Sperm counts for men in the developed world have plummeted over the last 40 years, according to a compilation of studies by the journal Human Reproduction Update.
The report combined research on 42,935 men in 50 countries between 1973 and 2011.
In those nearly 40 years, men from North America, Europe, Australia, and New Zealand experienced a 59 percent drop in sperm count and a 52 percent decline in sperm concentration, while men in South America, Asia, and Africa saw little to no change in sperm count.
Sperm count refers to the total amount of sperm in an ejaculate, whereas sperm concentration is measured in each milliliter of fluid. The revelation that a high number of men have sperm concentrations below 40 million/mL means there is a significantly reduced likelihood of conception.
Researchers accounted for participant's fertility status, age, geographic location, and ejaculation abstinence time, among other influencing elements.
The study didn't focus on a cause, but experts speculate that exposure to chemicals in the modern world may be a factor in the dramatic drop.
CNN contributed to this report.