Epidemiologic methods for investigating male fecundity

Clusterin expression and distribution in spermatozoa as predictor of male fertility

Clusterin (CLU), one of the main glycoproteins in mammalian semen and the male reproductive tract, plays a role in spermatogenesis and sperm maturation. Given the poor reliability of classic seminal studies in determining male-fertilizing capacity and the differences in CLU abundance between normal and abnormal spermatozoa, we investigated the potential value of mRNA-CLU levels and protein distribution in spermatozoa as markers of sperm quality and predictors of male fertility. This multicenter study included 90 patients undergoing in vitro fertilization (IVF) treatment with their partners, and a control group of 36 fertile males with normal seminograms. We assessed the relationship between IVF treatment outcomes, seminogram variables, mRNA-CLU levels by quantitative real-time-PCR and CLU distribution by immunostaining in spermatozoa. Our study reveals CLU staining in the acrosome (p = 0.002, OR 14.8, 95% CI: 2.7-79.3) and mRNA-CLU levels (p = 0.005, OR 10.85, 95% CI: 2.0-57.4) as independent risk factors for pregnancy failure, irrespective of traditional seminogram variables. Additionally, our results suggest that CLU, and specially its secreted isoform, constitutes a component of the protein pool that human spermatozoa can produce during its maturation process, exhibiting a variable abundance and distribution in spermatozoa from fertile men compared to those in patients with altered seminograms and infertile patients with normal seminograms. Our study is the first to identify mRNA-CLU levels and CLU immunostaining in the spermatozoa acrosome as independent risk factors for pregnancy failure, with distribution patterns correlating with sperm maturity and seminogram alterations.

Assessing and Screening of Female Fertility in Artificially Bred Asian Yellow Pond Turtles (Mauremys mutica) Based on Parentage Assignment

The Asian yellow pond turtle (Mauremys mutica) is widely traded in China, and its artificial breeding has now become a major industry. However, the insufficient offspring supply and reproductive decline of farmed turtles make the wild turtles more vulnerable. The present study was mainly designed to quantify the fecundity of M. mutica and attempt to screen for good reproductive performance in females. The genetic variability of the population and its genetic structure were also analysed. The parent-offspring relationships of all offspring in four consecutive years were confirmed using sixteen microsatellite loci. The genetic variability between the parents and offspring was low, and offspring of different years also showed little variability. We summarised the reproductive results of all females and counted the annual number of offspring and the variation in the number of offspring. The females were then divided into three types (stable, undulating and levelling off) according to the continuity. We selected seven females with good reproductive ability, which provided 16.94% of the annual contributions, while there were two females that had no offspring in four years. We also analysed the possible reasons for this difference and the importance of carrying out a family survey. This research can provide the basis and materials for the creation of a good reproductive group and the study of the reproductive biology of turtles in M. mutica aquaculture.

Minor impact on fertility in men with inflammatory bowel disease: A National Cohort Study from Sweden

BACKGROUND AND AIMS

Onset of inflammatory bowel disease (IBD) in men is most common during childbearing age, but little is known about the impact on fertility. Previous studies of fertility in men were small, which justifies this large nation-based registry study.

METHODS

Fertility was assessed in a national cohort of men with IBD aged 15-44 years in 1964-2014, identified from the Swedish National Patient Register, and in a reference cohort matched for age and place of residence (ratio 1:5). Information about childbirths was found in the Swedish Multi-Generation Register. Patients with indeterminate colitis or inconsistent IBD coding were classified as IBD-unclassified (IBD-U).

RESULTS

The cohorts included 29,104 men with IBD and 140,901 matched individuals. IBD patients had a lower fertility rate (number of births per 1000 person years) compared with the matched individuals; 1.28 (SD 1.27) versus 1.35 (SD 1.31; p < 0.001). Fertility was somewhat impaired in all IBD subtypes compared with the matched cohort; ulcerative colitis (UC) (hazard ratio [HR] 0.93, 95% CI 0.91-0.96), Crohn's disease (CD) (HR 0.95, 95% CI 0.92-0.98) and IBD-U 0.92, 95% CI 0.89-0.95. The cumulated total parity and the parity progression were also decreased for all IBD subtypes. Within the IBD cohort disease severity, intensity of medical treatment (CD) and bowel surgery (IBD-U) were further associated with impaired fertility.

CONCLUSIONS

This nationwide cohort study shows only slightly impaired fertility in men with IBD.

