OUP accepted manuscript

Endocrine-disrupting chemicals and female reproductive health: a growing concern

Female fertility and reproductive health depend on a series of developmental steps from embryogenesis through puberty, in addition to the proper functioning of the reproductive system in adulthood. Two important steps are the establishment of the ovarian reserve and development of the hypothalamic-pituitary-ovarian axis. During reproductive years, maintaining an adequate ovarian reserve of follicles as well as balanced neuroendocrine control of reproductive organs is crucial for fertility. Dysregulation of either of these events, during development or in adulthood, can lead to reproductive disorders. Over the past five decades, human fertility rates have declined, whereas the incidence of female reproductive disorders has risen, trends partially linked to environmental factors such as exposure to endocrine-disrupting chemicals (EDCs). Here we outline epidemiological and mechanistic evidence for how EDCs affect the ovarian reserve during early development, its maintenance during adulthood and the establishment of the hypothalamic-pituitary control of puberty and ovulation. Our Review not only reveals strong support for the role of EDC exposure in the development of female reproductive disorders such as abnormal puberty, impaired fertility, premature menopause or polycystic ovarian syndrome, but also highlights knowledge gaps, including the difficulty to prove causality between exposure and human disease manifestation.

Towards an ethics of pronatalism in South Korea (and beyond)

East Asian countries such as South Korea have recently made headlines for experimenting with different methods to incentivise people to have (more) children, in a bid to reverse declining birth rates. Many such incentives-child benefits, cash bonuses, dating events, and so on-appear morally innocuous at first glance. I will demonstrate in this analysis, however, that they amount to stopgap measures which reveal fundamental shortcomings with the way various nation states are approaching the so-called 'problem' of fertility decline.

Cadmium and lead induce mitochondrial dysfunction in ovarian theca Cells: Mechanisms of oxidative stress and bioenergetic collapse

Heavy metals (HMs), particularly lead (Pb) and cadmium (Cd), are hazardous environmental toxicants with toxic effects on female reproductive health. This study investigated the impact of Pb and Cd on mitochondrial energetics in theca interstitial cells (TICs). At their respective EC50 values (15 μM Pb, 5 μM Cd), both metals induced severe mitochondrial impairment, characterized by diminished ATP production and oxygen consumption rates (OCR) alongside loss of mitochondrial membrane potential (MMP). Additionally, Pb and Cd reduced mitochondrial mass, disrupted mitophagy protein expression, and inhibited activities of respiratory chain complexes, paralleled by downregulation of their subunit-coding genes. Both metals elevated lactate production, indicating a metabolic shift toward glycolysis. Structural alterations included increased mitochondrial swelling, enhanced membrane permeability to H+ and K+ ions, and elevated mitochondrial membrane fluidity (MMF) driven by a higher saturated-to-unsaturated fatty acid ratio. These effects were concentration- and time-dependent. Furthermore, Pb and Cd significantly suppressed progesterone and androstenedione secretion, underscoring endocrine disruption. Collectively, our findings demonstrate that Pb and Cd induce mitochondrial dysfunction in TICs through bioenergetic failure, structural damage, and oxidative stress, providing a mechanistic basis for HM-associated reproductive pathologies. Targeting mitochondrial integrity may offer therapeutic potential for mitigating HM-induced ovarian dysfunction in at-risk populations.

Associations between urinary and follicular fluid concentrations of phthalate metabolites and reproductive outcomes in Brazilian women undergoing fertility treatment

Existing literature indicates that phthalates can be toxic to the ovaries, negatively affecting female reproduction and potentially influencing outcomes in assisted reproductive technology (ART). However, data on associations between urinary and/or follicular fluid phthalate concentrations and ART outcomes in South American women are scarce. Therefore, in this prospective study, we recruited 93 women (n = 119 cycles) undergoing ART at a fertility clinic in Brazil. They provided urine and follicular fluid (FF) samples, from which we measured the concentrations of the 15 phthalate metabolites more frequently found in Brazilian populations. We documented both laboratorial and clinical outcomes, estimating associations using negative binomial regression. Our findings revealed that specific oocyte and embryo development parameters were associated with urinary concentrations of phthalate metabolite. Particularly, number of follicles, maturation, as well as blastulation were negatively associated with Mono-benzyl phthalate (MBzP). Similarly, urinary mono-ethyl phthalate (MEP) was associated with lower rates of maturation, good quality and blastulation. However, some parameters positively associated with mono-(carboxyisooctyl) phthalate (MCiOP), including maturation, good quality, and blastulation. We also observed certain associations between embryo development and FF concentrations of phthalate metabolite, although the magnitude and direction of these associations differed among various metabolites. Overall, our results suggest that urinary and FF concentrations of phthalate metabolite may be linked to altered outcomes in ART cycles. However, further studies are needed to clarify the extent of this impact. Our results support previous literature and is the first to evaluate urinary and FF phthalate metabolites concentrations in South American women undergoing infertility treatment.

The special phenotypic characteristics of Dummerstorf superfertile mouse lines could depend on the expression levels of IGF-axis genes

To date, animal models with reproductive phenotypes are knockout or transgenic and typically exhibit reduced fertility or infertility. This limits research to studying single-gene effects or loss of fertility. By contrast, Dummerstorf high-fertility mouse lines 1 and 2 (FL1 and FL2) are two unique outbred selection models that demonstrate exceptional reproductive performance. After approximately 50 years of selection, both lines have doubled the number of ovulated oocytes per cycle and consequently their litter size (>20 vs ∼11) compared to the unselected mice of the same founder population (Dummerstorf FZTDU, ctrl line). FL1 and FL2 exhibit atypical estrous cycle length and altered levels of hormones, such as insulin and leptin, which are associated with GnRH release and/or increased body fat content. Unlike typical cases where these factors impair fertility, they instead contribute to the FLs' high reproductive capacity: the increased ovulation rate results from an upgrade in the quality of their oocytes, influenced by different ovarian lipid profile. In the present study, we analyzed the expression of IGF-axis marker genes linked to reproductive performance and FL-specific traits in three tissues. We found that lepr, which plays a critical role in implantation, was upregulated in the FL1 uterus (1.5-fold vs. ctrl, p < 0.05). In FL1 follicles, igf1, IGF-biding proteins (IGFBP2, IGFBP4) and hsf1-which is involved in gametogenesis-were significantly upregulated (1-4-fold vs. ctrl, p < 0.05 for igf1, hsf1 and IGFBP4; p < 0.01 for igfbp2). In FL2, uterine size was reduced relatively to the body weight (∼0.2 % FL2 vs. 0.25 % in ctrl and 0.28 % in FL1, p < 0.001), indicating that uterus dimensions do not drive their increased litter size. These findings provide new insights into the molecular basis of high fertility and could serve as a foundation for further studies on genotype-phenotype relationships in reproductive biology.

The CFTR K464N variant in fetuses potential increases premature birth risk in Chinese families

BACKGROUND

Global fertility decline has led to increased use of assisted reproductive technology (ART), raising concerns about genetic risks to offspring. This study aimed to investigate cystic fibrosis transmembrane conductance regulator (CFTR) variants in Chinese families and assess their association with pregnancy complications and neonatal outcomes.

METHODS

This prospective cohort study included 446 Chinese families (148 natural conceptions, 298 ART conceptions) who underwent whole genome sequencing. We analyzed the frequency of pathogenic/likely pathogenic CFTR variants and their association with preterm birth (PTB), pregnancy complications, and neonatal outcomes.

RESULTS

Twelve pathogenic/likely pathogenic CFTR variants were identified, with K464N (c.1392G > T) being the most prevalent (2.9% of cohort). PTB incidence was significantly higher in pregnancies with fetal CFTR variants (43.1%, 22/51) compared to those without (17.5%, 69/395; p < 0.001). Fetuses carrying the CFTR K464N variant exhibited a 3.39-fold increased risk of PTB (95% confidence interval (CI): 1.39-8.23, p = 0.007) after adjusting for confounders. Neither fetal nor maternal CFTR variants were significantly associated with other neonatal outcomes, including neonatal weight, Apgar scores, respiratory distress, or hyperbilirubinemia (p > 0.050).

CONCLUSION

These findings suggest a potential association between fetal CFTR K464N variant and increased risk of preterm birth in Chinese families, highlighting the importance of considering CFTR genotyping in prenatal care.

