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Baisse de la production et de la qualite spermatique chez l’homme: Facteurs de variation et problemes méthodologiques
Factors modulating human sperm production and quality and methodological bias of studies on semen quality
Andrologie volume 8, pages 9–24 (1998)
Resume
Plusieurs travaux rétrospectifs publiés récement indiquent des évolutions séculaires différentes et des variations géographiques de la qualité du sperme humain. La responsabilité possible de facteurs professionnels ou environnementaux a souvent été évoquée. La controverse suscitée par ces travaux est importante. Il est souvent avancé que les études publiées sont sans valeur du fait des biais de recrutement ou des biais méthodologiques qu’elles contiennent. Tous ces travaux confirment la très grande variabilité intra- et interindividuelle des caractéristiques du sperme. Différents facteurs comme l’âge des hommes ou le délai d’abstinence sexuelle avant le prélèvement influencent la concentration de spermatozoïdes mais ils n’expliquent qu’une faible partie de la variabilité qui dépend aussi d’autres facteurs encore non identifiés. L’étude des facteurs de variation de la qualité du sperme est complexe car elle n’est pas exempte de biais. Le premier des biais possibles concerne la méthodologie même d’analyse du sperme, qui se caractérise par sa forte subjectivité, notamment en l’absence de procédures parfaitement standardisées. D’autres biais possibles sont dûs à l’hétérogénéité ou à la taille des populations étudiées, ou encore à la méthodologie statistique utilisée. A côté des études portant sur le sperme humain sujettes à de nombreuses critiques, différentes données d’observation chez l’homme et dans la faune sauvage et de récents travaux expérimentaux indiquent que l’hypothèse d’une dégradation de la fonction de reproduction mâle doit être prise au sérieux. Pour progresser dans l’étude des modifications éventuelles de la production et de la qualité spermatique, il apparaît donc urgent de développer des études prospectives minimisant tous les biais possibles. Parallèlement, des études expérimentales visant à étudier les facteurs suspectés de modifier la fonction de reproduction mâle doivent être entreprises dans le but d’une connaissance de la physiopathologie des mécanismes en causes.
Abstract
In the last few years, the possible decline of human semen quality as well as the important geographical variations of semen quality have been discussed in several scientific articles. In a meta-analysis of 61 publications worldwide, Carlsen et al. found a trend of decreasing sperm count over the past 50 years. This work has been at the origin of many commentaries and controversy. Two kinds of questions were mainly raised: Is the phenomenon real? what could be the reason(s) for such a decline? Many sceptical attitudes facing the conclusions of Carlsen et al. came from the fact that the studies included in the meta-analysis were done in various countries at different times, that the men studied could be very heterogeneous in term of fertility status and that the sample sizes of many studies were very low. It was also advocated that the results could be influenced by cofactors as the man’s age or the duration of sexual abstinence before semen collection or by differences in the methodologies used to analyse the semen samples in the various centers. Interestingly, several retrospective studies from a single centre were published after the meta-analysis of Carlsen reporting data from different groups of men recruited during more than 10 years periods in the last decades. Some of these studies found a decline of sperm concentration while for others, no secular modification of sperm concentration could be observed. It was also noticed important differences between values of semen characteristics in these various studies raising the question of geographical or regional differences besides the secular trend observed. Most of the published studies were very imprecis or poor of information concerning the men included in the study, the technical conditions used for semen analysis, the statistical methods used and the interpretation of the data. We discuss here some of the data of these studies in the context of the actual debate on the modifications of semen quality with the aim to pin-point the methodological bias contributing to the variation in the evaluation of semen quality. Moreover we also discuss the current data on the factors related to the men and their environment which could modulate sperm production and quality. It is mandatory to determine if the man’s reproductive function is influenced by environmental factors and if yes how they act. May be one of the main interest of the ongoing debate will be to develop basic and prospective epidemiological research in the field.
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Auger, J., Jouannet, P. Baisse de la production et de la qualite spermatique chez l’homme: Facteurs de variation et problemes méthodologiques. Androl. 8, 9–24 (1998). https://doi.org/10.1007/BF03034758
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DOI: https://doi.org/10.1007/BF03034758