Age- and endometrial microbiota-related delay in development of endometrial receptivity

Microbiome-Maternal Tract Interactions in Women with Recurrent Implantation Failure

Microorganisms play an important role in regulating various biological processes in our bodies. In women, abnormal changes in the reproductive tract microbiome are associated with various gynecological diseases and infertility. Recent studies suggest that patients with recurrent implantation failure (RIF) have a reduced genus Lactobacillus population, a predominant bacterial species in the vagina and uterus that protects the reproductive tract from pathogenic bacterial growth via the production of various metabolites (e.g., lactic acid, bacteriocin, and H2O2). Moreover, a higher percentage of pathogenic bacteria genera, including Atopobium, Gardnerella, Prevotella, Pseudomonas, and Streptococcus, was found in the uterus of RIF patients. This review aimed to examine the role of pathogenic bacteria in RIF, determine the factors altering the endometrial microbiome, and assess the impact of the microbiome on embryo implantation in RIF. Several factors can influence microbial balance, including the impact of extrinsic elements such as semen and antibiotics, which can lead to dysbiosis in the female reproductive tract and affect implantation. Additionally, probiotics such as Lacticaseibacillus rhamnosus were reported to have clinical potential in RIF patients. Future studies are needed to develop targeted probiotic therapies to restore microbial balance and enhance fertility outcomes. Research should also focus on understanding the mechanisms by which microorganisms generate metabolites to suppress pathogenic bacteria for embryo implantation. Identifying these interactions may contribute to innovative microbiome-based interventions for reproductive health.

Uterine Microbiota and Bisphenols: Novel Influencers in Reproductive Health

Infertility affects 8-12% of couples worldwide, and 30-75% of preclinical pregnancy losses are due to a failure during the implantation process. Exposure to endocrine disruptors, like bisphenols, among others, has been associated with the increase in infertility observed in the past decades. An increase in infertility has correlated with exposure to endocrine disruptors like bisphenols. The uterus harbors its own microbiota, and changes in this microbiota have been linked to several gynecological conditions, including reproductive failure. There are no studies on the effects of bisphenols on the uterine-microbiota composition, but some inferences can be gleaned by looking at the gut. Bisphenols can alter the gut microbiota, and the molecular mechanism by which gut microbiota regulates intestinal permeability involves Toll-like receptors (TLRs) and tight junction (TJ) proteins. TJs participate in embryo implantation in the uterus, but bisphenol exposure disrupts the expression and localization of TJ proteins. The aim of this review is to summarize the current knowledge on the microbiota of the female reproductive tract (FRT), its association with different reproductive diseases-particularly reproductive failure-the effects of bisphenols on microbiota composition and reproductive health, and the molecular mechanisms regulating uterine-microbiota interactions crucial for embryo implantation. This review also highlights existing knowledge gaps and outlines research needs for future risk assessments regarding the effects of bisphenols on reproduction.

Factors influencing endometrial receptivity in women with recurrent implantation failure

BACKGROUND

Embryo implantation involves two key elements: a good quality embryo and receptive endometrium. Endometrial receptivity abnormalities are known as one of the possible causes of recurrent implantation failure (RIF), especially when the embryo is euploid. This study was aimed to evaluate the impact of age and other clinical factors on endometrial receptivity in women with RIF.

METHODS

68 women with RIF (defined as at least three unsuccessful transfers of good quality embryo of at least 1BB category of blastocysts) and 49 controls (women undergoing IVF treatment because of idiopathic infertility or male factor) were included to the study. After preparation of the endometrium by the hormone replacement therapy endometrial biopsies were taken from each patient and sequenced with beREADY test TAC targeting 67 biomarker genes for endometrial receptivity. Depending on the test result patients were classified into one of four different groups: pre-receptive (n = 16), early-receptive (n = 54), receptive (n = 44) and late-receptive (n = 3).

RESULTS

In women with RIF pre-receptive endometrium has been detected substantially more often than in controls - 13 (19,1%) vs. 3 (6,1%) patients (p = 0,043). Early-receptive endometrium was diagnosed in the majority of patients with idiopathic infertility - 12 (66.7%) vs. 6 (33.3%) women (p = 0.042) and with polycystic ovary syndrome (PCOS) - 12 (70,6%) vs. 3 (17.7%) women (p = 0,0447). We found significant association between abnormal endometrial receptivity and patient's age and duration of infertility. Young women were diagnosed significantly more often as normal or late-receptive, whereas older women with longer history of infertility as early-receptive and pre-receptive.

CONCLUSIONS

In patients with RIF in comparison to other women undergoing IVF procedures, patient's age and infertility duration are the most important factors related to endometrial receptivity abnormalities, indicating that older women with a longer history of infertility may benefit the most from endometrial receptivity testing.