The Potential Protective Role of Mitochondrial Haplogroup R in Ovarian Response: An Exploratory Study

An investigation of the mtDNA haplogroup in 96 Taiwanese women with diminished ovarian response (DOR) and normal ovarian response (NOR) showed that only the haplogroup R is less likely to experience DOR than other mtDNA haplogroups. When analyzing the relationship between age and mitochondria-related markers (mtDNA copy number, ROS levels, and telomere length), it was observed that ROS levels and telomere length exhibited age-dependent changes, and the number of retrieved oocytes decreased with age. However, in the R haplogroup, these mitochondria-related markers remained stable and did not show significant changes with age. Additionally, in the R haplogroup, the number of oocytes did not decline with age, suggesting a unique protective effect associated with this haplogroup. Our study supports the notion that the mtDNA haplogroup may serve as a biomarker for infertility in Taiwanese women.

The dual nature of micronutrients on fertility: too much of a good thing?

OBJECTIVE

To study the effects of generally considered safe doses of antioxidant micronutrient supplementation on semen parameters, systemic redox balance, sperm DNA structural integrity, and fertility.

DESIGN

Given ethical limitations in human studies, this dose escalation study examined the effects of common water-soluble antioxidant micronutrients (vitamin C, zinc, folate, and carnitine) on semen parameters, redox status, DNA integrity, and fertility outcomes in healthy male mice over one spermatogenic cycle. The study was partially repeated at the highest carnitine dose for pregnancy outcomes and comparatively assessed in subfertile, oxidatively stressed mice.

SUBJECTS

"Fertile/healthy" (CD1) and "Subfertile/oxidatively stressed" (gpx5-/-) mice.

EXPOSURE

Water-soluble micronutrients (vitamin C, zinc, folate, and carnitine).

INTERVENTION

N/A MAIN OUTCOME MEASURES: Sperm parameters included count, motility, viability, and acrosome integrity. Systemic redox status was evaluated in blood, measuring malondialdehyde, thiol levels, and total antioxidant capacity. Sperm DNA parameters were examined for oxidation (8-OHdG staining), fragmentation (TUNEL), and decondensation (toluidine blue). Pregnancy outcomes were also assessed in CD1 mice fed carnitine.

RESULTS

In healthy mice, increasing doses of individual micronutrients had minimal effects on semen parameters. However, high doses of all four micronutrients significantly disrupted the redox balance in blood plasma and compromised sperm DNA integrity in an ingredient-specific manner. Moderate to high doses of carnitine caused severe DNA fragmentation, a finding confirmed in a subsequent experiment using the highest carnitine dose. In this follow-up experiment, male mice supplemented with carnitine and mated with females showed decreased pregnancy rates and fewer total pups born. Conversely, in oxidatively stressed mice, high-dose carnitine had the opposite, beneficial effect of improving sperm DNA integrity.

CONCLUSIONS

At high doses, antioxidants can induce reductive stress, damaging vital molecular components of sperm cells such as DNA. Although strong evidence supports the use of preconception antioxidants to boost semen quality, healthcare professionals should assess oxidative stress levels when possible and recommend personalized antioxidant doses to avoid reductive stress and prevent adverse reproductive outcomes.

Decoding the Puzzle of Male Infertility: The Role of Infection, Inflammation, and Autoimmunity

Background/Objectives: Male infertility is a complex, multifactorial condition influenced by infectious, inflammatory, and autoimmune components. Immunological factors, though implicated in reproduction, remain poorly understood. This study aims to deepen the understanding of infections, inflammation, and autoimmune factors in male infertility, with a focus on immune-related disorders affecting the testes and epididymis-immunologically privileged but vulnerable sites. These factors can impair sperm quality through oxidative stress (ROS) and antisperm antibodies (ASA), further compromising fertility. Methods: A narrative review was conducted by analyzing scientific literature from the past 10 years conducted on PubMed using keywords such as "male infertility", "autoimmunity", and "inflammatory disease". Studies focusing on testicular and epididymal disorders, immunological impacts, and therapeutic approaches were included. Results: Our research highlights that conditions like epididymitis, vasectomy, testicular trauma, and previous surgeries can trigger inflammatory responses, leading to ASA formation and oxidative stress. ASA, particularly sperm-immobilizing antibodies, inhibits sperm motility and migration in the female reproductive tract. Infections caused by sexually transmitted bacteria or urinary pathogens frequently induce epididymo-orchitis, a primary contributor to male infertility. While standardized methodologies for ASA testing remain elusive, assisted reproductive treatments such as intracytoplasmic sperm injection (ICSI), in vitro fertilization (IVF), and intrauterine insemination (IUI) show promise in overcoming immune-mediated infertility. Conclusions: This review underscores the critical role of infection, inflammation, and autoimmune responses in male infertility. It highlights the necessity of improving diagnostic methods, understanding immune-pathological mechanisms, and addressing medicolegal issues associated with male infertility. This knowledge could pave the way for innovative therapies, ultimately enhancing fertility outcomes, and mitigating the societal and legal repercussions of infertility.

Net Reproduction Number as a Real-Time Metric of Population Reproducibility

Unlabelled

The total fertility rate (TFR) is a biased estimate of the population reproductive potential when there is a sex-ratio imbalance at birth, and it does not account for the mortality of women of childbearing age. This study aimed to estimate the reproduction rate (Rt), which adjusts for the sex-ratio imbalance and the mortality of women of childbearing age, and to assess the differences in the timing of when the population reached the replacement level of the TFR and Rt. We first estimated the Rt using the probability of survival in women and the number of female births. Then, using a time-series analysis, we compared the time series of the TFR and Rt in the Korean population between 1975 and 2022. We found the Rt showed a below replacement level of the population a year earlier than the TFR. However, the estimate of the time-series analysis of Rt was not significantly different from the estimates of the TFR. Our finding suggests that the Rt can provide timely information on the adjusted population reproductive potential and is easier for the public to interpret compared to TFR.

First evidence of microplastics in human ovarian follicular fluid: An emerging threat to female fertility

Several studies have assessed the presence of microplastics (MPs) in human biological fluids and tissues highlighting potential health risks associated to oxidative stress, inflammation, immune dysfunction, neurotoxicity and reprotoxicity. However, only few studies have evaluated MP presence and effects in ovarian tissues of mammalians and, to date, no studies have detected MPs in human ovarian follicular fluids. Based on these premises, in this study, 18 women (undergoing assisted reproductive treatment at In Vitro Fertilisation center in Salerno, Southern Italy) were selected to assess the presence of MPs in follicular fluid. Plastic particles < 10 µm were measured using Scanning Electron Microscopy (SEM) coupled with an EDX (X Energy Dispersion) detector. MPs (size <10 µm) were detected in 14 out of 18 samples of follicular fluid, with an average concentration of 2191 particles/mL (0-7181particles/mL) and with a mean diameter of 4.48 µm (3.18-5.54 µm). Moreover, a significant correlation between MP concentration in follicular fluid samples and Follicle-Stimulating Hormone (FSH) (p-value <0.05), as well as a weak (non-significant) correlation with Body Mass Index (BMI), age and 17β-estradiol (E2), was found. On the contrary, no correlation with anti-Müllerian Hormone (AMH), fertilization outcomes, miscarriages, or live birth was observed. Since several studies on animal models have demonstrated the negative effects of MPs on ovarian function, the present study, that verified for the first time the presence of MPs in human follicular fluid, is of great significance for the scientific community in terms of raising awareness of the impact that these increasingly pervasive emerging contaminants have on reproductive function and human health.

Extracellular Vesicles in the Aging Male Reproductive System: Progresses and Perspectives

Extracellular vesicles (EVs) serve as crucial mediators of intercellular communication in spermatogenesis, steroidogenesis, and age-related pathophysiological processes within the male reproductive system. These EVs exhibit promising prospects for disease diagnosis and therapeutic administration. This review explores the impact of advanced paternal age on male fertility and testosterone decline, shedding light on the underlying mechanisms. It highlights the decline in semen quality, DNA damage, and alterations in sperm miRNA profiles associated with aging. The interplay between oxidative stress and antioxidants crucially regulates male reproductive aging. Currently, most studies focus on Sertoli cell-derived EVs, while understanding of Leydig cell-derived vesicles remains limited. Multi-omics integration will enhance the understanding of male reproductive aging and guide personalized interventions, revealing potential biomarkers and targets in the future.

