Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries

Abstract

BACKGROUND Numerous studies have reported declines in semen quality and other markers of male reproductive health. Our previous meta-analysis reported a significant decrease in sperm concentration (SC) and total sperm count (TSC) among men from North America–Europe–Australia (NEA) based on studies published during 1981–2013. At that time, there were too few studies with data from South/Central America–Asia–Africa (SAA) to reliably estimate trends among men from these continents. OBJECTIVE AND RATIONALE The aim of this study was to examine trends in sperm count among men from all continents. The broader implications of a global decline in sperm count, the knowledge gaps left unfilled by our prior analysis and the controversies surrounding this issue warranted an up-to-date meta-analysis. SEARCH METHODS We searched PubMed/MEDLINE and EMBASE to identify studies of human SC and TSC published during 2014–2019. After review of 2936 abstracts and 868 full articles, 44 estimates of SC and TSC from 38 studies met the protocol criteria. Data were extracted on semen parameters (SC, TSC, semen volume), collection year and covariates. Combining these new data with data from our previous meta-analysis, the current meta-analysis includes results from 223 studies, yielding 288 estimates based on semen samples collected 1973–2018. Slopes of SC and TSC were estimated as functions of sample collection year using simple linear regression as well as weighted meta-regression. The latter models were adjusted for predetermined covariates and examined for modification by fertility status (unselected by fertility versus fertile), and by two groups of continents: NEA and SAA. These analyses were repeated for data collected post-2000. Multiple sensitivity analyses were conducted to examine assumptions, including linearity. OUTCOMES Overall, SC declined appreciably between 1973 and 2018 (slope in the simple linear model: –0.87 million/ml/year, 95% CI: –0.89 to –0.86; P < 0.001). In an adjusted meta-regression model, which included two interaction terms [time × fertility group (P = 0.012) and time × continents (P = 0.058)], declines were seen among unselected men from NEA (–1.27; –1.78 to –0.77; P < 0.001) and unselected men from SAA (–0.65; –1.29 to –0.01; P = 0.045) and fertile men from NEA (–0.50; –1.00 to –0.01; P = 0.046). Among unselected men from all continents, the mean SC declined by 51.6% between 1973 and 2018 (–1.17: –1.66 to –0.68; P < 0.001). The slope for SC among unselected men was steeper in a model restricted to post-2000 data (–1.73: –3.23 to –0.24; P = 0.024) and the percent decline per year doubled, increasing from 1.16% post-1972 to 2.64% post-2000. Results were similar for TSC, with a 62.3% overall decline among unselected men (–4.70 million/year; –6.56 to –2.83; P < 0.001) in the adjusted meta-regression model. All results changed only minimally in multiple sensitivity analyses. WIDER IMPLICATIONS This analysis is the first to report a decline in sperm count among unselected men from South/Central America–Asia–Africa, in contrast to our previous meta-analysis that was underpowered to examine those continents. Furthermore, data suggest that this world-wide decline is continuing in the 21st century at an accelerated pace. Research on the causes of this continuing decline and actions to prevent further disruption of male reproductive health are urgently needed.

What Does Intracytoplasmic Sperm Injection Change in Embryonic Development? The Spermatozoon Contribution

“…The future development of non-invasive diagnostic instruments of the spermatozoon in order to know its biochemical structure and DNA/RNA content before microinjection would be determinant on the understanding of spermatogenesis, as well as the consequences of male infertility causes and an unfavorable environment on the building of a competent spermatozoon. In a world in which sperm quality has not stopped declining through the decades and in different continents due to adverse environments [ 108 ], a responsible and global commitment to resolving male infertility issues is the only way to improve male fertility and resolve couple fertility without ART.…”

Impact of Fetal Exposure to Endocrine Disrupting Chemical Mixtures on FOXA3 Gene and Protein Expression in Adult Rat Testes

“…The etiology of male infertility includes defects in sperm quality, low sperm count, ductal obstruction or dysfunction, or hypothalamic–pituitary axis disturbances [ 3 , 4 ]. Researchers have found lower sperm counts and decreased quality of semen in certain geographical regions, suggesting the influence of socioeconomic, nutritional, and/or environmental differences [ 1 , 5 ]. Decreased quality of semen has also been found to coincide with increasing incidence rates in male genital tract abnormalities such as cryptorchidism, a major risk factor for testicular cancer [ 6 , 7 ].…”

Epigenetics Role in Spermatozoa Function: Implications in Health and Evolution—An Overview

“…Specifically, reproductive problems are a concerning and growing health problem affecting around 15% of couples worldwide, where male partners are responsible for 20–30% of the overall infertility cases [ 34 ]. The decline of male fertility is a worldwide matter of concern since available studies suggest a lower semen quality over the years [ 35 ], thus being related to infertility problems. To deal with these situations, assisted reproduction techniques (ART) have been developed to help to solve part of these problems.…”