Temporal trends in sperm count: a systematic review and meta-regression analysis
by Hagai Levine et al
Human Reproduction Update 2017;
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.
To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration and total sperm count, and their modification by fertility and geographic group.
A total of 244 estimates of sperm concentration and total sperm count 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 [including global region, age, ejaculation abstinence time, semen collection method, method of measuring and more].
This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by sperm concentration and total sperm count) 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.