studies that minimize all known biases combined with the assessment of men’s exposome.

Hope for male fecundity: clinically insignificant changes in semen parameters over 10 years at a single clinic while assessing an infertility population

PURPOSE

What is the trend in sperm parameters in a group of men attending a single reproductive center, over a 10-year period?

METHODS

A retrospective study was conducted on 12,188 semen samples obtained from unique individuals who attended a university reproductive clinic from 2009 to 2018, inclusively. Semen analysis was done using computer-assisted sperm analysis and verified by an andrologist. Analysis was done after dividing the dataset into two groups: above WHO 2010 lower reference limits (ARL) (N = 6325) and below the reference limits (BRL) (N = 5521).

RESULTS

Volume increased slightly (ARL, p = 0.049) before returning to baseline or was stable (BRL, p = 0.59). Sperm concentration and total count of the BRL and ARL group declined initially and then recovered slightly (p < 0.0001, in all cases). Although these changes were statistically significant, this was due to the large study population; clinically, these changes were quite mild and would not have been significant for fertility. Sperm total motility and progressive motility of both the BRL group and the ARL group increased slightly from 2009 until 2015 and then decreased back to baseline (p < 0.0001). This change offset the decrease in count seen in those years. A spurious change was observed with sperm morphology that declined after the first 2 years and remained stable thereafter (p < 0.0001, in both groups). However, this change was attributed to a contemporaneous change in the method of analyzing strict morphology which happened when the change occurred.

CONCLUSION

While statistically significant changes were found, clinically, these changes were quite mild and would not have been significant for fertility.