Increasing trends in childlessness in recent birth cohorts - a registry-based study of the total Danish male population born from 1945 to 1980

Concurrent decline in teenage fertility rate and binge drinking? An observational study across 45 nations

INTRODUCTION

Alcohol consumption is associated with unintended pregnancies among teenagers. Its role as a broader determinant of teenage fertility rates remains unclear. We investigate whether adolescent binge drinking affects the number of teenage births.

METHODS

Binge drinking data from 137,898 females aged 15-16 were collected in the HBSC study (2002-2018, 43 countries/regions) and 267,359 in the ESPAD study (1995-2019, 41 countries/regions). Age-specific fertility rates were from the Human Fertility Database and the World Health Organization. We examined changes over time in countries' average levels of binge drinking among female pupils aged 15-16 and population-level fertility rates for the same cohorts when aged 16-19 years.

RESULTS

Controlling for differences between countries and survey waves, we found an association between binge drinking and fertility rate, B = 0.019, 95% confidence interval [0.004, 0.034]. When accounting for the countries' time trends, the association was substantially reduced, B = 0.006, 95% confidence interval [-0.0062, 0.0174]. The relationship was not moderated by abortion rates and controlling for contraceptive use had no impact on the findings.

DISCUSSION AND CONCLUSIONS

The association between adolescent binge drinking and fertility rates diminishes when accounting for country-specific time trends. Given the lack of clear mechanisms linking binge drinking to trends in fertility rates rather than shorter-term changes, the association likely reflects broader secular trends. Binge drinking may be involved in teen pregnancy and childbirth in individual cases but it does not explain recent developments in teenage fertility rates.

Frequency, morbidity and equity - the case for increased research on male fertility

Currently, most men with infertility cannot be given an aetiology, which reflects a lack of knowledge around gamete production and how it is affected by genetics and the environment. A failure to recognize the burden of male infertility and its potential as a biomarker for systemic illness exists. The absence of such knowledge results in patients generally being treated as a uniform group, for whom the strategy is to bypass the causality using medically assisted reproduction (MAR) techniques. In doing so, opportunities to prevent co-morbidity are missed and the burden of MAR is shifted to the woman. To advance understanding of men's reproductive health, longitudinal and multi-national centres for data and sample collection are essential. Such programmes must enable an integrated view of the consequences of genetics, epigenetics and environmental factors on fertility and offspring health. Definition and possible amelioration of the consequences of MAR for conceived children are needed. Inherent in this statement is the necessity to promote fertility restoration and/or use the least invasive MAR strategy available. To achieve this aim, protocols must be rigorously tested and the move towards personalized medicine encouraged. Equally, education of the public, governments and clinicians on the frequency and consequences of infertility is needed. Health options, including male contraceptives, must be expanded, and the opportunities encompassed in such investment understood. The pressing questions related to male reproductive health, spanning the spectrum of andrology are identified in the Expert Recommendation.

Understanding the sex inequality in childlessness: an approach using Swedish register data

In most countries, men are more likely to be childless than women. Understanding how this inequality arises is important given the significance of parenthood for individuals' lives. The objective of this study was to explore how three prominent explanations for sex inequalities in childlessness relate to the Sex Gap in Childlessness (SGC) in Sweden. The three explanations examined were sex ratio imbalance (more men than women), mismeasurement of fatherhood (inequalities in registration) and partnership differences (inequality in multi-partner fertility). Administrative register data for cohorts born in 1945-1974 were used. The population was restricted to men and women who were born in Sweden or arrived prior to the age of 15, and all registered childbearing partnerships were examined. To explore the possible significance of the three explanations, counter-factual standardization was used. Of the three explanations examined, the population sex ratio had the largest positive impact on the SGC, while multi-partner fertility had a negative impact. The results show that inequalities in the sex ratio can explain about 20-34% of the SGC depending on cohort. Inequalities in registration of fathers explain about 9-24% of the SGC depending on cohort. Finally, results show that women are slightly more likely to have multiple partners, and that this behaviour has a substantial minimizing effect on the SGC (minimizing it by 6-65%). To the authors' knowledge this was the first paper to estimate the scope of the impacts of these three mechanisms on the SGC. Differences in multi-partner fertility have in many instances been used as an explanation for men's higher childlessness. This study shows that women have slightly more childbearing partners than men, and that this actually leads to a smaller SGC in the studied population.