Environmental Exposure to Triclosan and Male Fecundity: A Prospective Study in China

Triclosan (2,4,4′-trichloro-2′-hydroxy-diphenyl ether, TCS) is widely used in personal care and household products. It is ubiquitous across the ecosystem nowadays. Several in vitro and in vivo studies have suggested the possible adverse effects of TCS on male reproductive health. However, little research has been done on human beings, especially in eastern countries. To assess the effects of TCS exposure on male fecundity, we recruited couples who planned to conceive and went to the preconception care clinics for physical examination in Shanghai, China. TCS was quantified in male urine samples collected at enrollment. For this study, 443 couples were included in the cohort, and 74.7% of couples (n = 331) were prospectively followed 12 months later. The outcomes of interest included the pregnancy status of their wives and time to pregnancy. Elevated male urinary TCS concentrations were found to be associated with diminished fecundability (fecundability odds ratio (FOR) 0.77; 95% CI, 0.62–0.97). The risk of infertility significantly increased (OR = 1.6; 95% CI, 1–2.6) as TCS levels elevated. Besides, we divided TCS concentration into tertiles a priori, and there tended to be a dose-response pattern in both analyses. Our findings suggest that environmental exposure to TCS may have an adverse impact on male fecundity.

Temporal trends in semen concentration and count among 327 373 Chinese healthy men from 1981 to 2019: a systematic review

STUDY QUESTION

Are there temporal trends of sperm concentration (SC) and total sperm count (TSC) in Chinese healthy males from 1981 to 2019?

SUMMARY ANSWER

Our result indicated a temporal decrease in SC and TSC among 327 373 healthy Chinese men in the recent four decades.

WHAT IS KNOWN ALREADY

A review of 61 papers reported a temporal decline in SC and TSC from 1938 to 1990. This trend was later confirmed by a systematic review of 185 published papers from 1981 to 2013. However, the majority of the included individuals were from western countries. In China, whether SC and TSC have declined remains controversial.

STUDY DESIGN, SIZE, DURATION

This systematic review of published articles used data extracted from Pubmed, Science Direct, Embase, China-National-Knowledge-Infrastructure (CNKI) and Wanfang Data to assess changes in SC and TSC in China from 1981 to 2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 111 studies including 327 373 individuals who provided semen samples from 1981 to 2019 were extracted for the present analysis. Study selection and data extraction were performed by two independent researchers. The trends in SC and TSC were analysed using liner-regression and meta-regression before and after adjusting for potential covariates. Moreover, subgroups, categorised based on geographic region, fertility status or recruitment source, were also analysed.

MAIN RESULTS AND THE ROLE OF CHANCE

SC declined significantly (slope liner-regression = -0.748 million/ml/year; P = 0.005; slope meta-regression = -0.824 million/ml/year; P < 0.001) between 1981 and 2019 in China. Trends for TSC was similar to that for SC (slope liner-regression = -2.073 million/year; P = 0.032; slope meta-regression = -2.188 million/year; P = 0.003). In subgroup meta-regression analyses, males with definite fertility had continuous declines in SC (slope northern group=-2.268, P = 0.009; slope southern group=-1.014, P = 0.009) and TSC (slope northern group=-9.675, P = 0.010; slope southern group=-3.215, P = 0.042). However, in the unselected group, where fertility status was unknown, the obvious downward trend in SC was only seen in males from Northern regions (slope = -0.836, P = 0.003). Another subgroup analysis demonstrated that obvious decreases in SC (slope = -1.432, P < 0.001) and TSC (slope=-4.315, P = 0.001) were only seen in volunteer groups but not in pre-pregnancy examination groups and other recruitment groups. The results changed minimally in multiple sensitivity analyses.

LIMITATIONS, REASONS FOR CAUTION

The validity of the meta-analysis results was limited mainly by the quality of the included studies. Additionally, our study spanned many decades and the recommended criteria for some semen parameter assessments have significantly changed, which may bring about some unavoidable bias. Moreover, the data remain insufficient especially in some provinces of China.

WIDER IMPLICATIONS OF THE FINDINGS

The present study is the first study to report significant decreases in SC and TSC in 327 373 healthy Chinese men between 1981 and 2019, indicating a serious reproductive health warning. Further studies on the causes of the declines are urgently needed.

STUDY FUNDING/COMPETING INTEREST(S)

D.Z. is supported by the National Natural Science Funding of China, Natural Science Funding of Shaanxi Province, Science Funding of Health Department, Shaanxi Province, Fundamental Research Funds for the Central University and the Project of Independent Innovative Experiment for Postgraduates in Medicine in Xi'an Jiaotong University. The authors have no conflicts of interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Fertility in men with hypospadias: A nationwide register-based study using dizygotic twinning rates as an indicator of semen quality

BACKGROUND

It is not known if impaired fertility in men with hypospadias is caused by decreased semen quality or other factors. Semen quality in men born with hypospadias may be impaired due to effects of androgens or testicular dysgenesis but has been very little studied.

