През последните десетилетия няма доказателства за стабилна тенденция към намаляване на показателите, отчитащи качествата на семенната течност:
Rasmussen PE, et al. “No evidence for decreasing semen quality in four birth cohorts of 1,055 Danish men born between 1950 and 1970”. Fertil Steril (US), Dec 1997, 68(6) p1059-64
Berling S, Wolner-Hanssen P. “No evidence of deteriorating semen quality among men in infertile relationships during the last decade: a study of males from Southern Sweden. Hum Reprod (England), May 1997, 12(5) p1002-5