Abstract
Semen quality plays a pivotal role in sustaining the fertility rate and healthy population growth. Therefore, assessment of temporal trends in the semen quality provides valuable public health information. We analyzed the semen quality parameters of 5739 North Norwegian men among consecutive couples attending the fertility clinic of University Hospital of North Norway for investigation and/or treatment from 1993 to 2012. The seminal fluid volume, sperm concentration, and total sperm count were found to have gradually decreased during the past 20 years. The proportion of hypospermic, azoospermic, and oligozoospermic men had increased by 24.6% (p < 0.001), 109.5% (p < 0.001), and 9.5% (p = 0.05), respectively, in the last decade (2003–2012) compared to the first decade (1993–2002). The parameters of semen quality are rapidly deteriorating in North Norwegian men seeking fertility treatment.
Introduction
The semen quality is one of the fundamental determinants of reproductive success and well-being of future generation. Reports on the semen quality have been frequently published over the past several decades from different countries. A meta-analysis by Carlsen et al. (1992), which included 61 studies from all six continents during 50 years (1940–1990), initiated a debate among scientists and drew attention of the general population and politicians (Bromwich et al., 1994; Farrow, 1994). Reports on temporal trends in semen quality based on semen volume, sperm concentration, motility, and morphology have remained controversial since partly opposite conclusions were drawn using same data but alternative models for statistical analysis (Becker and Berhane, 1997; Olsen et al., 1995). Some studies have shown a decline in the semen volume and/or sperm cell concentration, motility, and morphology (Adamopoulos et al., 1996; Auger et al., 1995; Geoffroy-Siraudin et al., 2012; Irvine et al., 1996; Van Waeleghem et al., 1996; Younglai et al., 1998), while other similar studies have provided the opposite conclusion (Bujan et al., 1996; Fisch et al., 1996; Itoh et al., 2001; Paulsen et al., 1996; Rasmussen et al., 1997; Vierula et al., 1996). Several factors such as the genetic factors, environmental exposure, changes in lifestyle and food habit, oxidative stress, geographical distribution, and so on have been suggested to be associated with the changes in semen profile, however, no conclusive evidence has been found. Decline in semen quality may lead to a parallel increase in male infertility and subsequently demographic changes. Therefore, it is important to assess trends in semen quality. The objective of this study was to evaluate the temporal trends in semen quality using routinely collected clinical laboratory data of 5739 men who attended the fertility clinic of the University Hospital of North Norway over the past 20 years.
Materials and methods
Study population
The laboratory records and reports on semen analysis of all men who attended the fertility clinic of the University Hospital of North Norway from 1993 to 2012 were studied. The fertility clinic (IVF Unit) was established within the Department of Obstetrics and Gynecology in 1984. Semen analysis was performed as a routine procedure during the clinical investigation of subfertile/infertile couples. Complete records were available from 1993 onward. All subjects included in the study resided in the Northern region of Norway during the time of semen analysis. The study was considered as a quality assurance project not requiring Ethics Committee approval. The analysis of routinely collected clinical and laboratory data was approved by the data protection authority of the hospital (ref. 2015/2856).
Method of semen analysis
Men received both oral and written instructions and were requested to produce and submit a fresh semen sample after 3–5 days of sexual abstinence. Semen was analyzed using the conventional techniques adapted from the methods described in the third, fourth, and fifth editions of the World Health Organization (WHO) laboratory manuals (WHO, 1987, 1992, 2010) and the data were recorded according to hospital protocol. The protocol for measuring the volume, concentration, motility, and morphology of semen/sperm cells has not been changed significantly during the past 20 years. Semen volume was measured with a 5 mL plastic pipette, but in some cases, micropipette or 10 mL plastic pipette was also used. Sperm concentration and motility were assessed by direct observation of semen under a microscope after appropriate dilution (WHO, 1987, 1992, 2010). Morphology was assessed after Papanicolau staining and the aggregation was confirmed by mixed antibody reaction test for sperm cell antibodies.