OBJECTIVES

To study semen quality in men with hypospadias using dizygotic twinning rates as an epidemiological indicator. We further aimed to study men treated for cryptorchidism, given a hypothesized mutual etiology for decreased semen quality.

MATERIALS AND METHODS

We conducted a population-based study using national Swedish registers. A total of 4,363,165 births between 1964 and 2013 were included. The association between hypospadias and cryptorchidism, and fathering dizygotic multiple births was estimated using logistic regression and presented as odds ratios. The main analyses excluded births conceived using assisted reproductive technology (ART).

RESULTS

We identified a total of 5317 births with fathers with hypospadias, including 26 dizygotic births conceived unassisted. No significant association was found between hypospadias and dizygotic twinning (OR 1.10, 0.75-1.61). We estimated a significantly increased odds for dizygotic multiple births in men treated for cryptorchidism (OR 1.35, 1.01-1.81) which was decreased after exclusion of ART, but the estimate was not significant (OR 0.75, 0.48-1.18).

DISCUSSION

Using dizygotic twinning rates as an indicator of semen quality, we did not find any difference between fathers with hypospadias and controls. Due to sample size, we could not analyze phenotypes separately and can therefore not exclude impaired semen quality in severe hypospadias. We could not demonstrate any association between dizygotic twinning and cryptorchidism. Men treated for cryptorchidism were more likely than controls to use ART to conceive.

CONCLUSION

Men with hypospadias who conceived without ART were not shown to have impaired semen quality using dizygotic twinning as an epidemiological indicator.

SNP's in xenobiotic metabolism and male infertility

1. Glutathione S-transferases (GST) and cytochrome P450s (CYPs) are xenobiotic metabolizing enzymes participating in the protection of cell. The present study aimed to investigate the relationship between polymorphisms of glutathione S-transferase M1 (GSTM1) null, glutathione S-transferase T1 (GSTT1) null, glutathione S-transferase P1 (GSTP1) Ile105Val, cytochrome P450 1A2 (CYP1A2) 734 C→A, cytochrome P450 2D6 (CYP2D6) 1934 G→A and male infertility.2. A total of 306 azoospermic or oligozoospermic infertile men and 129 normozoospermic or fertile controls were enrolled in the study. Multiplex polymerase chain reaction (PCR) or PCR-restriction fragment length polymorphism methods were used for genotyping. There was a significant relationship between male infertility and CYP2D6 GG genotype (p < 0.001). CYP1A2 AA genotype was slightly higher in the infertile group (p = 0.056).3. There was no association between GSTT1 null polymorphisms and male infertility (p = 0.068), GSTM1 null (p = 0.843) and GSTP1 Ile105Val (p = 0.192) genes. GSTM1 null genotype frequency was higher in azoospermic men (p = 0.009). Men carrying CYP1A2 AA genotype had higher risk of infertility risk (OR = 3.14; %95 CI = 1.16-8.54) in the smoker group.4. Our results demonstrated that polymorphisms of CYP2D6 and CYP1A2 may play a role in idiopathic male infertility in our sample population.

Exposure to non-persistent chemicals in consumer products and fecundability: a systematic review

BACKGROUND

Exposure to non-persistent chemicals in consumer products is ubiquitous and associated with endocrine-disrupting effects. These effects have been linked to infertility and adverse pregnancy outcomes in some studies and could affect couple fecundability, i.e. the capacity to conceive a pregnancy, quantified as time to pregnancy (TTP).

OBJECTIVE AND RATIONALE

Few epidemiologic studies have examined the impact of non-persistent chemicals specifically on TTP, and the results of these studies have not been synthesized. We undertook a systematic review to summarize the strength of evidence for associations of common non-persistent chemicals with couple fecundability and to identify gaps and limitations in the literature, with the aim of informing policy decisions and future research.

SEARCH METHODS

We performed an electronic search of English language literature published between 1 January 2007 and 25 August 2017 in MEDLINE, EMBASE.com, Global Health, DART/TOXLINE, POPLINE and DESTAF. We included human retrospective and prospective cohort, cross-sectional and case-control studies that examined phthalates, bisphenol A, triclosan, triclocarban, benzophenones, parabens and glycol ethers in consumer products, and considered TTP or fecundability as an outcome among women, men and couples conceiving without medical assistance. We excluded editorials, opinion pieces, introductions to special sections, articles that described only lifestyle (e.g. caffeine, stress) or clinical factors (e.g. semen parameters, IVF success). Standardized forms for screening, data extraction and study quality were developed using DistillerSR software and completed in duplicate. We used the Newcastle-Ottawa Scale to assess risk of bias and devised additional quality metrics based on specific methodological features of fecundability studies.

