Statistical analysis in andrology

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

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.

Temporal trends in sperm count: a systematic review and meta-regression analysis

BACKGROUND

Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality.

OBJECTIVE AND RATIONALE

To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group.

SEARCH METHODS

PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981-2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973-2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group ('Unselected by fertility' versus 'Fertile'), geographic group ('Western', including North America, Europe Australia and New Zealand versus 'Other', including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models.

OUTCOMES

SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models -0.70 million/ml/year; 95% CI: -0.72 to -0.69; P < 0.001; slope in adjusted meta-regression models = -0.64; -1.06 to -0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (-1.38; -2.02 to -0.74; P < 0.001) and among Fertile Western (-0.68; -1.31 to -0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (-5.33 million/year, -7.56 to -3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (-2.06 million/ml, -3.38 to -0.74; P = 0.004 and -8.12 million, -13.73 to -2.51, P = 0.006, respectively).

WIDER IMPLICATIONS

This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50-60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

The mast cells in semen: their effects on sperm motility

This study was conducted to evaluate any possible association between mast cells and sperm concentration, morphology, and motility. The study comprised 400 patients who had applied for semen analysis. To evaluate mast cells, 6 smear slides were prepared for each subject and stained with 1% toluidin blue-pyronine (pH 4). The slides revealing any mast cells were labeled as mast+. Concentration and motility was evaluated through a Makler chamber. Kruger's strict criteria were used in morphometric analysis. The mean age of 86 mast+ cases (21% of total patients) was 31+/-6.7; progressive sperm motility rate was 33+/-21.2. The mean concentration was 32+/-30.2 x 10(6)/mL, and normal sperm percentage was 11.8+/-6.5. Progressive sperm motility rate in the mast- cases were 53+/-25. The mean age of mast cell+ patients was higher than that of mast cell- patients (t=3.57, p<.001), while they had lower sperm concentration (p>.05) and lower normal morphologic sperm rate (t=2.26, p<.024), compared to mast cell- patients. The relation between mast cell+ and mast cell- cases and sperm progressive motility was statistically significant (t=6.44, p<.001). It was concluded that sperm parameters were negatively affected by mast cells.

Percutaneous varicocele embolization in the treatment of infertility

Clinical and sub-clinical varicoceles are associated with infertility and abnormal sperm parameters. Percutaneous embolization is a minimally invasive, safe, outpatient method of treatment which is cost effective in comparison to surgery. This study is a retrospective review of embolization of the spermatic vein using stainless steel occluding spring coils, performed in 116 males from two infertility clinics. Follow-up results were complete in 87 patients of which 79 (91%) were successful both technically and clinically and all had sperm analysis performed both before and within 2 years after embolization. There was a highly significant increase in motility (mean 35% before, mean 46% after, p < 0.001). Sperm density showed a trend towards improvement, but only p < 0.10, and there was no significant change in semen volume or morphology. The partners of 29 men (33%) became pregnant in a total of 241 years of follow-up.

Computer assisted sperm motility analysis at the moment of induced pregnancy during gonadotropin treatment for hypogonadotropic hypogonadism

Two azoospermic patients with isolated hypogonadotropic hypogonadism (IHH) no. 1,24-year-old, and no. 2,31-year-old), never treated before, were given gonadotropin therapy (GT), (FSH, 225 IU/week, and HCG, 4000 IU/week) and followed up monthly for sperm characteristics. After 6 (no. 1) and 9 (no. 2) months of treatment, immotile spermatozoa appeared in the semen. Two months later motile spermatozoa also appeared. A motile sperm concentration sufficiently high for computer motion analysis (CASA) was achieved 1 month later 9th and 12th month, respectively. At the 13th (no. 1) and 17th (no. 2) month of GT, CASA showed a small population of spermatozoa with a very good motility pattern. In the next ovulatory cycle the patients' partners became pregnant.

Statistical andrology: standard semen analysis and computer-assisted sperm motility analysis

Results are reported of a statistical evaluation of the variables obtained by standard microscopic semen analysis and by computer-assisted sperm motility analysis. Descriptive statistical analysis and cluster analysis were carried out on both sets of data. A contingency table was created to compare the classifications obtained by the two clustering procedures. A canonical correlation analysis was performed to evaluate the classification power of the variables obtained by the two semen analyses. The results show that the two techniques of semen analysis are complementary and not substitutive and that the correlated variables "percentage forward motility" and "sperm velocity" are the most discriminating.