Critical appraisal of World Health Organization's new reference values for human semen characteristics and effect on diagnosis and treatment of subfertile men.

In 2010, the World Health Organization established new reference values for human semen characteristics that are markedly lower than those previously reported. Despite using controlled studies involving couples with a known time to pregnancy to establish the new limits, the reference studies are limited with regard to the population analyzed and the methods used for semen evaluation. The present review discusses concerns related to the new reference values for semen characteristics, including the effect on patient referral, diagnosis, and treatment of recognized conditions, such as varicocele, and on the indications for assisted reproductive technologies.