Is seminal quality worsening? A 20-year experience in Córdoba, Argentina

Abstract

Purpose

To assess the possible variations in semen quality during the last 20 years in Córdoba, Argentina, and to identify possible causal lifestyle or genitourinary factors.

Methods

Retrospective study of 23,130 patients attending an andrology laboratory. The 20-year period (2001–2020) was divided into four quinquenniums. Seminal parameters (sperm concentration, motility, morphology, viability, and membrane functional integrity) were classified as normal or abnormal according to WHO, and results were expressed as percentage of patients abnormal for each parameter per quinquennium. In addition, the percentage of patients per quinquennium exposed to the different risk factors (daily alcohol and/or tobacco consumption; occupational exposure to heat or toxics; history of parotitis or varicocele; and high body mass index, BMI) was reported.

Results

Patients included in our study did not show impairment in seminal quality over time. Beyond a transient decrease in normozoospermia in the second and third quinquennium, possibly explained by a parallel increase in teratozoospermia, other important parameters of the spermogram did not change. In fact, abnormalities in sperm concentration (oligozoospermia), total sperm count, viability and response to hypoosmotic test showed a decreasing trend over time. On the other hand, parotitis, varicocele, morbid obesity and regular exposition to heat/toxics were the factors more frequently associated with semen abnormalities; the last two increased their frequency over the study period.

Conclusion

The population included in this study did not show a clear impairment in semen quality during the last 20 years. The decreasing patterns found were associated with high BMI and exposure to heat/toxics.

Introduction

While the first paper reporting a decline in semen quality was published early in 1974 by Nelson and Bunge [1], it was not until 1992 when the meta-analysis by Carlsen et al. [2] raised the alarms and initiated the debate. In this meta-analysis including almost 15,000 men with no history of infertility, the authors reported that between 1938 and 1991, the average sperm count decreased significantly from 113 to 66 million/ml. The conclusions reached by Carlsen et al. [1992] were criticized by several authors [3–5] and some of them even argued that, given the number of methodological flaws encountered, the study should not be included in any data review supporting a decline in semen quality [6].

Despite all critics, the report from Carlsen et al. [2] was fundamental since it prompted researchers to explore the issue of semen quality in their own regions. Subsequent studies showed conflictive findings, yielding both supporting [7–11] and opposing evidence [12–14]. In fact, several authors have reported an improvement in some seminal parameters over the years [15–19].

Some hypotheses have been proposed to explain the controversial results obtained so far, geographic and temporal variability, the existence of possible confounding factors, and/or the heterogeneity of the cohorts enrolled [20]. Moreover, studies may be influenced by the use of the different World Health Organization (WHO) guidelines published over the years (1980, 1987, 1992, 1999, 2010, and 2021). In addition, some studies have compared data collected from just two different years [17, 18, 21] rather than analyzing trends over time.

Although inconclusive, those reports in favor of a decline in semen quality raise the question of the threatened status of male fertility. And given that semen quality has been suggested to be a biological marker of long-term morbidity and mortality [22, 23], from the perspective of regional disease prevention and control, it would be helpful to establish the trends in semen quality for each population.

In Latin America, available information on variations of semen quality is scarce. In a recent review, Sengupta et al. [24] pooled 138 studies from different countries published between 1930 and 2015 and stated that “only a handful of studies have been conducted involving regions of South America” in order to assess seminal quality trends. From the seven studies from South America included in this review, only one was conducted in Argentina, by our group, and six were performed in Brazil. Other papers reporting seminal quality trends in South America were developed in Venezuela [25] and Uruguay [19].

Conversely, when exploring the etiology of semen quality decline, despite a description of the numerous risk factors that may influence sperm function [26, 27], relative trends over time have been barely studied.

Therefore, the main objective of this study was to retrospectively analyze the possible variation in semen quality during the last 20 years in more than 23,000 patients attending an andrology center in Córdoba, Argentina, and to identify possible causal lifestyle and/or genitourinary factors.