Data analysis and statistics
The present study includes the results of all semen analyses performed at our laboratory over a period of 20 years. In some of the subjects, the semen analyses were carried out two or more times in the same year, and in such cases, the mean value per person was used for the purpose of statistical analysis. All analyses were performed by eight laboratory technicians using the same protocol. The percentage of motility was graded on a scale of 0–4; 3–4 for the spermatozoa that presented rapid progression along a linear track, 2 for slowly progressive or nonlinear, 1 for motile on the spot, and 0 for immotile. Morphology assessment was based on the criteria described in the WHO laboratory manuals (WHO, 1987, 1992, 2010). The measured seminal fluid volume of less than 1.5 mL was considered as hypospermia, the absence of spermatozoa observed in whole ejaculate as azoospermia, and the sperm cell concentration and total sperm cell count per ejaculate less than the reference values (15 × 106 sperm cells/mL and 39 × 106 sperm cells/ejaculate) as oligozoospermia. In addition to a yearly mean value of the seminal fluid volume, sperm cell concentration, and total sperm cell count per ejaculate, the mean values were also compared between the first decade (1993–2002) and the last decade (2003–2012). The proportion of hypospermia, azoospermia, and oligozoospermia were also compared between first and last decades. Data were analyzed using the SPSS 19.0 software (SPSS Inc. Chicago, Illinois, USA). Continuous variables are expressed as mean ± SD and categorical variables are reported as percentage. Temporal trends in semen characteristics were examined using a linear regression. The effect of men’s age and calendar year on semen characteristics was assessed using multiple regression models. Multiple coefficient of determination (R 2) is presented along with p value. Independent sample t test was used to assess differences between groups. A two tailed p value of <0.05 was considered significant.
Results
The numbers of subjects varied each year from a minimum of 180 to a maximum of 389 with a total of 5739 in 20 years. The youngest person was 20 years old and the oldest was 63 years. The mean age of the men seeking fertility treatment during the study period increased gradually from 32.0 ± 5.1 years in 1993 to 35.0 ± 7.9 years in 2012 (R 2 = 0.755, p < 0.001), respectively (Table 1). The recorded minimum seminal fluid volume was 0.1 mL and the maximum was 13.0 mL. The maximum mean seminal fluid volume was 4.0 ± 1.9 mL (n = 281) in 1993 and the minimum mean seminal fluid volume was 2.7 ± 1.4 mL (n = 303) in 2011 (R 2 = 0.707, p = 0.002). A gradually decreasing trend of mean seminal fluid volume was observed during the study period (Table 1). The highest sperm count was 670.0 × 106 sperms/mL. The maximum mean sperm cell count was 56.2 × 106 sperms/mL (n = 360) in 1997 and a gradually decreasing trend was observed with the minimum mean sperm cell count of 35.9 × 106 sperms/mL (n = 323) in 2009. A gradually decreasing trend of total sperm count per ejaculate was observed during the study period (R 2 = 0.660, p < 0.001). The mean total sperm count per ejaculate decreased from 189.9 × 106 in 1993 (the highest) to 98.6 × 106 (the lowest) in 2009 (R 2 = 0.892, p < 0.001; Table 1).
Semen profile (volume, sperm cell concentration per milliliter, and total sperm cell count per ejaculation) of North Norwegian men from 1993 to 2012.a
aData are expressed as mean ± SD (n = number of subjects).
The mean seminal fluid volumes in the first decade (1993–2002) and the last decade (2003–2012) were 3.5 ± 1.7 (n = 2749) and 3.1 ± 1.5 mL (n = 2990), that is, a 11.4% decrease (p = 0.014). The mean sperm cell concentrations in the first decade (1993–2002) and the last decade (2003–2012) were 52.0 × 106 and 40 × 106 sperms/mL, respectively, that is, a 23.1% decrease (p < 0.001). The total sperm count in the first decade was 166.0 × 106 sperms per ejaculate, which decreased by 28.9% (p < 0.001) in the last decade (Figure 1).
Comparison of the semen profiles between the first decade (1993–2002) and the last decade (2003–2012) of the study. The results are expressed as the mean values of n = 2749 for the first decade (1993–2002) and n = 2990 for the last decade (2003–2012).
The distribution pattern of hyposermic, azoospermic, and oligozoospermic population from 1993 to 2012 is shown in Table 2. The proportion of hyposermic, azoospermic, and oligozoospermic population has been found to be in gradually increasing order from 1993 to 2012 among the north Norwegian men who approached the University hospital for the infertility treatment. The percentage of hypospermic and azoospermic population was found to be sharply increased than oligozoospermic population.
