For 50 years, the World Health Organization has adopted the standard of "20 million sperm per kilogram (1 ‰ liter) of semen, of which at least half are motility", which is widely used to determine male fertility.
Researchers at the University of Rochester School of Medicine collected semen from 765 pregnant couples and 696 spouses of those who had already given birth across the United States as research subjects. It was found that some men with sperm numbers below the World Health Organization standards can still conceive their wives, while others above the standard are unable to conceive due to the incorrect shape of the sperm.
The original "normal" sperm head should be elliptical, with a very straight and swinging tail. If the head is round, biased, too large or too short, and the tail is bent or twisted, it is an "abnormal" shape. Researchers have found that each handful of semen contains more than 48 million sperm, of which 63% are capable of swimming, and 12% of men with normal shapes have no problem with fertility. If there are less than 13.5 million sperm per male pinch, with no more than 32% capable of motility, and less than 9% with a "beautiful" shape, the chances of infertility are high.