Exploring the interplay between inflammation and male fertility

Male fertility results from a complex interplay of physiological, environmental, and genetic factors. It is conditioned by the properly developed anatomy of the reproductive system, hormonal regulation balance, and the interplay between different cell populations that sustain an appropriate and functional environment in the testes. Unfortunately, the mechanisms sustaining male fertility are not flawless and their perturbation can lead to infertility. Inflammation is one of the factors that contribute to male infertility. In the testes, it can be brought on by varicocele, obesity, gonadal infections, leukocytospermia, physical obstructions or traumas, and consumption of toxic substances. As a result of prolonged or untreated inflammation, the testicular resident cells that sustain spermatogenesis can suffer DNA damage, lipid and protein oxidation, and mitochondrial dysfunction consequently leading to loss of function in affected Sertoli cells (SCs) and Leydig cells (LCs), and the formation of morphologically abnormal dysfunctional sperm cells that lay in the basis of male infertility and subfertility. This is due mainly to the production and secretion of pro-inflammatory mediators, including cytokines, chemokines, and reactive oxygen species (ROS) by local immune cells (macrophages, lymphocytes T, mast cells) and tissue-specific cells [SCs, LCs, peritubular myoid cells (PMCs) and germ cells (GCs)]. Depending on the location, duration, and intensity of inflammation, these mediators can exert their toxic effect on different elements of the testes. In this review, we discuss the most prevalent inflammatory factors that negatively affect male fertility and describe the different ways inflammation can impair male reproductive function.

The Fertility Education Initiative: responding to the need for enhanced fertility and reproductive health awareness amongst young people in the United Kingdom

The need for fertility education arises from changing patterns of family formation in recent times. Young people feel unprepared for how best to plan their career and family and have little idea of the various factors that may influence their fertility later in their life. Research shows young people would like to know more and need the information to be conveyed in a way that is engaging and helps them to integrate it at their current life stage. The Fertility Education Initiative (FEI) was founded in 2016 to address the need for improved fertility and reproductive health awareness and ensure young people are equipped with the relevant information to meet their reproductive and family building needs. This paper serves as a historical record of the genesis of the FEI and its impact to date.

Paternal age, de novo mutations, and offspring health? New directions for an ageing problem

This Directions article examines the mechanisms by which a father's age impacts the health and wellbeing of his children. Such impacts are significant and include adverse birth outcomes, dominant genetic conditions, neuropsychiatric disorders, and a variety of congenital developmental defects. As well as age, a wide variety of environmental and lifestyle factors are also known to impact offspring health via changes mediated by the male germ line. This picture of a dynamic germ line responsive to a wide range of intrinsic and extrinsic factors contrasts with the results of trio studies indicating that the incidence of mutations in the male germ line is low and exhibits a linear, monotonic increase with paternal age (∼two new mutations per year). While the traditional explanation for this pattern of mutation has been the metronomic plod of replication errors, an alternative model pivots around the 'faulty male' hypothesis. According to this concept, the genetic integrity of the male germ line can be dynamically impacted by age and a variety of other factors, and it is the aberrant repair of such damage that drives mutagenesis. Fortunately, DNA proofreading during spermatogenesis is extremely effective and these mutant cells are either repaired or deleted by apoptosis/ferroptosis. There appear to be only two mechanisms by which mutant germ cells can escape this apoptotic fate: (i) if the germ cells acquire a mutation that by enhancing proliferation or suppressing apoptosis, permits their clonal expansion (selfish selection hypothesis) or (ii) if a genetically damaged spermatozoon manages to fertilize an oocyte, which then fixes the damage as a mutation (or epimutation) as a result of defective DNA repair (oocyte collusion hypothesis). Exploration of these proposed mechanisms should not only help us better understand the aetiology of paternal age effects but also inform potential avenues of remediation.

Exposure to residential green space and semen quality among Chinese men

BACKGROUND

Residential greenness has been linked to various health benefits, but evidence on its association with sperm quality remains limited.

METHODS

We enrolled 28,089 adult men from an infertility clinic in Hubei, China, from 2014 to 2020. Residential greenness was estimated using the Normalized Vegetation Index (NDVI) from satellite imagery, averaged within buffers of 250 m, 500 m and 1000 m around each participant's residential address. We employed multivariate linear regression analysis to evaluate the association between NDVI exposure and semen quality, while controlling for individual characteristics and semen collection season. Additionally, we performed subgroup analyses to investigate potential variations in the association based on individual characteristics.

RESULTS

An interquartile range increase of 0.243 in NDVI within the 1000 m buffer was associated with increases of 1.68 % (95 % CI: 0.31 %, 3.06 %) in sperm concentration, 0.43 % (95 % CI: 0.08 %, 0.79 %) in progressive motility, and 0.50 % (95 % CI: 0.14 %, 0.87 %) in total motility. These associations were consistent across different buffer sizes. The associations were more pronounced during the 70-90 lag days prior to semen collection (spermatogenesis stage) and among men aged ≥ 40 years or those with lower education levels.

CONCLUSIONS

Our study demonstrated that exposure to residential greenness may act as an innovative protective factor for semen quality.

An Evaluation of Controversial Statements in Etica Teologica Della Vita

The teachings of the Catholic Church on human sexuality, contraception and the treatment of infertility are well established and clearly explained in many Church documents, including Humanae vitae and Familiaris consortio. In 2022, a book was published in Italian which reported on a seminar organised by an Academy of the Catholic Church about the ethics of life. Titled the Theological Ethics of Life (abbreviated 'ETV' in Italian), the conclusion of chapter VII contains statements about contraception and assisted reproductive technologies (ART) which, though somewhat difficult to interpret, appear to be controversial with regard to accepted Church teaching on these subjects. This paper presents a detailed analysis by a group of Australian Catholic doctors and ethicists of an English translation of paragraphs 172 and 173 of ETV and concludes that they contain statements which deviate from and contradict accepted Catholic teaching on contraception and ART. The authors also claim that a thorough up-to-date knowledge and understanding of suitable current alternatives to contraception and ART (e.g. in-vitro fertilization, IVF) which are safe, effective, readily accessible and consistent with Catholic ethics appears to be lacking in paragraphs 172 and 173 of ETV. The authors suggest a better understanding of currently available methods to assist with fertility care, aided by input from Catholic medical experts working in the areas of Fertility Awareness Methods (FAMs) and Restorative Reproductive Medicine (RRM) would better inform ongoing debates about contraception and ART within the Church and be of service to the Faithful who should be encouraged to pursue these alternatives which are both effective and consistent with Church teaching on human sexuality and morals.

Exploring the determinants of fertility rates in Ethiopia: a decomposition analysis using count regression models with a focus on urban and rural residence, based on the 2019 Ethiopian demographic health survey

INTRODUCTION

Fertility refers to the biological capacity to reproduce and have children. It is a key aspect of reproductive health influenced by various factors. Therefore, this study aims to explore the determinants of fertility rates based on urban and rural settings in Ethiopia.

METHOD

A stratified two-stage cluster sampling approach was used, employing data from the 2019 Ethiopian Mini Demographic and Health Survey ( https://dhsprogram.com ). The study comprised 8,885 women aged 15 to 49 years. The study employed Stata 17, and the data was described using descriptive statistics. Associations were examined using decomposition analysis and negative binomial regression. The Incidence Rate Ratio and p-value were used to determine the statistical significance of the variables examined.

RESULTS

The negative binomial regression found that factors such as maternal age (IRR, 1.08, P-value,0.00), living in rural (IRR,1.09, P-value,0.00), being Muslim (IRR,1.13, P-value,0.00), being from other religious groups (IRR,1.16, P-value,0.00), having six up to nine household members (IRR,1.24, P-value,0.00), having greater than nine household member(IRR,1.14, P-value,0.04), having one child under five year (IRR,1.35, P-value,0.00), having two children under five year (IRR,1.77, P-value,0.00), and having more than two under five years (IRR,1.99, P-value,0.00), being currently pregnant (IRR,1.08, P-value,0.00), use of contraceptive(IRR,1.13, P-value,0.00) are positively associated with bearing more children. On the other hand, completing primary education (IRR,0.84, P-value,0.00), secondary education (IRR,0.61, P-value,0.00), being from the richest household (IRR = 0.94, P-value,0.00), and being single/divorced and widowed (IRR,0.49, P-value,0.00) are negatively associated with having more children because their IRR is less than one. The decomposition analysis also demonstrated that marital status has a stronger negative correlation with fertility in rural compared to urban settings. Additionally, the number of children under five exerts a greater influence on fertility in urban areas.

CONCLUSION

the study found significant rural-urban differences in the factors shaping fertility in Ethiopia. While demographics like maternal age, education, and wealth influenced fertility in both settings, the relationships varied in nature and magnitude. To address this, Policymakers should develop targeted fertility programs that address the unique needs and challenges faced by rural and urban populations.

Decline in and recovery of fertility rates after COVID-19-related state of emergency in Japan

INTRODUCTION

The COVID-19 pandemic led to a decline in fertility rates worldwide. Although many regions have experienced a temporary drop in fertility rates with the spread of the infection, subsequent recovery has varied across countries. This study aimed to evaluate the impact of COVID-19 infection rates and regional sociodemographic factors on the recovery of fertility rates in Japan following the state of emergency.