NRF2 loss recapitulates heritable impacts of paternal cigarette smoke exposure

Paternal cigarette smoke (CS) exposure is associated with increased risk of behavioral disorders and cancer in offspring, but the mechanism has not been identified. Here we use mouse models to investigate mechanisms and impacts of paternal CS exposure. We demonstrate that CS exposure induces sperm DNAme changes that are partially corrected within 28 days of removal from CS exposure. Additionally, paternal smoking is associated with changes in prefrontal cortex DNAme and gene expression patterns in offspring. Remarkably, the epigenetic and transcriptional effects of CS exposure that we observed in wild type mice are partially recapitulated in Nrf2-/- mice and their offspring, independent of smoking status. Nrf2 is a central regulator of antioxidant gene transcription, and mice lacking Nrf2 consequently display elevated oxidative stress, suggesting that oxidative stress may underlie CS-induced heritable epigenetic changes. Importantly, paternal sperm DNAme changes do not overlap with DNAme changes measured in offspring prefrontal cortex, indicating that the observed DNAme changes in sperm are not directly inherited. Additionally, the changes in sperm DNAme associated with CS exposure were not observed in sperm of unexposed offspring, suggesting the effects are likely not maintained across multiple generations.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Two simple cleanup methods combined with LC-MS/MS for quantification of steroid hormones in in vivo and in vitro assays

Measuring both progestagens, androgens, corticosteroids as well as estrogens with a single method makes it possible to investigate the effects of endocrine-disrupting chemicals (EDCs) on the main pathways in the mammalian steroidogenesis. This paper presents two simple methods for the determination of the major steroid hormones in biological matrixes using liquid chromatography tandem mass spectrometry (LC-MS(2)). A novel method was developed for the determination of 14 steroids in the H295R in vitro assay without the need for solid phase extraction (SPE) purification prior to LC-MS(2) analysis. The in vitro assay was validated by exposing H295R cells to prochloraz for inhibiting steroid hormone secretion and by exposing cells to forskolin for inducing steroid hormone secretion. The developed method fulfills the recommendations for the H295R assay suggested by the OECD. Furthermore, a simple off-line SPE methodology was developed for the necessary clean-up of in vivo assays. Samples, such as gonad tissue, plasma and serum, are complex biological matrixes, and the SPE methodology was optimized to remove salts and proteins prior to elution of target analytes. At the same time, lipophilic compounds were retained on the SPE cartridge during elution. This, combined with the multi-steroid LC-MS(2) method, made it possible to determine 10 steroids in male Sprague-Dawley rat gonad tissue. Furthermore, it was possible to quantify 6 steroids in the plasma. In general, the observed concentration of steroid hormones in plasma, testes, and H295R cell medium corresponded well with previous studies. The off-line SPE method was validated using spiked charcoal-stripped serum. Method recovery, accuracy, precision and robustness were all good. Instrument sensitivity was in the range of 55-530 pg/mL (LLOQ).

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Possible fetal determinants of male infertility

Although common reproductive problems, such as male infertility and testicular cancer, present in adult life, strong evidence exists that these reproductive disorders might have a fetal origin. The evidence is derived not only from large epidemiological studies that show birth-cohort effects with regard to testicular cancer, levels of testosterone and semen quality, but also from histopathological observations. Many infertile men have histological signs of testicular dysgenesis, including Sertoli-cell-only tubules, immature undifferentiated Sertoli cells, microliths and Leydig cell nodules. The most severe gonadal symptoms occur in patients with disorders of sexual development (DSDs) who have genetic mutations, in whom even sex reversal of individuals with a 46,XY DSD can occur. However, patients with severe DSDs might represent only a small proportion of DSD cases, with milder forms of testicular dysgenesis potentially induced by exposure to environmental and lifestyle factors. Interestingly, maternal smoking during pregnancy has a stronger effect on spermatogenesis than a man's own smoking. Other lifestyle factors such as alcohol consumption and obesity might also have a role. However, increasing indirect evidence exists that exposure to ubiquitous endocrine disrupting chemicals, present at measurable concentrations in individuals, might affect development of human fetal testis. If confirmed, health policies to prevent male reproductive problems should not only target adult men, but also pregnant women and their children.

Persistent environmental pollutants and couple fecundity: an overview

Speculation has arisen that human fecundity may be declining, possibly a function of exposure to persistent environmental chemicals that resist degradation resulting in various pathways for human exposure. In contrast to considerable animal evidence suggesting adverse effects of such chemicals on reproduction, limited human research has been undertaken. To date, available data stem largely from ten unique study cohorts that have quantified individual chemical exposures in relation to time-to-pregnancy (TTP), which is a measure of couple fecundity. Diminished fecundability odds ratios indicative of longer TTP were observed in all but two studies, although not all findings achieved statistical significance. Persistent chemicals associated with reduced couple fecundity as measured by a longer TTP included βHCH, cadmium, lead, mercury, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, TCCD dioxin, and select polybrominated diethers, polychlorinated biphenyls, and perfluorochemicals. Important methodologic limitations need to be considered in weighing the evidence: i) reliance on pregnant women, which may exclude women with the highest exposures if related to the inability to conceive; ii) retrospectively reported TTP, which may be associated with bidirectional reporting errors; and iii) limited attention to male partners or couples' exposures. While current evidence is not inconsistent with animal evidence, concerted efforts to address lingering data gaps should include novel strategies for recruiting couples, the longitudinal measurement of TTP, and the continued enrollment of couples across successive pregnancies. This latter strategy will provide a more complete understanding of the toxicokinetics of chemicals during sensitive windows and their implications for fecundity and its related impairments.