Distribution pattern of hyposermia, azoospermia, and oligozoospermia among the North Norwegian men from 1993 to 2012 who approached for the infertility treatment.
The proportion of hypospermic men in the beginning of the study period was 6.8% (n = 281) and it increased with a rate of 4.4% per year to 16.5% (n = 333) in 2012 (Figure 2). The proportion of hypospermic population in the first decade (1993–2002) was 12.2%, which increased by 24.6% (p < 0.001) reaching 15.2% in the last decade (2003–2012). Similar increasing trends were also observed for the azoospermic and oligozoospermic men. The proportion of azoospermic men increased from 6.3% in the first decade to 13.2% in the last decade (p < 0.001). Similarly, the proportion of oligozoospermic men was 26.4% in the first decade, which increased by 9.5% (p = 0.05) to 28.9% in the last decade (Figure 3).
Percentage of hypospermic population in North Norwegian men from 1993 to 2012. The bar represents the percentage of hypospermic males who attended to the hospital for infertility treatment on the particular year, as described in Table 1.
Comparison of hypospermic, azoospermic and oligozoospermic North Norwegian men seeking infertility treatment from 1993 to 2012. The results are expressed as the percentage values and compared between the first decade (1993–2002, n = 2749) and the last decade (2003–2012, n = 2990).
Discussion
Infertility pertains approximately 15% of sexually active couples and the quality of semen/sperms contributes significantly to the fertility potential. The total number of spermatozoa per ejaculate and the sperm cell concentration are related to time required to achieve pregnancy (Slama et al., 2002) as well as pregnancy rates (Zinaman et al., 2000) and are predictors of conception (Bonde et al., 1998; Larsen et al., 2000). Several factors such as man’s age, health status, duration of his sexual abstinence before the collection of semen, and so on, can influence the characteristics of the semen (Jouannet et al., 1981; Schwartz et al., 1983). A wide variation in semen profile, expressed as the total number of spermatozoa and sperm cell concentration, was observed in a longitudinal study of five individuals who had semen analysis twice a month for one-and-a-half-year period (WHO, 2010). In spite of individual variations, the present study clearly shows a gradual change of semen profile in our study population over two decades.
The mean seminal fluid volume (2.9 ± 0.1 mL) in the periods of last 4 years (2009–2012) was 26.0% less compared to that of the period of first 4 years (1993–1996). The mean seminal fluid volume in the first decade (1993–2002) had decreased by 11.4% compared to that of the last decade (2003–2012). Our data demonstrate a gradual decrease in the seminal fluid volume among men seeking fertility treatment in Northern Norway over the past 20 years (Table 1 and Figure 1).
Carlsen et al. reported a significant decrease in the sperm cell count from 113 × 106 mL−1 in 1940 to 66 × 106 mL−1 in 1990 and the mean seminal fluid volume from 3.4 mL to 2.75 mL, respectively (Carlsen et al., 1992). However, the data included in the analysis were heterogeneous and included both healthy as well as infertile men. Auger et al. reported the mean sperm cell concentration of 89 × 106 mL−1 in 1973 and 60 × 106 mL−1 in 1992, indicating a decrease by 2.1% per year among healthy sperm donors in Paris (8) who had fathered at least one child previously. In our study among men seeking fertility treatment, the mean sperm cell concentration and total sperm cell count in the last decade (2003–2012) had decreased by 23.1% and 28.9%, respectively, compared to that of the first decade (1993–2002). However, it is interesting to note that the semen volume and sperm cell concentration reported in the last period of the study (1992) by Auger et al. (1995) were similar to the corresponding data in the earlier period (1992) of our study. Furthermore, the proportion of hypospermic men in our study population had doubled in the last 20 years with the rate of 4.4% per year (Figure 2). Similar trends were also observed for the azoospermic and oligozoospermic population (Figure 3). The results of our study showed a similar temporal trend of deteriorating semen quality as reported by others two decades ago (Auger et al., 1995; Carlsen et al., 1992) irrespective of the population studied.