METHODS

This study examined prefectural fertility data from before the COVID-19 pandemic to forecast fertility rates up to 2022 using a seasonal autoregressive integrated moving average model. A regression analysis was conducted on fertility rates during the first state of emergency and the subsequent recovery rate with respect to the number of new COVID-19 cases and sociodemographic factors specific to each prefecture.

RESULTS

During the first state of emergency, the monthly fertility rate decreased by an average of -13.8% (SD: 6.26, min: -28.78, max: 0.15) compared with the previous year. Over the following 22 months, the average fertility recovery rate was +2.31% (SD: 3.57; min: -8.55, max: 19.54). Multivariate analysis of the impact of the pandemic on fertility changes during the first emergency indicated a negative correlation between new COVID-19 cases per capita and the proportion of nuclear households. No significant correlation was found between fertility recovery rate and new COVID-19 cases or emergency duration. When classifying fertility rate fluctuation patterns before and after the emergency into four clusters, variations were noted in the proportion of the elderly population, marriage divorce rate and the number of internet searches related to pregnancy intentions across the clusters.

CONCLUSIONS

No association was found between pregnancy intentions related to the spread of infection, such as the number of new cases and the fertility recovery rate following the first state of emergency. Differences in the patterns of decline and recovery during the pandemic were observed based on population composition and internet searches for infection and pregnancy across different prefectures.

Anti-Müllerian hormone as a diagnostic marker for testicular degeneration in dogs: insights from cryptorchid models

Introduction

The increasing prevalence of infertility in male dogs in clinical practice mirrors current trends seen in human medicine. Acquired infertility is notably more common in dogs compared to congenital causes, with conditions such as testicular degeneration leading to irreversible loss of fertility. Current diagnostic methods for testicular degeneration, such as histopathological and cytological examinations, rely on testicular biopsy or fine needle aspiration, making them less feasible for routine use. Anti-Müllerian hormone (AMH), produced by Sertoli cells, has emerged as a potential alternative biomarker for testicular health, which can be measured in serum. This study evaluates AMH as a potential marker for testicular degeneration, using cryptorchid dogs as models for impaired fertility and altered testicular histology.

Methods

The relationship between serum AMH levels and AMH tissue expression with impaired spermatogenesis and altered histology was investigated. Serum AMH levels were determined in intact, cryptorchid, and castrated individuals using an immuno-enzymatic ELISA kit and compared between subgroups based on testicular location. Tissue AMH immuno-expression was differentially quantified in two regions of interest (ROIs), the interstitial space and the seminiferous tubule, in both descended and retained gonads. Furthermore, testicles were analyzed using histomorphometric analysis in seminiferous tubules, while spermatogenesis was evaluated using the Johnsen score.

Results

Serum AMH levels were positively correlated with AMH expression assessed in both interstitial space (ρ = 0.494, p ≤ 0.01) and seminiferous tubules (ρ = 0.610, p ≤ 0.001). Conversely, serum AMH levels showed a negative correlation with the seminiferous tubule area (ρ = -0.435, p ≤ 0.05). Smaller seminiferous tubule areas were linked to increased AMH reactivity in both seminiferous tubules (ρ = -0.774, p ≤ 0.001) and interstitial space (ρ = -0.725, p ≤ 0.001). Additionally, lower Johnsen scores were associated with higher serum AMH levels (ρ = -0.537, p ≤ 0.01) and elevated AMH expression in both seminiferous tubules (ρ = -0.756, p ≤ 0.001) and interstitial space (ρ = -0.679, p ≤ 0.001).

Discussion

Our results suggest that higher serum levels and tissue expression of AMH are linked to smaller seminiferous tubules and poorer Johnsen scores, reflecting degenerative changes and Sertoli cell dysfunction in retained testicles. Given the similarities in the mechanisms that increase AMH levels in both cryptorchid and non-cryptorchid testicles affected by testicular degeneration, this study recommends using AMH as a marker for diagnosing testicular degeneration in dogs.

The methodological and ethical concerns of genetic studies of same-sex sexual behavior

Same-sex sexual behavior has long interested genetics researchers in part because, while there is evidence of heritability, the trait as typically defined is associated with fewer offspring. Investigations of this phenomenon began in the 1990s with linkage studies and continue today with the advent of genome-wide association studies. As this body of research grows, so does critical scientific and ethical review of it. Here, we provide a targeted overview of existing genetics studies on same-sex sexual behavior, highlight the ethical and scientific considerations of this nascent field, and provide recommendations developed by the authors to enhance social and ethical responsibility.

From spermatogonia to spermatozoa: Filling gaps in andrology at the 16th Network of Young Researchers in Andrology meeting

The 16th Network of Young Researchers in Andrology meeting, hosted at the Sleepwell Hostel in Brussels, Belgium, was the first Network of Young Researchers in Andrology meeting as the young arm of the European Academy of Andrology. Over three days, this vibrant event provided a valuable platform for early-career researchers in andrology to present and discuss their research. With 41 attendees from 12 different countries, the meeting featured a diverse scientific program including keynote lectures from six world-leading experts, covering a broad range of topics in andrology. The 16th Network of Young Researchers in Andrology meeting showcased advancements in fertility preservation, single-cell applications, in vitro testis modeling, and epigenetics. Networking opportunities were a key highlight, featuring a scientific speed-dating session and a networking dinner designed to foster meaningful connections and collaborations among participants. The meeting concluded with a workshop on the science of sleep, offering attendees practical strategies to enhance their rest and well-being. Overall, the 16th Network of Young Researchers in Andrology meeting significantly advanced the audience's knowledge, strengthened the network of young researchers, and underlined Network of Young Researchers in Andrology's commitment to supporting and collaborating with emerging scientists in the andrology community.

Antioxidants and Fertility in Women with Ovarian Aging: A Systematic Review and Meta-Analysis

Ovarian aging is a major factor for female subfertility. Multiple antioxidants have been applied in different clinical scenarios, but their effects on fertility in women with ovarian aging are still unclear. To address this, a meta-analysis was performed to evaluate the effectiveness and safety of antioxidants on fertility in women with ovarian aging. A total of 20 randomized clinical trials with 2617 participants were included. The results showed that use of antioxidants not only significantly increased the number of retrieved oocytes and high-quality embryo rates but also reduced the dose of gonadotropin, contributing to higher clinical pregnancy rates. According to the subgroup analysis of different dose settings, better effects were more pronounced with lower doses; in terms of antioxidant types, coenzyme Q10 (CoQ10) tended to be more effective than melatonin, myo-inositol, and vitamins. When compared with placebo or no treatment, CoQ10 showed more advantages, whereas small improvements were observed with other drugs. In addition, based on subgroup analysis of CoQ10, the optimal treatment regimen of CoQ10 for improving pregnancy rate was 30 mg/d for 3 mo before the controlled ovarian stimulation cycle, and women with diminished ovarian reserve clearly benefited from CoQ10 treatment, especially those aged <35 y. Our study suggests that antioxidant consumption is an effective and safe complementary therapy for women with ovarian aging. Appropriate antioxidant treatment should be offered at a low dose according to the patient's age and ovarian reserve. This study was registered at PROSPERO as CRD42022359529.

Population decline: where demography, social science, and biology intersect

In brief

Over the past half century, the world has witnessed an unprecedented decline in human fertility rates. This analysis reviews the various socioeconomic, cultural, and biological factors involved in driving this change and considers whether low fertility rates are a temporary or permanent feature of our future demographic profile.

Abstract

Since the early 1960s, the world has witnessed the spectacular collapse of human fertility. As a result of this phenomenon, several countries are already seeing their population numbers fall and more will follow in the coming decades. The causes of this fertility decline involve a complex interplay of socio-economic, environmental, and biological factors that have converged to constrain fertility in posterity's wake. Since large numbers of offspring are no longer needed to compensate for high infant mortality in contemporary society, couples have opted to have small families in a quality-over-quantity investment in their progeny's future. Simultaneously, increases in female education, the enhanced participation of women in the paid workforce, and a resultant delay in childbearing has placed limits on achievable family size. Progressive urbanization, the improved availability of contraceptives, and the socio-economic pressures experienced by young adults in ageing societies are also contributing to fertility's demise. These factors, together with the individualism that pervades modern society and the increasing social acceptability of voluntary childlessness, have firmly established a low fertility ethos in most post-transition countries. Since none of these forces are about to relent, it looks as if extremely low fertility might be with us for some time to come. This may have long-term consequences. The lack of selection pressure on high fertility genotypes, the ability of ART to retain poor fertility genotypes within the population, and sustained exposure to reproductive toxicants in modern industrialized environments may all contrive to leave a permanent mark on the fecundity of our species.