Materials and methods

Patients

This retrospective, longitudinal, and correlational study evaluated semen quality in male members of couples undergoing fertility evaluation at the Andrology and Reproduction Laboratory in Córdoba, Argentina, from January 2001 to December 2020. This laboratory is accredited and regularly controlled for quality by the “Programa Externo de Control de Calidad, Fundación Bioquímica Argentina” and the “Sociedad Argentina de Medicina Reproductiva (SAMER).”

All the patients included in this study signed a written informed consent allowing the use of their data for statistical and scientific purposes. Since this study included non-invasive procedures and semen samples were voluntarily provided by the patients and kept rigorously anonymous, approval by an institutional review board was not mandatory. Principles outlined in the Declaration of Helsinki regarding human experimentation were met. Furthermore, the andrology laboratory, the research institute, and their head researchers are certified by the local authority committee (Consejo de Evaluación Ética de Investigación en Salud, COEIS; and Registro Provincial de Investigación en Salud, RePis), with center numbers 122 and 109, respectively, and researcher numbers 501 and 1055, respectively.

All patients fulfilled a form with information on age, abstinence period, alcohol and tobacco consumption, occupational exposure to heat or hazardous substances (pesticides or radiations), and history of genitourinary diseases that can affect the hypothalamic-pituitary-testicular axis. Exclusion criteria were incomplete data, azoospermia, abstinence out of range (2–7 days), and age out of range (younger than 20 or older than 60 years, respectively). After applying these exclusion criteria, the final number of semen samples (one sample per patient) was 23,130.

Data on daily alcohol and tobacco consumption, exposure to heat/toxics, and history of parotitis or varicocele were obtained from the previously mentioned form. For alcohol consumption and according to previous studies [28, 29], patients were grouped as follows: non-drinkers,1–2 glasses per day, and ≥3 glasses per day. It is important to remark that each patient informed the number of glasses consumed per day without detailing the type of beverage. For tobacco consumption, patients were grouped as follows: non-smokers, 1–10 cigarettes/day, and >10 cigarettes/day. Varicocele status was categorized as 0 (no varicocele), varicocele grades 1, 2, or 3 (G1, G2, and G3), and surgically resolved (SR) [29–31].

Weight and height of the patients were measured and recorded on the same day that the semen sample was obtained and processed. Body mass index (BMI) was calculated as mass (kg) divided by height squared (m²). Patients were then classified into five groups: underweight (UW; BMI <18.5 kg/m²), normal weight (NW; BMI 18.5–24.9 kg/m²), overweight (OW; BMI 25–29.9 kg/m²), obese (OB; BMI 30–39.9 kg/m²), and morbidly obese (MOB; BMI ≥40 kg/m²) [32]. These data were available only since 2006.

Semen parameters evaluated

After 2–7 days of abstinence, semen samples were collected by masturbation into sterile containers. When necessary, samples were transported to the laboratory at approximately 37°C; in all cases, the samples were analyzed within the first hour after collection by the same two experienced operators.

After liquefaction, semen analysis was performed according to the WHO recommendations [33] except for volume and motility evaluation. Briefly, seminal volume was determined in a graduated conic tube. Sperm concentration and motility were evaluated in a Makler counting chamber [34] and classified as rapid or total progressive motility (rapid plus slow progressive). For each patient, these quantifications were made by triplicate (loading the chamber three times), reporting the mean value. Total sperm count was calculated as semen volume × sperm concentration. Furthermore, total motile sperm count (TMSC) was calculated as percentage of progressive motile sperm × total sperm count/100. Sperm viability was determined with the supravital eosin Y technique [35] and membrane functional integrity was evaluated using the hypoosmotic swelling test (HOST) [36]. Sperm chromatin condensation (nuclear maturity) was tested with aniline blue technique [37] and sperm morphology was assessed by strict criteria with Papanicolau staining [38].

Statistical analysis

Statistical analyses were performed using InfoStat 2017 (Universidad Nacional de Córdoba, Córdoba, Argentina) and SPSS 20.0 (IBM Corp., Armonk, NY, USA). In all cases, p<0.05 was considered significant.

