Decline in Semen Quality among Fertile Men in Paris during the Past 20 Years

BACKGROUND: Several studies have suggested a population-wide decline in the quality of semen over the past 50 years, but clear evidence for decreasing semen quality in recent decades is lacking. METHODS: From 1973 through 1992 we measured the volume of seminal fluid, the sperm concentration, and the percentages of motile and morphologically normal spermatozoa in 1351 healthy fertile men. The data on the semen samples were collected at one sperm bank in Paris. The data in each calendar year were analyzed as a function of the year of donation, the age of each patient, the year of birth, and the duration of sexual abstinence before semen collection. RESULTS: There was no change in semen volume during the study period. The mean concentration of sperm decreased by 2.1 percent per year, from 89 x 10(6) per milliliter in 1973 to 60 x 10(6) per milliliter in 1992 (P < 0.001). During the same period the percentages of motile and normal spermatozoa decreased by 0.6 percent and 0.5 percent per year, respectively (both P < 0.001). After adjustment in multiple regression analyses for age and the duration of sexual abstinence, each successive calendar year of birth accounted for 2.6 percent of the yearly decline in the sperm concentration and for 0.3 percent and 0.7 percent, respectively, of the yearly declines in the percentages of motile and normal spermatozoa (all P < 0.001). CONCLUSIONS: During the past 20 years, there has been a decline in the concentration and motility of sperm and in the percentage of morphologically normal spermatozoa in fertile men that is independent of the age of the men.