The current 'dramatically' high paternal ages at childbirth are not unprecedented

There is strong individual-level evidence that late fatherhood is related to a wide range of health disorders and conditions in offspring. Over the last decades, mean paternal ages at childbirth have risen drastically. This has alarmed researchers from a wide range of fields. However, existing studies have an important shortcoming in that they lack a long-term perspective. This article is a step change in providing such a long-term perspective. We unveil that in many countries the current mean paternal ages at childbirth and proportions of fathers of advanced age at childbirth are not unprecedented. Taking the detected U-shaped trend pattern into account, we discuss individual- and population-level implications of the recent increases in paternal ages at childbirth and highlight important knowledge gaps. At the individual level, some of the biological mechanisms that are responsible for the paternal age-related health risk might, at least to some degree, be counterbalanced by various social factors. Further, how these individual-level effects are linked to population health and human cognitive development might be influenced by various factors, including technical advances and regulations in prenatal diagnostics.

Evaluation of telomere length and telomerase activity on predicting in vitro fertilization treatment outcomes

The current article is a literature review aiming to provide an overview of the existing knowledge on the association between telomere length and telomerase activity and in vitro fertilization. Recently, telomeres have been used as an effective biomarker to determine biological age, which may differ from chronological age due to genetic, lifestyle, and environmental factors. Cellular senescence, along with other exogenous and mainly environmental factors, can enhance telomere wear, further shortening their ends and may also affect reproductive aging. IVF is a common fertility treatment caused by female reasons (age, ovulation disorders, damaged or blocked fallopian tubes, endometriosis), male reasons (low sperm quantity or quality), or unexplained infertility. A growing number of studies have proposed a relationship between telomere length and telomerase activity and IVF success and have suggested their use as candidate biomarkers for IVF outcome. Nevertheless, additional studies are necessary to be conducted, in order to clarify the possible implication of telomeres in IVF and to evaluate their possible role as valuable predictors of IVF result.

What is driving the global decline of human fertility? Need for a multidisciplinary approach to the underlying mechanisms

An intense period of human population expansion over the past 250 years is about to cease. Total fertility rates are falling dramatically all over the world such that highly industrialized nations, including China and the tiger economies of SE Asia, will see their populations decline significantly in the coming decades. The socioeconomic, geopolitical and environmental ramifications of this change are considerable and invite a multidisciplinary consideration of the underlying mechanisms. In the short-term, socioeconomic factors, particularly urbanization and delayed childbearing are powerful drivers of reduced fertility. In parallel, lifestyle factors such as obesity and the presence of numerous reproductive toxicants in the environment, including air-borne pollutants, nanoplastics and electromagnetic radiation, are seriously compromising reproductive health. In the longer term, it is hypothesized that the reduction in family size that accompanies the demographic transition will decrease selection pressure on high fertility genes leading to a progressive loss of human fecundity. Paradoxically, the uptake of assisted reproductive technologies at scale, may also contribute to such fecundity loss by encouraging the retention of poor fertility genotypes within the population. Since the decline in fertility rate that accompanies the demographic transition appears to be ubiquitous, the public health implications for our species are potentially devastating.

Current global status of male reproductive health

BACKGROUND

The widespread interest in male reproductive health (MRH), fueled by emerging evidence, such as the global decline in sperm counts, has intensified concerns about the status of MRH. Consequently, there is a pressing requirement for a strategic, systematic approach to identifying critical questions, collecting pertinent information, and utilizing these data to develop evidence-based strategies. The methods for addressing these questions and the pathways toward their answers will inevitably vary based on the variations in cultural, geopolitical, and health-related contexts. To address these issues, a conjoint ESHRE and Male Reproductive Health Initiative (MRHI) Campus workshop was convened.

OBJECTIVE AND RATIONALE

The three objectives were: first, to assess the current state of MRH around the world; second, to identify some of the key gaps in knowledge; and, third, to examine how MRH stakeholders can collaboratively generate intelligent and effective paths forward.

SEARCH METHODS

Each expert reviewed and summarized the current literature that was subsequently used to provide a comprehensive overview of challenges related to MRH.

OUTCOMES

This narrative report is an overview of the data, opinions, and arguments presented during the workshop. A number of outcomes are presented and can be summarized by the following overarching themes: MRH is a serious global issue and there is a plethora of gaps in our understanding; there is a need for widespread international collaborative networks to undertake multidisciplinary research into fundamental issues, such as lifestyle/environmental exposure studies, and high-quality clinical trials; and there is an urgent requirement for effective strategies to educate young people and the general public to safeguard and improve MRH across diverse population demographics and resources.

LIMITATIONS REASONS FOR CAUTION

This was a workshop where worldwide leading experts from a wide range of disciplines presented and discussed the evidence regarding challenges related to MRH. While each expert summarized the current literature and placed it in context, the data in a number of areas are limited and/or sparse. Equally, important areas for consideration may have been missed. Moreover, there are clear gaps in our knowledge base, which makes some conclusions necessarily speculative and warranting of further study.

WIDER IMPLICATIONS

Poor MRH is a global issue that suffers from low awareness among the public, patients, and heathcare professionals. Addressing this will require a coordinated multidisciplinary approach. Addressing the significant number of knowledge gaps will require policy makers prioritizing MRH and its funding.

STUDY FUNDING/COMPETING INTERESTS

The authors would like to extend their gratitude to ESHRE for providing financial support for the Budapest Campus Workshop, as well as to Microptic S.L. (Barcelona) for kindly sponsoring the workshop. P.B. is the Director of the not-for-profit organization Global Action on Men's Health and receives fees and expenses for his work, (which includes the preparation of this manuscript). Conflicts of interest: C.J.D.J., C.L.R.B., R.A.A., P.B., M.P.C., M.L.E., N.G., N.J., C.K., AAP, M.K.O., S.R.-H., M.H.V.-L.: ESHRE Campus Workshop 2022 (Travel support-personal). C.J.D.J.: Cambridge University Press (book royalties-personal). ESHRE Annual Meeting 2022 and Yale University Panel Meeting 2023 (Travel support-personal). C.L.R.B.: Ferring and IBSA (Lecture), RBMO editor (Honorarium to support travel, etc.), ExSeed and ExScentia (University of Dundee), Bill & Melinda Gates Foundation (for research on contraception). M.P.C.: Previously received funding from pharmaceutical companies for health economic research. The funding was not in relation to this work and had no bearing on the contents of this work. No funding from other sources has been provided in relation to this work (funding was provided to his company Global Market Access Solutions). M.L.E.: Advisor to Ro, Doveras, Next, Hannah, Sandstone. C.K.: European Academy of Andrology (Past president UNPAID), S.K.: CEO of His Turn, a male fertility Diagnostic and Therapeutic company (No payments or profits to date). R.I.M.: www.healthymale.org.au (Australian Government funded not for profit in men's health sector (Employed as Medical Director 0.2 FET), Monash IVF Pty Ltd (Equity holder)). N.J.: Merck (consulting fees), Gedeon Richter (honoraria). S.R.-H.: ESHRE (Travel reimbursements). C.N.: LLC (Nursing educator); COMMIT (Core Outcomes Measures for Infertility Trials) Advisor, meeting attendee, and co-author; COMMA (Core Outcomes in Menopause) Meeting attendee, and co-author; International Federation of Gynecology and Obstetrics (FIGO) Delegate Letters and Sciences; ReproNovo, Advisory board; American Board of Urology Examiner; American Urological Association Journal subsection editor, committee member, guidelines co-author Ferring Scientific trial NexHand Chief Technology Officer, stock ownership Posterity Health Board member, stock ownership. A.P.: Economic and Social Research Council (A collaborator on research grant number ES/W001381/1). Member of an advisory committee for Merck Serono (November 2022), Member of an advisory board for Exceed Health, Speaker fees for educational events organized by Mealis Group; Chairman of the Cryos External Scientific Advisory Committee: All fees associated with this are paid to his former employer The University of Sheffield. Trustee of the Progress Educational Trust (Unpaid). M.K.O.: National Health and Medical Research Council and Australian Research Council (Funding for research of the topic of male fertility), Bill and Melinda Gates Foundation (Funding aimed at the development of male gamete-based contraception), Medical Research Future Fund (Funding aimed at defining the long-term consequences of male infertility). M.H.V.-L.: Department of Sexual and Reproductive Health and Research (SRH)/Human Reproduction Programme (HRP) Research Project Panel RP2/WHO Review Member; MRHI (Core Group Member), COMMIT (member), EGOI (Member); Human Reproduction (Associate Editor), Fertility and Sterility (Editor), AndroLATAM (Founder and Coordinator).