The 20-year period was divided into four quinquenniums (Q1: 2001–2005; Q2: 2006–2010; Q3: 2011–2015 and Q4:2016–2020). For all patients, each seminal parameter was classified as normal or abnormal according to the WHO criteria [33] and the results were expressed as the percentage of patients that yielded abnormal results for each seminal parameter. Of note, the lower reference for TMSC was calculated as total sperm count lower reference × progressive motility lower reference; for rapid progressive motility, we considered the 5%, as previously reported [39]. Additionally, data of abnormalities in sperm concentration, total progressive motility, and morphology were used to calculate the percentage of patients with normozoospermia or those with oligo-astheno-teratozoospermia (OAT).

On the other hand, the percentage of patients per quinquennium that were exposed to the different risk factors was informed in order to visualize, for example, if the presence/severity of varicocele increased/decreased along time, or if the frequency of obesity increased/decreased. Differences in proportions were analyzed using the chi-squared independence test and logistic regression (adjusted by age and days of abstinence). In order to identify values that were significantly higher (marked with a +) or lower (marked with a −) than expected under independence, standardized residuals greater than 1.96 or lower than −1.96 were used according to Agresti [40].

Finally, in order to assess the possible association between seminal parameters and risk factors, a chi-square test was performed.

Results

Table 1 summarizes the general characteristics of the 23,130 patients included in this study in terms of mean values and frequency of semen abnormalities.

Table 1.

General characteristics of patients included in this study

Characteristics	Mean± SEM	Percentage of abnormal patients
Age (years)	35.42±0.04	–
Abstinence period (days)	3.94±0.01	–
Semen volume (ml)	3.02±0.01	11.98
Ph	7.66±0.001	1.37
Sperm concentration (× 106/ml)	68.10±0.40	13.82
Total sperm count (× 106)	186.60±1.14	15.02
Progressive motility (%)	47.84±0.12	20.10
Total motile sperm count (× 106)	101.75±73.26	1.88
Viability (%)	16.97±0.07	0.98
Normal morphology (%)	6.14±0.03	33.01
Reactive to HOST (%)	79.54±0.07	2.48

Males included in this study (n=23,130) were members of couples undergoing fertility evaluation at the Andrology and Reproduction Laboratory in Cordoba, Argentina, from January 2001 to December 2020. Values are expressed as mean±SEM and as percentage of patients with abnormal results for each seminal parameter. HOST hypoosmotic swelling test

Table 2 shows the percentages of patients per quinquennium that exhibited values under the normal range for each parameter. Results in bold are those that were statistically significant, identifying also those that were higher (+) or lower (−) than expected under independence. The sign of the slope indicates the pattern of the trend; positive means increasing probability of abnormalities over time and negative means decreasing probability of abnormalities over time (except for normozoospermia that should be interpreted the other way around), and the value of the slope indicates the degree of change (increase or decrease) between quinquenniums. As it can be seen in Table 2, there was a decrease in the frequency of normozoospermia in Q2 compared to Q1 and Q4; teratozoospermia showed a similar profile. We detected also an increasing pattern over time on hypospermia. Other sperm variables showed a decreasing pattern in the frequency of abnormalities, including sperm concentration (oligozoospermia), total sperm count, viability, and HOST. Asthenozoospermia did not show significant variations in its prevalence over time. However, when assessing abnormalities in rapid progressive motility, we found a significant increasing pattern in prevalence over time (Q1: 23.17 (−); Q2: 29.53 (−); Q3: 34.40 (non-significant); and Q4: 42.14 (+); p<0.0001; slope: 0.27).

Table 2.

