Table 3. Studies presenting ambiguous results (total sample size=26 007).
Year | First author | Sample size (N) | Study period | Location | Major findings |
---|---|---|---|---|---|
1995 | Comhaire46 | 360 | NA | Belgium | 1. Motility and morphology exhibited ‘highly significant decreases'. |
2. Total sperm count did not decrease. | |||||
3. 40% of donors after 1990 exhibited ‘subnormal' sperm compared with only 5% of group investigated before 1980. | |||||
1996 | van Waeleghem47 | 416 | NA | Belgium | 1. Volume increased slightly. |
2. Mean concentration declined by 12.4 million per ml in study period. | |||||
3. Sperm count was unchanged. | |||||
4. Normal morphology decreased from 39.2% in 1977–1980 to 26.6% in 1990–1995. | |||||
1996 | de Mouzon48 | 7714 | 1989–1995 | France | 1. No decline in sperm counts when data were analyzed by year of collection. |
2. Sperm counts declined ‘regularly' for men born from 1950 to 1975. | |||||
1997 | Zheng49 | 8608 | 1968–1992 | Denmark | 1. Semen quantity and quality did not decline with increasing year of birth during the entire period from 1922 to 1972. |
2. From 1950 onward there was a gradual decline in sperm count and normal sperm forms but not in semen volume. | |||||
3. Decline in total sperm count was 1.9 million per ml per year of advancing year of birth. | |||||
1999 | Ulstein50 | 5180 | 1975–1994 | Norway | 1. Two subgroups of study subjects showed declines in semen parameters. |
2. Subgroup of men with previous children did not show decline in semen parameters. | |||||
2010 | Mukhopadhyay51 | 3729 | 1981–1985–2000–2006 | India | 1. Mean semen concentration rose from 84×106 per ml in 1980s to 87×106 per ml in 2000s. |
2. Volume declined slightly from mean of 2.97 ml to 2.7 ml. | |||||
3. Motility declined slightly from 60.6% to 58%. |
Abbreviation: NA, not applicable.