The effect of gradually lifting the two-child policy on demographic changes in China

Low-fertility rate has been a common problem in many industrialized countries. To reverse the declining trend of new births, Chinese government gradually lifted its restrictions on the number of births per family, allowing for a household to have no more than two children. Little is known about the additional births or population increase contributed by the gradual relaxation of birth restrictions. To fill this gap, this quasi-experimental design study including data from 124 regions used the synthetic control method and controlled interrupted time series analysis to evaluate the differences in birth rates and rates of natural population increase between China and its synthetic control following implementation of the two-child policy from 2011 to 2020. A total of 123 regions were included in the control pool. Data collected during 1990-2010 were used to identify the synthetic China for each study outcome. The mean rate differences of birth rates and rates of natural increase between China and synthetic China after two-child policy implementation were 1.16 per 1000 population and 1.02 per 1000, respectively. These rate differences were distinguished from variation due to chance (one-sided pseudo-P-values: P for birth rates = 0.047, P for rates of natural increase = 0.020). However, there were statistically significant annual reductions in the pre-post trend of birth rates and rates of natural increase compared with those of controls of <0.340 per 1000 population per year [P = 0.007, 95% CI = (-0.584, -0.096)] and <0.274 per 1000 per year [P = 0.028, 95% CI = (-0.518, -0.031)]. The results suggested that lifting birth restrictions had a short-term effect on the increase in birth rates and rates of natural population increase. However, birth policy with lifting birth restrictions alone may not have sustained impact on population growth in the long run.

Early or late menarche is associated with reduced fecundability in the Norwegian Mother, Father and Child Cohort Study

STUDY QUESTION

Is age at menarche associated with fecundability?

SUMMARY ANSWER

Both early (<11 years) and late (>15 years) menarche is associated with decreased fecundability.

WHAT IS KNOWN ALREADY

Previous studies on age at menarche and fecundability have been inconclusive. Women with early or late menarche are at increased risks of gynaecological and autoimmune diseases that may affect their ability to conceive.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective cohort study including 67 613 pregnant women, participating in the Norwegian Mother, Father and Child Cohort Study between 1999 and 2008, with self-reported information on age at menarche and time to pregnancy. We included planned pregnancies that were conceived either naturally or with the help of assisted reproductive technologies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We calculated fecundability ratios (FRs) with 95% CIs representing the cycle-specific probability of conception by categories of age at menarche. FRs were adjusted for participants' pre-pregnancy body mass index, highest completed or ongoing education level, and age at initiation of trying to conceive.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed a 7% lower probability of conceiving during any given menstrual cycle up to 12 cycles in women with early or late menarche. Among women with menarche >15 years, the adjusted FR was 0.93 (95% CI: 0.90-0.97), and among women with menarche <11 years, the adjusted FR was 0.93 (95% CI: 0.89-0.99), when compared to women with menarche between 12 and 14 years.

LIMITATIONS, REASONS FOR CAUTION

The study-population consisted of women pregnant in their second trimester, excluding those with persistent infertility. Recall of age at menarche and time to pregnancy may be inaccurate.

WIDER IMPLICATIONS OF THE FINDINGS

Both early (<11 years) and late (>15 years) menarche was associated with decreased fecundability. Women experiencing early menarche or late menarche may be counselled accordingly.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Norwegian Institute of Public Health, Oslo, Norway, and by Telemark Hospital Trust, Porsgrunn, Norway and was partly supported by the Research Council of Norway through its centres of excellence funding scheme (project number 262700) and the Research Council of Norway (project no. 320656). The project was co-funded by the European Union (ERC, BIOSFER, 101071773). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. M.C.M. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 947684). The authors report no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Associations between multiple metal exposure and fertility in women: A nested case-control study

Metal pollution can cause a decline in female fertility, however, previous studies have focused more on the effect of a single metal on fertility. In this study, we evaluated the effect of metal mixtures on female fertility based on nested case-control samples. The plasma levels of 22 metal elements from 180 women were determined by an inductively coupled plasma mass spectrometer (ICP-MS). Minimum absolute contraction and selection operator (LASSO) penalty regression selected metals with the greatest influence on clinical outcome. Logistic regression was used to analyze the correlation between single metals and fertility while a Bayesian kernel function regression (BKMR) model was used to analyze the effect of mixed metals. Eight metals (Calcium (Ca), Chromium (Cr), Cobalt (Co), Copper (Cu), Zinc (Zn), Rubidium (Rb), Strontium (Sr) and Zirconium (Zr)) were selected by LASSO regression for subsequent analysis. After adjusting for covariates, the logistic model showed that Cu (Odds Ratio(OR):0.33, 95% CI: 0.13 - 0.84) and Co (OR:0.38, 95% CI: 0.15 -0.94) caused a significant reduction in fertility, and identified the protective effect of Zn (OR: 2.96, 95% CI:1.21 -7.50) on fertility. Trend tests showed that increased Cr, Cu, and Rb levels were associated with reduced fertility. The BKMR model showed that Cr, Co, Cu, and Rb had a nonlinear relationship with fertility decline when controlling for the concentrations of other metals and suggested that Cu and Cr might exert an influence on fertility. Analysis showed a negative correlation between Cu, Cr, Co, Rb, and fertility, and a positive correlation between Zn and fertility. Furthermore, we found evidence for the interaction between Cu and Cr. Our findings require further validation and may identify new mechanisms in the future.

Declining global fertility rates and the implications for family planning and family building: an IFFS consensus document based on a narrative review of the literature

BACKGROUND

Family-planning policies have focused on contraceptive approaches to avoid unintended pregnancies, postpone, or terminate pregnancies and mitigate population growth. These policies have contributed to significantly slowing world population growth. Presently, half the countries worldwide exhibit a fertility rate below replacement level. Not including the effects of migration, many countries are predicted to have a population decline of >50% from 2017 to 2100, causing demographic changes with profound societal implications. Policies that optimize chances to have a child when desired increase fertility rates and are gaining interest as a family-building method. Increasingly, countries have implemented child-friendly policies (mainly financial incentives in addition to public funding of fertility treatment in a limited number of countries) to mitigate decreasing national populations. However, the extent of public spending on child benefits varies greatly from country to country. To our knowledge, this International Federation of Fertility Societies (IFFS) consensus document represents the first attempt to describe major disparities in access to fertility care in the context of the global trend of decreasing growth in the world population, based on a narrative review of the existing literature.

OBJECTIVE AND RATIONALE

The concept of family building, the process by which individuals or couples create or expand their families, has been largely ignored in family-planning paradigms. Family building encompasses various methods and options for individuals or couples who wish to have children. It can involve biological means, such as natural conception, as well as ART, surrogacy, adoption, and foster care. Family-building acknowledges the diverse ways in which individuals or couples can create their desired family and reflects the understanding that there is no one-size-fits-all approach to building a family. Developing education programs for young adults to increase family-building awareness and prevent infertility is urgently needed. Recommendations are provided and important knowledge gaps identified to provide professionals, the public, and policymakers with a comprehensive understanding of the role of child-friendly policies.

SEARCH METHODS

A narrative review of the existing literature was performed by invited global leaders who themselves significantly contributed to this research field. Each section of the review was prepared by two to three experts, each of whom searched the published literature (PubMed) for peer reviewed full papers and reviews. Sections were discussed monthly by all authors and quarterly by the review board. The final document was prepared following discussions among all team members during a hybrid invitational meeting where full consensus was reached.

OUTCOMES

Major advances in fertility care have dramatically improved family-building opportunities since the 1990s. Although up to 10% of all children are born as a result of fertility care in some wealthy countries, there is great variation in access to care. The high cost to patients of infertility treatment renders it unaffordable for most. Preliminary studies point to the increasing contribution of fertility care to the global population and the associated economic benefits for society.

WIDER IMPLICATIONS

Fertility care has rarely been discussed in the context of a rapid decrease in world population growth. Soon, most countries will have an average number of children per woman far below the replacement level. While this may have a beneficial impact on the environment, underpopulation is of great concern in many countries. Although governments have implemented child-friendly policies, distinct discrepancies in access to fertility care remain.

