There are controversial claims that the sperm count of Western males is half of what it was in the 1950's, although one study claims American sperm counts are higher than they were in the 1970's. European men can now test their sperm count at home with a kit. Ironically, women are the most frequent buyers of the kit, perhaps because men are embarrassed to think that childlessness might be their fault.
The test produces a colour change that depends on the level of oxygen in the sperm sample. At low levels of oxygen the sperm count is high. At a sperm count of 20 million sperm per millilitre, a couple usually has a 90% chance of conceiving within one year. Infertile men usually have less than 10 million motile sperm per millilitre.
The quality of the sperm, and the fertility of his partner matter too. A man with a low sperm count can still produce many offspring if his partner is fertile. Male infertility is much harder to cure than infertility in women.