Frequency of patients with abnormal results for each seminal parameter, divided into quinquenniums

Semen abnormality	Quinquennium 1	Quinquennium 2	Quinquennium 3	Quinquennium 4	Chi-square p value	Logistic regression slope
Normozoospermia	61.37 (+)	54.55 (−)	56.80	60.87 (+)	<0.0001	0.038
Hypospermia (volume <1.5 ml)	9.37 (−)	9.79 (−)	12.48	14.16 (+)	<0.0001	0.139
Oligozoospermia (concentration <15 × 106/ml)	17.08 (+)	14.37	13.43	12.42 (−)	<0.0001	−0.126
Total sperm count <40 × 106	17.33 (+)	15.65	14.59	14.01 (−)	<0.0001	−0.105
Asthenozoospermia (progressive motility <32%)	19.11	20.57	19.59	20.67	0.1483	−0.001
Total motile sperm count <12.5 × 106	2.63 (+)	1.72	1.88	1.67	0.0063	−0.127
Teratozoospermia (normalmorphology <4%)	26.03 (−)	36.21 (+)	36.00 (+)	30.76 (−)	<0.0001	ns
Viability <58%	2.00 (+)	0.79	0.99	0.66 (−)	<0.0001	−0.361
HOST <58%	6.11 (+)	2.99	1.60 (−)	1.98 (−)	<0.0001	−0.433

Males included in this study (n=23,130) were members of couples undergoing fertility evaluation at the Andrology and Reproduction Laboratory in Cordoba, Argentina, from January 2001 to December 2020 (divided into four quinquenniums). Values are expressed as the percentage of patients per quinquennium that yielded values under the normal range for each parameter, according to WHO 2010. Results in bold are those that were statistically significant, identifying also those that were higher (+) or lower (−) than expected under independence, using standardized residual according to Agresti [40]. Statistics: chi-squared independence test and logistic regression (adjusted by age and days of abstinence)

Table 3 shows the percentages of patients per quinquennium that were exposed to each one of the possible causal factors considered in this study. The table shows that the prevalence of parotitis after 13 years of age decreased over time. However, the frequency of middle/heavy tobacco consumers (1–10 cigarettes/day and more than 10 cigarettes/day respectively), patients with higher BMI (i.e., obese and morbidly obese), and those exposed to heat/toxics increased. Furthermore, the frequency of patients that were abstemious decreased over time, while those who drank 1–2 glasses/day increased.

Table 3.

Frequency of patients exposed to each one of the possible causal genitourinary/lifestyle factors evaluated in this study, divided per quinquennium

		Varicocele					Parotitis	Alcohol consumption			Tobacco consumption			BMI category					Heat/toxic exposure
		0	G1	G2	G3	SR		0	1–2	≥3	0	1–10	>10	UW	NW	OW	O	MOB
Quinquennium	1	78.98	10.00	1.87	2.13 (+)	7.02	1.68 (+)	86.25 (+)	11.52 (−)	2.22 (+)	83.84 (+)	12.92 (−)	3.24	–	–	–	–	–	2.16 (−)
	2	76.79	11.65	1.75	1.66	8.15	1.13 (+)	85.91 (+)	13.22 (−)	0.87	83.16 (+)	14.52 (−)	2.32 (−)	0.40	31.46 (+)	49.95	17.13 (−)	1.07	8.30 (−)
	3	78.73	11.14	1.61	1.12 (−)	7.40	0.28 (−)	57.47 (−)	41.55 (+)	0.99	75.23 (−)	23.49((+)	1.28 (−)	0.23	28.56	49.02	20.95	1.24	11.76 (+)
	4	78.88	10.41	1.94	1.64	7.13	0.74	50.69 (−)	48.34 (+)	0.96	78.32	17.04	4.64 (+)	0.24	28.97	47.56	21.58 (+)	1.64 (+)	11.55 (+)