As our study was performed in a self-selected population of men seeking fertility treatment, the results may not be applicable to the general population. Additionally, as the mean age of men seeking fertility treatment increased from 32.0 years to 35.6 years, it could be argued that the decreasing semen quality is due to increasing age. However, regression analysis showed that that the patient’s age had no significant effect on the semen quality. According to Kidd et al., decreases in the semen volume (3–22%), sperm cell motility (3–37%), and percent normal spermatozoa (4–18%) are likely when comparing the 30-year-old to 50-year-old men; however, the semen quality among the male population aged 32 and 36 years is not significantly different (Kidd et al., 2001). Therefore, the change in the mean age is unlikely to have contributed significantly to the semen profile changes seen in our study.
Several studies have shown that the sperm cell motility, more particularly the percentage of spermatozoa with ‘grade 3–4’ motility, is the strongest indicator of the potential in vivo fertilizing capacity of semen (Comhaire et al., 1994). In the fertility clinics, including ours, even the low-grade motility sperm cell can be used to successfully fertilize an ovum using intracytoplasmic sperm injection. However, the relationship between pregnancy outcome and sperm motility remains inconclusive. As sperm motility and morphology are evaluated subjectively, these data are not presented in the present article.
Our study did not allow us to identify the possible cause(s) of the observed deterioration in the semen quality. Cigarette smoking has been found to be associated with a significant decrease in sperm cell concentration (−15.3%), total sperm cell count (−17.5%), total number of motile sperm cells (−16.6%), and citrate concentration (−22.4%) (Kunzle et al., 2003). We did not have information on the lifestyle factors on these men, but the changes in the lifestyle can hardly be held responsible for deteriorating trend of semen quality, particularly since the consumption of, for example, tobacco seems to have decreased in the overall population (Bartecchi et al., 1994).
It can be speculated that environmental factors might be responsible for the observed deterioration of semen characteristics (Jensen et al., 1995; Sharpe and Skakkebaek, 1993; Vanhoorne et al., 1994). Geoffroy-Sirauddin et al. speculated the decline of semen quality due to the heavy industrial pollution in Marseille, France (Geoffroy-Siraudin et al., 2012). In general, North Norway is considered to be a less polluted region with no noticeable heavy industries. However, the trend of changing semen profile observed in North Norway appears to be similar to that in the big cities (Adamopoulos et al., 1996; Auger et al., 1995; Geoffroy-Siraudin et al., 2012; Irvine et al., 1996; Van Waeleghem et al., 1996; Younglai et al., 1998). Therefore, it might be due to several other factors rather than environmental pollution. It has been suggested that the acute exposure to radiofrequency fields of cellular phones may modulate the oxidative stress of free radicals by enhancing lipid peroxidation and cause a decrease in the activity of the antioxidants, superoxide dismutase, and glutathione peroxidase, in human erythrocytes (Moustafa et al., 2001). In addition, genotoxic effect on epididymal spermatozoa has been reported when mice were irradiated 12 h per day by radiofrequency for 7 days (Aitken et al., 2005). Use of laptop computer connected to Internet through Wi-Fi is also reported to decrease human sperm cell motility and increase in DNA fragmentation by enhancing oxidative stress (Avendano et al., 2012). However, it should be noted that there are several reports showing declining semen quality in 1940–1990 period (Auger et al., 1995; Carlsen et al., 1992), and at that time, there were no laptop computers or Wi-Fi. Therefore, there is no direct evidence to claim that the use of computers and mobile phones is responsible for the change in semen profile; however, a closer evaluation may be worthwhile.
Population migration has significantly increased over the last 20 years in North Norwegian region. Our analysis does not distinguish indigenous population from immigrated one. Therefore, the possibility of changes in semen profile due to the demographic changes cannot be excluded. Moreover, present results on semen analysis were taken from the men among couples seeking infertility treatment and not from the healthy population. Therefore, arguably the same trend of semen quality decline might not be observed in the healthy population.
Conclusion
In this study, we found that the semen quality of men among couples seeking fertility treatment is progressively declining. However, the causes of semen quality deterioration and its effect on fertility potential remain to be elucidated. Further studies are needed to clarify temporal trends in semen quality in the general population of the Arctic region.
Footnotes
Acknowledgements
The authors would like to acknowledge Dr Ranjan Parajuli, Department of Community Medicine, UiT-The Arctic University of Norway, Tromsø, for his help with statistical analysis.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.