OUTCOMES

The search returned 3456 articles. There were 15 papers from 12 studies which met inclusion criteria, of which eight included biomarkers of chemical exposure. Studies varied widely in terms of exposure characterization, precluding a meta-analytic approach. Among the studies that measured exposure using biospecimens, results were equivocal for associations between either male or female phthalate exposure and TTP. There was preliminary support for associations of female exposure to some parabens and glycol ethers and of male exposure to benzophenone with longer TTP, but further research and replication of these results are needed. The results provided little to no indication that bisphenol A, triclocarban or triclosan exposure was associated with TTP.

WIDER IMPLICATIONS

Despite a growing literature on couple exposure to non-persistent endocrine-disrupting chemicals and fecundability, evidence for associations between biologically measured exposures and TTP is limited. Equivocal results with different non-persistent chemical compounds and metabolites complicate the interpretation of our findings with respect to TTP, but do not preclude action, given the documented endocrine disrupting effects on other reproductive outcomes as well as fetal development. We therefore advocate for common-sense lifestyle changes in which both females and males seeking to conceive minimize their exposure to non-persistent chemicals.

SYSTEMATIC REVIEW REGISTRATION NUMBER

CRD42018084304.

Is human fecundity changing? A discussion of research and data gaps precluding us from having an answer

Fecundity, the biologic capacity to reproduce, is essential for the health of individuals and is, therefore, fundamental for understanding human health at the population level. Given the absence of a population (bio)marker, fecundity is assessed indirectly by various individual-based (e.g. semen quality, ovulation) or couple-based (e.g. time-to-pregnancy) endpoints. Population monitoring of fecundity is challenging, and often defaults to relying on rates of births (fertility) or adverse outcomes such as genitourinary malformations and reproductive site cancers. In light of reported declines in semen quality and fertility rates in some global regions among other changes, the question as to whether human fecundity is changing needs investigation. We review existing data and novel methodological approaches aimed at answering this question from a transdisciplinary perspective. The existing literature is insufficient for answering this question; we provide an overview of currently available resources and novel methods suitable for delineating temporal patterns in human fecundity in future research.

Evaluation of reference values of standard semen parameters in fertile Egyptian men

The reference values of human semen, published in the WHO's latest edition in 2010, were lower than those previously reported. The objective of this study was to evaluate reference values of standard semen parameters in fertile Egyptian men. This cross-sectional study included 240 fertile men. Men were considered fertile when their wives had recent spontaneous pregnancies with time to pregnancy (TTP) ≤12 months. The mean age of fertile men was 33.8 ± 0.5 years (range 20-55 years). The 5th percentiles (95% confidence interval) of macroscopic semen parameters were 1.5 ml for volume and 7.2 for pH. The 5th percentiles of microscopic parameters were 15 million/ml for sperm concentration, 30 million per ejaculate for total sperm count, 50% for total motility, 40% for progressive motility, 62% for vitality, 4% for normal sperm forms and 0.1 million/ml for seminal leucocyte counts. In conclusion, fertile Egyptian men had higher reference values of sperm total motility, progressive motility and vitality, and lower reference values for total sperm counts as compared to those determined by the latest edition of the WHO laboratory manual in 2010. Other semen parameters were identical to those defined by the WHO 2010 manual.

The reference values for semen parameters of 1213 fertile men in Guangdong Province in China

Semen samples were collected from 1213 fertile men whose partners had a time-to-pregnancy (TTP) ≤12 months in Guangdong Province in Southern China, and semen parameters including semen volume, sperm concentration, total counts, motility, and morphology were evaluated according to the World Health Organization (WHO) 2010 guideline. All semen parameters analyzed were normal in ~62.2% of the total samples, whereas ~37.8% showed at least one of the semen parameters below normal threshold values. The fifth centiles (with 95% confidence intervals) were 1.3 (1.2–1.5) ml for semen volume, 20 × 10⁶ (18×10⁶–20×10⁶) ml⁻¹ for sperm concentration, 40 × 10⁶ (38×10⁶–44×10⁶) per ejaculate for total sperm counts, 48% (47%–53%) for vitality, 39% (36%–43%) for total motility, 25% (23%–27%) for sperm progressive motility, 5.0% (4%–5%) for normal morphology. The pH values ranged from 7.2 to 8.0 with the mean ± standard deviation at 7.32 ± 0.17. No effects of age and body mass index were found on semen parameters. Occupation, smoking and alcohol abuse, varicocele appeared to decrease semen quality. Sperm concentration, but not sperm morphology, is positively correlated with TTP, whereas vitality is negatively correlated with TTP. Our study provides the latest reference values for the semen parameters of Chinese fertile men in Guangdong Province, which are close to those described in the new WHO guidelines (5^th Edition).