Males included in this study (n=23,130) were members of couples undergoing fertility evaluation at the Andrology and Reproduction Laboratory in Cordoba, Argentina, from January 2001 to December 2020 (divided into four quinquenniums). Results in bold show statistical significance, identifying also those that were higher (+) or lower (−) than expected under independence, using standardized residual according to Agresti [40]. Statistics: chi-squared independence test and logistic regression (adjusted by age and days of abstinence). Varicocele status was categorized as 0 (no varicocele), grades 1, 2, or 3 (G1 to G3), and surgically resolved (SR). Heat/toxic exposure: occupational exposure to heat, pesticides, or radiations. Parotitis: after 13 years of age. Alcohol consumption was quantified as glasses/day and tobacco consumption as cigarettes/day. Body mass index (BMI) categories: underweight (UW; BMI <18.5 kg/m²), normal weight (NW; BMI 18.5–24.9 kg/m²), overweight (OW; BMI 25–29.9 kg/m²), obese (OB; BMI 30–39.9 kg/m²), and morbidly obese (MOB; BMI ≥40 kg/m²)

Table 4 summarizes the associations between the prevalence of abnormalities in seminal parameters and the risk factors that might explain these abnormalities. Suffering parotitis after 13 years of age was associated with increased frequency of oligozoospermia, asthenozoospermia, and OAT. The frequency of abnormalities in TMSC in association with parotitis increased as well. Similarly, having varicocele of any degree (including SR) was significantly associated with oligozoospermia, and varicocele grades 1 and/or 3 in addition to SR were also associated with increased frequency in asthenozoospermia, teratozoospermia, and OAT and decreased frequency in normozoospermia. Moderate alcohol intake was associated with a low prevalence of oligozoospermia, teratozoospermia, and OAT and abnormalities in TMSC. Interestingly, being abstemious was associated with a high prevalence of oligozoospermia. No associations were found between heavy alcohol consumption and semen abnormalities, possibly because of the small number of patients that reported this kind of intake (see “Discussion”). Heavy smoking (>10 cigarettes/day) was associated with abnormalities in sperm motility, and occupational exposure to heat/toxics was related to increased frequency of oligozoospermia, teratozoospermia, and OAT. Finally, morbid obesity was associated with a high prevalence of all abnormalities and with a decrease in normozoospermia. Of note, abnormalities in rapid progressive motility were significantly associated with suffering varicocele (G1 and SR) or parotitis after 13 years of age, consuming >10 cigarettes/day, being abstemious, or drinking 1–2 glasses/day, heat/toxic exposition, and being morbidly obese.

Table 4.

Associations between abnormalities in seminal parameters and genitourinary/lifestyle factors that might explain these abnormalities, indicated as percentages of patients that were exposed to each risk factor and had abnormal results for each sperm parameter

Risk factor		Oligozoospermia	Astenozoospermia	TMSC <12.4 × 106	Teratozoospermia	Normozoospermia	OAT
Parotitis	≤13	13.77	20.02	1.81	33.06	58.19	7.12
	>13	22.99 (+)	30.48 (+)	5.88 (+)	32.62	53.48	13.37 (+)
Varicocele	0	12.49 (−)	18.86 (−)	1.77	31.85 (−)	59.74 (+)	6.46 (−)
	G1	16.72 (+)	23.89 (+)	2.11	37.75 (+)	52.57 (−)	8.64 (+)
	G2	17.68 (+)	22.03	1.94	34.62	56.90	8.96
	G3	19.27 (+)	25.14 (+)	3.07	32.96	57.54	10.34 (+)
	SR	21.49 (+)	26.14 (+)	2.44	37.91 (+)	50.70 (−)	10.94 (+)
Alcohol consumption	0	14.33 (+)	20.30	2.00	32.75	57.95	7.24
	1–2	12.06 (−)	18.88	1.29 (−)	30.21 (−)	61.66 (+)	6.18 (−)
	≥3	18.11	20.99	3.29	37.45	54.73	9.05
Tobacco consumption	0	13.72	20.12	1.82	32.39	58.69	6.92
	1–10	12.97	18.22	1.61	30.31	60.97	6.62
	>10	14.63	23.69 (+)	1.59	30.89	58.66	8.43
BMI categories	UW	16.67	22.92	2.08	41.67	47.92	6.25
	NW	12.48	18.17 (−)	1.55	33.10	59.36	6.36
	OW	12.60	19.78	1.65	32.14	59.78	6.88
	O	13.82	21.23 (+)	1.63	33.07	58.16	7.19
	MO	26.14 (+)	32.37 (+)	4.96 (+)	41.91 (+)	50.41 (−)	16.94 (+)
Heat/toxic exposure	No	13.38	19.57	1.76	31.58	59.49	6.68
	Yes	16.06 (+)	21.32	1.83	34.03 (+)	57.64	9.25 (+)