KLF2 controls proliferation and apoptosis of human spermatogonial stem cells via targeting GJA1

Human spermatogonial stem cells (SSCs) are essential for spermatogenesis and male fertility. However, molecular mechanisms regulating fate determinations of human SSCs remain elusive. In this study, we revealed that KLF2 decreased the proliferation, DNA synthesis, and colonization of human SSCs as well as increased apoptosis of these cells. We identified and demonstrated that GJA1 was a target gene for KLF2 in human SSCs. Notably, KLF2 overexpression rescued the reduction of proliferation of human SSCs caused by GJA1 silencing as well as the enhancement of apoptosis of human SSCs. Abnormalities in the higher level of KLF2 and/or KIF2 mutations might lead to male infertility. Collectively, these results implicate that KLF2 inhibits proliferation of human SSCs and enhances their apoptosis by targeting GJA1. This study thus provides novel genetic mechanisms underlying human spermatogenesis and azoospermia, and it offers new endogenous targets for treating male infertility.

Decrease in Sperm Parameters in the 21st Century: Obesity, Lifestyle, or Environmental Factors? An Updated Narrative Review

Semen quality represents a compelling factor for fertility, and delineating the normal values has proven difficult. In the last four decades, several authors have reported a noticeable decline in sperm parameters. Also, studies investigating 'time to pregnancy' have shown that fecundity begins to be reduced when sperm numbers decrease below 30 million, even though according to the 6th edition of the WHO manual, the normal value is currently 16 million/mL or 39 million per ejaculate. There exists sufficient data to suggest a decline in sperm counts over time, even though the clear reason for this adverse trend is not well established, but some associations have been hypothesised, such as maternal smoking during pregnancy. Additional potential factors have yet to be fully illustrated but involve poor diet, increased obesity, and exposure to environmental toxins. Moreover, the change in environmental conditions and more common exposure to endocrine-disrupting chemicals (EDCs), such as pesticides and herbicides, as well as bisphenol A, phthalates, polychlorinated biphenyls, and heavy metals, starting from prenatal life and continuing into adulthood, may exhibit probable features explaining the reduction in sperm parameters. Therefore, the main goal of this narrative review is to furnish an overview of the possible effects of exposure to EDCs on testicular function and spermatogenesis and, also, to summarise the evidence regarding a decrease in sperm quality and examine its potential consequences.

Empowering tomorrow's leaders: the impact of the 15th Network of Young Researchers in Andrology (NYRA) meeting on male reproductive health and interdisciplinary collaboration

The 15th Network of Young Researchers in Andrology (NYRA) meeting, held at the Palace de Caux, Switzerland, served as a valuable platform to disseminate cutting-edge research and facilitate interactions among early-career researchers and trainees in andrology from around the world. Preceding the 22nd European Testis Workshop, the 2-day event brought together participants from a variety of countries to discuss a range of topics pertaining to men's reproductive health and biology. Specific focuses included piRNAs in mammalian reproduction, biomolecules enhancing sperm physiology, advances in in vitro spermatogenesis, reproductive strategies across species, and career development. A dedicated 'scientific speed-dating' social event also stood out, encouraging cross-disciplinary collaborations and strengthening ties within the scientific community. The high participation rate of the meeting highlighted its value in connecting the andrology community. Finally, the announcement of NYRA's merger with the European Academy of Andrology (EAA) marked a pivotal moment, enabling NYRA to support young researchers while collaborating with the EAA to advance andrology research. The 15th NYRA meeting played a crucial role in enhancing knowledge dissemination and andrology research, empowering young researchers, and addressing key challenges in male infertility.

DEFB126 2-nt Deletion (rs11467417) as a Potential Risk Factor for Chlamydia Trachomatis Infection and Subsequent Infertility in Iranian Men

Background

Chlamydia trachomatis (CT) is one of the most prevalent sexually transmitted infections, causing genital tract infections and infertility. Defensins have an immunomodulatory function and play an important role in sperm maturation, motility, and fertilization. DEFB126 is present on ejaculated spermatozoa and is essential for them to pass through the female reproductive tract. The purpose of the study was to determine the frequency of the 2-nt deletion of the DEFB126 (rs11467417) in Iranian infertile males with a recurrent history of CT.

Methods

Semen samples of 1080 subfertile males were investigated. Among patients who had CT-positive results, sperm DNA from 50 symptomatic and 50 asymptomatic patients were collected for the DEFB126 genotype analysis. Additionally, a control group comprising 100 DNA samples from individuals with normal spermogram and testing negative for CT was included in the study. The PCR-sequencing for detecting the 2-nt deletion of the second exon of the DEFB126 was performed.

Results

The Chi-squared test comparing all three groups revealed no significant difference across the different genotypes. Moreover, no significant difference between the symptomatic and asymptomatic groups was seen. However, analysis within CT-positive patients and controls demonstrated significant difference between the frequencies of homozygous del/del.

Conclusion

The higher frequency of the 2-nt deletion of the DEFB126 in CT- positive patients suggests that the occurrence of mutations in the DEFB-126 may cause the impairment of the antimicrobial activity of the DEFB126 protein and consequently makes individuals more susceptible to infections such as CT.

Two World Wars and Belgium: Missing Births and Birth Sex Ratio Changes

INTRODUCTION

The sex ratio at birth (male/total births, M/T) is expected to approximate 0.515. M/T is influenced by many factors including stress. Both World Wars have been implicated as influencing birth rates and M/T. This study was carried out to analyse the effects of two World Wars on Belgium vis-à-vis missing births as well as M/T changes.

METHODS

Belgian male and female births were available for 1830-2019 and annual population was available from Statista. ARIMA models were used to estimate and project birth losses. The effect of wars was assumed to begin in the years following the commencement of each war and extend to the year after cessation of hostilities i.e., 1915-1919 and 1940-1946 for the First and Second World Wars respectively.

RESULTS

This study included 27,346,178 live births for 1830-2019, M/T 0.5124. There was a decreasing trend in births for 1830-2019, significant for 1950-2019. There were dips in births in association with both Wars resulting in over 440,000 missing births, 3.80% of the Belgian population for the First World War and 1.91% for the Second World War. M/T rose non-significantly for the First World War and significantly for the Second World War.

DISCUSSION

The declining birth rate and M/T in developed countries is a recognised phenomenon. The missing births in relation to wars are of demographic importance but are often overlooked with emphasis usually on casualties and deaths. M/T may rise in wars, possibly due to increased coital activity as well as other factors.

Effects of cigarette smoking on semen quality, reproductive hormone levels, metabolic profile, zinc and sperm DNA fragmentation in men: results from a population-based study

Background

Cigarette smoking seems to have a negative impact on men's reproductive health, but our knowledge of its effects on the reproductive function of Russian men is still very limited. The purpose of this study was to evaluate the effect of cigarette smoking on semen quality, including sperm DNA fragmentation, hormonal, zinc and metabolic status in young men from the general multi-ethnic Russian population (n=1,222, median age 23 years) and to find out the ethno-specific effects of smoking by comparing male groups of different ethnicity.

Methods

Each participant filled out a standardized questionnaire, provided one blood and semen sample. Semen parameters, serum reproductive hormones, lipids, glucose, uric acid and seminal zinc were analyzed. Participants were classified as smokers (n=450) and non-smokers (n=772), and smokers were stratified into moderate (≤10 cigarettes/day) and heavy (>10 cigarettes/day) smokers.

Results

In the entire study population, heavy smokers were characterized by a decrease in semen volume, total sperm count, sperm concentration and motility, and an increase in sperm DNA fragmentation and teratozoospermia compared with non-smokers (p<0.05). There was also a reduction in the serum and seminal zinc level as well as an impairment in metabolic health in smokers compared with non-smokers (p<0.05). No significant differences between smokers and non-smokers were found for serum levels of LH, FSH, inhibin B, testosterone and estradiol. In the second part of our study, the most numerous ethnic groups of Slavs (n=654), Buryats (n=191), and Yakuts (n=125) were selected from the entire study population. Among three ethnic groups, the smoking intensity was higher in Slavs than in Buryats or Yakuts suggesting a greater tobacco addiction in Slavs than in Asians. A decrease in semen parameters and seminal zinc levels, and an increase in sperm DNA fragmentation and teratozoospermia was observed only in smoking Slavs (p<0.05); moderate decrease in testosterone and increase in triglyceride levels were revealed in smoking Yakuts (p<0.05), but no significant changes were detected in smoking Buryats.

Conclusion

We concluded that cigarette smoking has an ethno-specific effect on male reproductive function, probably due to the different activity of the seminal antioxidant system, which is yet to be elucidated.

