Sperm crisis: what crisis?

or 20 years the so-called ‘‘sperm crisis’’ caused unrest among the public as well as the scientific community. Studies precipitated by this virtual crisis have refuted its existence, but have also illuminated hitherto neglected aspects of male reproductive function and indicated a need for prospective, long-term monitoring systems. Since 1992, the so-called ‘sperm crisis’ has lingered in the scientific literature and continues to agitate both media and the public. The basis for this sperm crisis is a publication from a Danish research group analysing 61 studies performed between 1938 and 1990 and concluding that sperm counts of otherwise healthy men had fallen drastically during the period of observation. It was even extrapolated that if the trend were to continue, sperm would totally disappear within the foreseeable future. This study, the ‘Carlsen study’ named after the first author, was and is heavily criticized regarding the study design, the heterogeneity of the investigated groups, the statistical evaluation, the nonstandardized methodology for semen analysis and varying times of abstinence. We do not want to repeat this criticism but just mention a few examples. While internal and external quality control has been introduced more or less ubiquitously in the clinical chemical laboratory, the andrology lab remained a neglected area in this effort towards quality assurance. This made results obtained from different laboratories and even from the same laboratory difficult to compare, which became strikingly evident when the World Health Organization (WHO) started to perform worldwide multicentre trials for male contraception and for male infertility treatment. Awareness of quality control in the andrology laboratory was stimulated by the publication of the WHO Laboratory Manual for Semen Analysis (first edition 1980 and fifth edition 2010). Under its influence and only over the last decade have programmes for external quality control been introduced. This has now progressed to the extent that for the first time in a multicentre study for male contraception, semen analysis has been partially centralized, thus avoiding interlaboratory variation. All these efforts have contributed to better comparability of semen parameters from different laboratories, but this type of standardisation certainly did not exist for the 61 papers reviewed in the Carlsen study. In addition, pre-analytical conditions also play an important role in the results of semen analysis. To a large extent, the number of spermatozoa in the ejaculate is correlated positively with the duration of abstinence, as shown in Figure 1. By varying abstinence times, sperm concentrations may be manipulated. If abstinence time is not properly recorded, the interpretation of semen parameters will be incorrect. Although abstinence time appears to be a simple parameter easily determined, the recorded figures are quite unreliable. When questioned concerning the time of abstinence since the last ejaculation, patients’ answers are often unreliable and the subject remains surrounded by taboos. In addition, actual sperm counts depend not only on the time of abstinence since the last ejaculation, but also on the frequency of ejaculations during the period preceding the actual investigation which makes the interpretation of results even more complicated. Changes in sexual behaviour and ejaculation frequency may have changed over the last 50 years and make historical comparisons notoriously difficult. Only recently and under the influence of the WHO manuals has more attention been paid to this variable, while abstinence time from older studies cannot be considered at face value. The study by Carlsen et al. showed the alleged decline of sperm counts in a figure which contained, however, only half of the data as circles (31 vs. 61). Moreover, the circles’ areas, reflecting the logarithm of the numbers of subjects per study, were wrong. The impression of the correct representation of the data is quite different from that of the original figure (Figure 2). The authors of the original study, despite agreeing that there was a ‘deficiency’ in the figure, classified this as being ‘qualitatively unimportant’ in their response. The comment and the reply were published in the same issue of British Medical Journal on 26 August 1995. It is disturbing to note that the same (and wrong) original figure was published again in the same year. Since that paper was accepted in September and published in December 1995, leaving ample time for corrections, one must conclude that the authors chose to ignore the suggested correction. Needless to say, the critical comment was not cited in that paper. Another methodological problem was raised by Handelsman. He reanalysed the data from the Carlsen study by using the median instead of the mean values of the respective studies to account for the skewed, not normally distributed data. The results of this reanalysis showed no significant decline in sperm counts. The shortcomings of the Carlsen study notwithstanding, it triggered 27 major studies taking ethnic and geographic differences into account. As a review by Fisch shows that 16 of these studies found no differences over time in sperm concentration, motility and morphology, five studies yielded ambiguous results and six studies demonstrated a decline in semen quality. Despite the criticism and although the majority of ensuing studies could not confirm the Carlsen hypothesis, the sperm crisis Centre of Reproductive Medicine and Andrology, University of Münster, Münster 48129, Germany and School of Engineering and Science, Jacobs University Bremen, Bremen 28759, Germany Correspondence: Professor E Nieschlag ([email protected]) Received: 18 July 2012; Revised: 26 July 2012; Accepted: 26 July 2012; Published online: 24 September 2012 F Asian Journal of Andrology (2013) 15, 184–186 2013 AJA, SIMM & SJTU. All rights reserved 1008-682X/13 $32.00