Males included in this study (n=23,130) were members of couples undergoing fertility evaluation at the Andrology and Reproduction Laboratory in Cordoba, Argentina, from January 2001 to December 2020. Results in bold are those that were statistically significant, identifying also those that were higher (+) or lower (−) than expected under independence, using standardized residual according to Agresti [40]. Statistics: chi-squared independence test and logistic regression (adjusted by age and days of abstinence). TMSC total motile sperm count. OAT oligo-astheno-teratozoospermia. Heat/toxic exposure: occupational exposure to heat, pesticides, or radiations. Parotitis: after 13 years of age. Varicocele status was categorized as 0 (no varicocele), grades 1, 2, or 3 (G1 to G3), and surgically resolved (SR). Alcohol consumption was quantified as glasses/day and tobacco consumption as cigarettes/day. Body mass index (BMI) categories: underweight (UW; BMI <18.5 kg/m²), normal weight (NW; BMI 18.5–24.9 kg/m²), overweight (OW; BMI 25–29.9 kg/m²), obese (OB; BMI 30–39.9 kg/m²), and morbidly obese (MOB; BMI ≥40 kg/m²)

Discussion

In this study, we sought to evaluate the variations in the seminal quality of 23,130 patients attending an andrology center in Córdoba, Argentina, over the last 20 years, and to identify possible causal genitourinary and/or lifestyle factors, analyzing also the prevalence of these risk factors over time and the associations between them and semen abnormalities. To the best of our knowledge, this work is among the few that assess the prevalence of risk factors in comparison with semen quality [41, 42], and the first one performed in South America.

Broadly, it can be assumed that the population included in our study did not show an important decrease in seminal quality over the last 20 years. Beyond a decrease in normozoospermia in Q2, possibly explained by an increase in teratozoospermia, other important parameters of the spermogram did not change. In fact, abnormalities in sperm concentration (oligozoospermia), total sperm count, viability, and response to the hypoosmotic test showed a decreasing trend over time. Other studies assessing sperm quality among infertile couples reached similar conclusions [12–14, 19, 43, 44]. On the other hand, we could establish significant associations between sperm abnormalities and risk factors, some of which showed increasing prevalence values during the study period. It is important to keep in mind that these factors might act separately but also synergically, as published in previous studies [29].

As mentioned before, teratozoospermia was the main sperm abnormality that transitoriously increased during the study period (in Q2 and Q3). This pattern was associated with varicocele G1 and SR, morbid obesity, and exposure to heat/toxics, factors that have been previously linked to sperm morphology impairment [30, 45, 46]. Of note, the prevalence of exposure to heat/toxics and morbid obesity increased over the last 20 years, as well. In this regard, Sengupta et al. [24] pointed out that agricultural areas of South America are “cursed” by exposure to organochloride pesticides and other endocrine disruptors, which might be more detrimental to fertility in the coming years. On the other hand, between 1975 and 2016, the worldwide prevalence of obesity nearly tripled, and continues to rise in low- and middle-income countries [47].

With respect to previous studies, while several authors have reported a decrease in the percentage of normal morphology [7, 10, 18, 48], others report either increases or no changes [16, 43]. Nevertheless, it has been mentioned that the assessment of this parameter is highly dependent on the classification criteria used and the evaluation experience of the laboratory staff [49, 50]; hence, in some studies, sperm morphology was not evaluated due to high inter-observer variation [51–53]. Therefore, conflicting findings regarding sperm morphology trends must be interpreted in light of these considerations. Nevertheless, a strength of our study is that in our andrology center, this parameter has been evaluated by strict criteria since its opening, always by the same two trained technicians.