Male reproductive ageing: a radical road to ruin

In modern post-transition societies, we are reproducing later and living longer. While the impact of age on female reproductive function has been well studied, much less is known about the intersection of age and male reproduction. Our current understanding is that advancing age brings forth a progressive decline in male fertility accompanied by a reduction in circulating testosterone levels and the appearance of age-dependent reproductive pathologies including benign prostatic hypertrophy and erectile dysfunction. Paternal ageing is also associated with a profound increase in sperm DNA damage, the appearance of multiple epigenetic changes in the germ line and an elevated mutational load in the offspring. The net result of such changes is an increase in the disease burden carried by the progeny of ageing males, including dominant genetic diseases such as Apert syndrome and achondroplasia, as well as neuropsychiatric conditions including autism and spontaneous schizophrenia. The genetic basis of these age-related effects appears to involve two fundamental mechanisms. The first is a positive selection mechanism whereby stem cells containing mutations in a mitogen-activated protein kinase pathway gain a selective advantage over their non-mutant counterparts and exhibit significant clonal expansion with the passage of time. The second is dependent on an age-dependent increase in oxidative stress which impairs the steroidogenic capacity of the Leydig cells, disrupts the ability of Sertoli cells to support the normal differentiation of germ cells, and disrupts the functional and genetic integrity of spermatozoa. Given the central importance of oxidative stress in defining the impact of chronological age on male reproduction, there may be a role for antioxidants in the clinical management of this process. While animal studies are supportive of this strategy, carefully designed clinical trials are now needed if we are to realize the therapeutic potential of this approach in a clinical context.

Male infertility

Clinical infertility is the inability of a couple to conceive after 12 months of trying. Male factors are estimated to contribute to 30-50% of cases of infertility. Infertility or reduced fertility can result from testicular dysfunction, endocrinopathies, lifestyle factors (such as tobacco and obesity), congenital anatomical factors, gonadotoxic exposures and ageing, among others. The evaluation of male infertility includes detailed history taking, focused physical examination and selective laboratory testing, including semen analysis. Treatments include lifestyle optimization, empirical or targeted medical therapy as well as surgical therapies that lead to measurable improvement in fertility. Although male infertility is recognized as a disease with effects on quality of life for both members of the infertile couple, fewer data exist on specific quantification and impact compared with other health-related conditions.

Evaluation of Sperm DNA Fragmentation Using Two Different Methods: TUNEL via Fluorescence Microscopy, and Flow Cytometry

Background and Objectives: Sperm DNA fragmentation refers to any break in one or both of the strands of DNA in the head of a sperm. The most widely used methodologies for assessing sperm DNA fragmentation are the sperm chromatin structure assay (SCSA), the sperm chromatin dispersion assay (SCD), the single-cell gel electrophoresis assay (SCGE-comet), and the terminal-deoxynucleotidyl-transferase (TdT)-mediated dUTP nick end labelling (TUNEL) assay. The aim of this study was to compare the efficiency and sensitivity of the analysis of sperm DNA fragmentation using TUNEL via fluorescence microscopy, and flow cytometry. Materials and Methods: Semen samples were collected and analyzed for standard characteristics using light microscopy, and for sperm DNA fragmentation using both TUNEL via fluorescence microscopy, and flow cytometry. Results: There were no significant differences in the values of the sperm DNA fragmentation index (DFI) obtained when the analysis was performed using TUNEL or flow cytometry (p = 0.543). Spearman's correlation analysis revealed a significant negative correlation between sperm motility (%) and sperm DNA fragmentation (p < 0.01), as well as between sperm concentration and sperm DNA fragmentation (p < 0.05). The Mann-Whitney U test showed no significant difference in the DFI among couples with repeated implantation failure (RIF) and miscarriages (p = 0.352). Conclusions: Both methods (TUNEL via fluorescence microscopy, and flow cytometry) have a high efficiency and sensitivity in accurately detecting sperm DNA fragmentation, and can be effectively used to assess male fertility.

Role of oxidative stress in male infertility

Abstract

Infertility affects millions of couples worldwide. Oxidative stress (OS) causes peroxidation of lipids and damage to spermatozoa, thus, reducing the quality of seminal parameters. In addition, the differences in the levels of antioxidants and reactive oxygen species (ROS) caused by intrinsic and extrinsic variables linked to lifestyle, diet, genetics, and OS also contribute to male infertility. High levels of ROS result in sperm damage of sperm parameters due to lipid peroxidation and oxidation of proteins. Other significant causes of ROS include changes in sex hormone levels, sperm DNA damage, including mutations, and immature spermatozoa. Treating the root causes of OS, by changing one's lifestyle, as well as antioxidant therapy, may be helpful strategies to fight OS-related infertility. However, the determination of male infertility induced by OS is currently a challenge in the field of reproductive health research. This review intends to describe the role of oxidative stress on male infertility and the current understanding of its management.

Lay summary

The inability to conceive affects many couples globally. Oxidative stress refers to imbalances between different oxygen species which can lead to male fertility problems by damaging sperm and semen. Oxidative stress may be caused by several factors, including diets high in fats, sugars and processed foods, lifestyle (including smoking, alcohol consumption and having a sedentary lifestyle), and genetics. Treatment that focuses on the root cause may help combat male infertility. However, there is currently no consensus on the best way to treat male fertility problems, particularly those associated with oxidative stress. This paper describes the role of oxidative stress on male infertility and discusses the current techniques employed in treating male fertility issues.

State-specific fertility rate changes across the USA following the first two waves of COVID-19

STUDY QUESTION

How did the first two coronavirus disease 2019 (COVID-19) waves affect fertility rates in the USA?

SUMMARY ANSWER

States differed widely in how their fertility rates changed following the COVID-19 outbreak and these changes were influenced more by state-level economic, racial, political, and social factors than by COVID-19 wave severity.

WHAT IS KNOWN ALREADY

The outbreak of the COVID-19 pandemic contributed to already declining fertility rates in the USA, but not equally across states. Identifying drivers of differential changes in fertility rates can help explain variations in demographic shifts across states in the USA and motivate policies that support families in general, not only during crises.

STUDY DESIGN, SIZE, DURATION

This is an ecological study using state-level data from 50 US states and the District of Columbia (n = 51). The study period extends from 2020 to 2021 with historical data from 2016 to 2019. We identified Wave 1 as the first apex for each state after February 2020 and Wave 2 as the second apex, during Fall/Winter 2020-2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

State-level COVID-19 wave severity, defined as case acceleration during each 3-month COVID-19 wave (cases/100 000 population/month), was derived from 7-day weekly moving average COVID-19 case rates from the US Centers for Disease Control and Prevention (CDC). State-level fertility rate changes (change in average monthly fertility rate/100 000 women of reproductive age (WRA)/year) were derived from the CDC Bureau of Vital Statistics and from 2020 US Census and University of Virginia 2021 population estimates 9 months after each COVID-19 wave. We performed univariate analyses to describe national and state-level fertility rate changes following each wave, and simple and multivariable linear regression analyses to assess the relation of COVID-19 wave severity and other state-level characteristics with fertility rate changes.

MAIN RESULTS AND THE ROLE OF CHANCE

Nationwide, fertility dropped by 17.5 births/month/100 000 WRA/year following Wave 1 and 9.2 births/month/100 000 WRA/year following Wave 2. The declines following Wave 1 were largest among majority-Democrat, more non-White states where people practiced greater social distancing. Greater COVID-19 wave severity was associated with steeper fertility rate decline post-Wave 1 in simple regression, but the association was attenuated when adjusted for other covariates. Adjusting for the economic impact of the pandemic (hypothesized mediator) also attenuated the effect. There was no relation between COVID-19 wave severity and fertility rate change following Wave 2.

LIMITATIONS, REASONS FOR CAUTION

Our study harnesses state-level data so individual-level conclusions cannot be inferred. There may be residual confounding in our multivariable regression and we were underpowered to detect some effects.

WIDER IMPLICATIONS OF THE FINDINGS

The COVID-19 pandemic initially impacted the national fertility rate but, overall, the fertility rate rebounded to the pre-pandemic level following Wave 2. Consistent with prior literature, COVID-19 wave severity did not appear to predict fertility rate change. Economic, racial, political, and social factors influenced state-specific fertility rates during the pandemic more than the severity of the outbreak alone. Future studies in other countries should also consider whether these factors account for internal heterogeneity when examining the impact of the COVID-19 pandemic and other crises on fertility.

STUDY FUNDING/COMPETING INTEREST(S)

L.G.K. received funding from the National Institute of Environmental Health Sciences (R00ES030403), M.C. from the National Science Foundation Graduate Research Fellowship Program (20-A0-00-1005789), and M.L. and E.S. from the National Institute of Environmental Health Sciences (R01ES032808). None of the authors have competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Contraception ends the genetic maintenance of human same-sex sexual behavior

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Circadian desynchrony disturbs the function of rat spermatozoa

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