Human Reproduction, Vol 12, 2701-2705, Copyright © 1997 by Oxford University Press
DJ Handelsman
Controversial claims, based on a meta-analysis aggregating 61 heterogeneous
observational studies, have been made that human sperm output has decreased
by 50% over the last six decades and that this trend may be due to global
pollution. If true, such effects should be evident in all areas of the
globe; however, longitudinal studies within single centres in Europe and
America have produced conflicting results and there are no reports from the
southern hemisphere. We therefore reviewed semen analyses obtained from
1980-1995 from 689 healthy men volunteering for screening either as
potential sperm donors for a donor insemination programme (n = 509) or to
participate in five male contraception research studies (studies no. 1-5, n
= 180). All were recruited through the Andrology Unit of the Royal Prince
Alfred Hospital, Sydney, by the same doctors using standard methods of
recruiting, screening and laboratory examination throughout the period
1980-1995. Recruitment was by advertising without regard to marital or
fertility status except in two contraceptive efficacy studies (no. 1 and
no. 3) where participants had to be in a stable relationship requiring
contraception. Analysing the first semen sample individually or when
grouped by year of ejaculation, there was no significant difference in
sperm concentration over time or between years or according to year of
birth. During the second half of this period, 180 consecutive volunteers
were recruited by the same doctors and staff for five male contraception
studies. The median sperm concentration for studies no. 1 (103 x 10(6) ml)
and no. 2 (142 x 10(6) ml) were significantly (P < 0.05) higher than for
studies no. 3-5 (84, 67 and 63 x 10(6) ml, respectively) and for potential
sperm donors (median 69 x 10(6) ml). The inconsistency of these estimates
illustrates the magnitude of bias (up to 100%) in sperm output that may
occur in recruiting groups of self-referred volunteers within a single
centre. This highlights the invalidity of extrapolating similar findings on
sperm output of self-selected volunteers to the general male community or
in using such study groups to characterize sperm output in supposedly
'normal' men.
ARTICLES
Sperm output of healthy men in Australia: magnitude of bias due to self- selected volunteers
Royal Prince Alfred Hospital and Department of Medicine (D02), University of Sydney, NSW, Australia.
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