As an additional comment, it is worth mentioning that not only patients’ intrinsic factors (such as health and lifestyle) can influence sperm quality, but also extrinsic factors such as climate and pollution. We are currently developing a study on the effects of climate and annual temperature variations on sperm quality over the last 20 years. Strikingly, the two quinquenniums with the highest teratozoospermia rates (Q2 and Q3) coincide with average temperatures above the 20-year media. Since in the current context of climate change, the possible effects of meteorological variables on gamete quality must be thoroughly analyzed, we are developing this new study independently of the present one.

Although in our population the prevalence of asthenozoospermia did not change over time, it was associated with suffering varicocele (G1, G3, or SR) or parotitis after 13 years of age, excessive amounts of tobacco (>10 cigarettes/day), obesity, and morbid obesity. Such risk factors are well known as pro-inflammatory agents and consequently oxidative stress promoters [54–57]. Sperm motility appears to be particularly vulnerable to oxidative stress [58]. Concordantly, previous reports alert about the negative impact of these risk factors on sperm motility [29, 30, 46, 55, 59]. Furthermore, it is widely accepted that the effective passage of spermatozoa through cervical mucus depends on rapid progressive motility [60]. Eliasson stated that ignoring the speed of progressive motility is like ignoring a very important prognostic fertility factor [44]. Therefore, we calculated the prevalence of abnormalities in this parameter (defining the lower normal limit according to previous publications) and found an increasing pattern over time. Moreover, all the risk factors evaluated in this study showed to be significantly associated with its high prevalence.

In addition to the sperm parameters included in the WHO laboratory manual and as a complement to the analysis on sperm motility, we also analyzed the TMSC, which had been previously reported to have a better correlation with male factor infertility [61, 62]. We did not find any changes in the prevalence of abnormalities in this parameter, probably because of a decreased trend in oligozoospermia and total sperm count below the normal range (discussed below). Suffering parotitis after 13 years of age or being morbidly obese was associated with having TMSC below the reference value, probably because of the previously mentioned association between motility and oxidative stress.

Sperm concentration and/or total sperm count have been claimed by several authors as showing a downward trend over the years [2, 9–11] and these results have reverberated even in public discussions [63, 64], raising the alarms about a threatened status of male fertility. However, these results face opposing reports from other authors, who did not find such negative trends [15, 16, 65–67].

In our study, we found a significant decrease in the prevalence of oligozoospermia, and although we found an increase in the prevalence of hypospermia, the percentage of patients with abnormal total sperm count decreased as well. In agreement with previous reports [30, 41, 68–70], we found an association between oligozoospermia and parotitis, all grades of varicocele including SR, exposure to heat/toxics, and morbid obesity; the last ones showed increasing prevalence along the studied period. Noteworthy, moderate alcohol consumption (i.e., 1–2 glasses per day) that increased over time was associated with a low prevalence of oligozoospermia, while being abstemious was associated with an increase of this abnormality. This agrees with previous reports [29, 71], in which a U- or J-shaped relationship between alcohol consumption and semen quality was observed, with low-moderate intake being protective with respect to abstention or abusive drinking. It is important to highlight that since this was a retrospective study, the only information available was the number of glasses of alcohol consumed per day, without specification about the type of beverage; for this reason, it was impossible for us to measure alcohol consumption as grams of alcohol/day or units of alcohol/day. Although this measure (glasses/day or drinks/day) has been previously used in other studies [28, 29], the impossibility to strictly calculate the daily dose of alcohol is an important limitation. Besides, we did not find a negative association between heavy drinking and oligozoospermia or any other semen abnormality evaluated. It is important to remark that among the patients evaluated in this study, less than 1% reported alcohol consumption of 3 or more glasses/day. Furthermore, approximately 90% of these patients consumed 3, 4, or 5 glasses per day, which some authors still consider a moderate alcohol intake [72, 73]. Thus, we could not certainly analyze a possible association between heavy drinking and sperm abnormalities, although detrimental effects of heavy alcohol consumption on sperm quality have been reported [74, 75].

Finally, in our study, we found a decrease in the prevalence of abnormalities in terms of sperm viability and sperm response to the hypoosmotic test.

Overall, the patients included in this study did not show a clear trend of impairment in seminal quality during the last 20 years. We only found an increasing pattern of abnormalities in hypospermia and rapid progressive motility below the limit, and a transient increasing pattern in teratozoospermia paralleled with a decrease in normozoospermia. Conversely, some parameters like sperm concentration, total sperm count, viability, and response to the hypoosmotic test showed an improvement over time, since the prevalence of values under the normal range decreased. Moreover, we were able to detect changes in the frequency of lifestyle factors, as well as associations between them and semen abnormalities. The fact that two or more risk factors could have synergistic rather than additive effects on male fertility adds complexity to this matter.

Our results contrast with a number of studies that report a decline in sperm quality over time [7, 10, 11]. However, some authors have reported that irrespective of the observed downward trend in seminal quality, it was not associated with a decrease in fertility potential [76]. Moreover, the idea that a decline in sperm count provokes a decay in male fertility and health has been recently questioned by Boulicault et al. [2021], who proposed an alternative interpretation in which sperm count varies within a wide range, much of which can be considered non-pathological and species-typical. This new paradigm offers tools for the re-analysis of existing epidemiological data and design, analysis and interpretation of future studies on sperm count, environment, and men’s health [77].

Finally, this study is certainly not devoid of limitations. First of all, since it was a retrospective analysis, we were unable to determine a clear cause-effect relationship between the variables. Secondly, as in other studies [71, 73, 78, 79], since information on exposition to risk factors was voluntarily provided by the patients, it might have some bias. Third, the study of men attending a fertility clinic precludes any prediction about the general population. Fourth, since the Andrology and Reproduction Laboratory is a private institution, patients without social welfare or with very low economic resources do not attend this laboratory. Nevertheless, despite these limitations, this study performed on a large number of patients attending a single fertility center during a 20-year period contributes to the almost inexistent database concerning semen quality trends in South America, and Argentina in particular.

Accurate knowledge of the rates of infertility causes and their trends over time is essential for national health agencies. Furthermore, since some of these risk factors are modifiable (alcohol and tobacco consumption, body weight, or exposure to heat/toxics), clinicians should provide greater awareness on such fertility-threatening lifestyles. Future prospective and multicenter studies, including representative samples of the general population in which both conventional and biofunctional semen parameters (e.g., mitochondrial function or DNA fragmentation) are analyzed, become necessary to confirm whether semen quality is really declining and, what is more important, to recognize if this decline in sperm quality is actually associated with fertility status in men.

Author contribution

Conception and design of the study: Ramírez, Molina, Mangeaud, and Martini; acquisition and registration of the data: Tissera, Gaggino, and Molina; analysis and interpretation of the data: Ramírez, Mangeaud, and Martini; drafting the article: Ramírez and Martini; critical revision of the article: all the authors; approval of the currently submitted version: all the authors; agree both to be personally accountable for the authors’ own contributions and to ensure that questions are related to the accuracy or integrity of any part of the work: all the authors.

Data availability

The datasets used and/or analyzed during the study are available from the corresponding author on reasonable request.

Code availability

Not applicable

Declarations

Ethical approval

Since this study included non-invasive procedures and semen samples were voluntarily provided by patients and kept rigorously anonymous, approval by an institutional review board was not mandatory. Principles outlined in the Declaration of Helsinki regarding human experimentation were met. Furthermore, the andrology laboratory and the research institute, as well as their head researchers, are certified by the local authority committee (Consejo de Evaluación Ética de Investigación en Salud, COEIS; and Registro Provincial de Investigación en Salud, RePis), corresponding to Center numbers122 and 109, respectively, and researcher numbers 501 and 1055, respectively.

Consent to participate

All the patients included in this study signed written informed consent allowing the use of their data for statistical and scientific purposes.

Consent for publication

All the authors have seen and agree with the submitted version of this manuscript and consent to its publication.

Conflict of interest

The authors declare no competing interests.