TRIAL REGISTRATION

Not applicable.

Hallmarks of female reproductive aging in physiologic aging mice

The female reproductive axis is one of the first organ systems to age, which has consequences for fertility and overall health. Here, we provide a comprehensive overview of the biological process of female reproductive aging across reproductive organs, tissues and cells based on research with widely used physiologic aging mouse models, and describe the mechanisms that underpin these phenotypes. Overall, aging is associated with dysregulation of the hypothalamic-pituitary-ovarian axis, perturbations of the ovarian stroma, reduced egg quantity and quality, and altered uterine morphology and function that contributes to reduced capacity for fertilization and impaired embryo development. Ultimately, these age-related phenotypes contribute to altered pregnancy outcomes and adverse consequences in offspring. Conserved mechanisms of aging, as well as those unique to the reproductive system, underlie these phenotypes. The knowledge of such mechanisms will lead to development of therapeutics to extend female reproductive longevity and support endocrine function and overall health.

Age-related uterine changes and its association with poor reproductive outcomes: a systematic review and meta-analysis

BACKGROUND

The decline in women's fertility becomes clinically relevant between 35-40 years old, when there is insufficient ovarian activity, and it becomes more difficult to achieve pregnancy naturally and through artificial reproductive technologies. A competent endometrium is required for establishing and maintaining a pregnancy to term, however, experts in the field underestimate the contribution of endometrial age and its impact on reproductive outcomes remains unclear.

STUDY DESIGN

A systematic search of full-text articles available in PubMed was conducted to retrieve relevant studies published until March 2023. Search terms included: endometrium, uterus, age, aging, pregnancy, and oocyte donation. Terms related to reproductive pathologies were excluded. Eligibility criteria included original, rigorous, and accessible peer-reviewed work, published in English on the effect of age on the uterus and endometrium.

RESULTS

From 11,354 records identified, 142 studies were included for systematic review, and 59 were eligible for meta-analysis of endometrial thickness (n = 7), pregnancy rate (n = 22), implantation rate (n = 10), live birth rate (n = 10) and pregnancy loss rate (n = 11). Studies for the meta-analysis of reproductive outcomes only included transfers of embryos from ovum donation (ovum donors < 36 years old). Age shrinks the uterus; depletes endometrial blood supply through narrow uterine veins and a progressive loss of uterine spiral arteries; disrupts endometrial architecture and cellular composition; alters hormone production, shortening menstrual cycle length and impeding endometrial progression to the secretory stage; and dysregulates key endometrial functions such as adhesion, proliferation, apoptosis, and receptivity, among others. Women over 35-40 years old had significantly thinner endometrium (MD 0.52 mm). Advanced maternal age is associated with lower odds of achieving implantation (27%) and clinical pregnancy (20%), or higher odds of experiencing pregnancy loss (44%).

CONCLUSION

Due to the effect of age on endometrium reported in this review, managing patients with advanced maternal age may require considering the endometrial factor as a potential tissue to treat with anti-aging strategies. This review provides researchers and clinicians with an updated and in-depth summary of this topic, encouraging the development of new tailored anti-aging and preventive strategies for precision medicine in endometrial factor in infertility.

TRIAL REGISTRATION

PROSPERO 2023 (CRD42023416947).

Mechanisms of endometrial aging: lessons from natural conceptions and assisted reproductive technology cycles

Until recently, the study of age-related decline in fertility has focused primarily on the ovary; depletion of the finite pool of oocytes and increases in meiotic errors leading to oocyte aneuploidy are well-established mechanisms by which fertility declines with advancing age. Comparatively little is known about the impact of age on endometrial function. The endometrium is a complex tissue comprised of many cell types, including epithelial, stromal, vascular, immune and stem cells. The capacity of this tissue for rapid, cyclic regeneration is unique to this tissue, undergoing repeated cycles of growth and shedding (in the absence of an embryo) in response to ovarian hormones. Furthermore, the endometrium has been shown to be capable of supporting pregnancies beyond the established boundaries of the reproductive lifespan. Despite its longevity, molecular studies have established age-related changes in individual cell populations within the endometrium. Human clinical studies have attempted to isolate the effect of aging on the endometrium by analyzing pregnancies conceived with euploid, high quality embryos. In this review, we explore the existing literature on endometrial aging and its impact on pregnancy outcomes. We begin with an overview of the principles of endometrial physiology and function. We then explore the mechanisms behind endometrial aging in its individual cellular compartments. Finally, we highlight lessons about endometrial aging gleaned from rodent and human clinical studies and propose opportunities for future study to better understand the contribution of the endometrium to age-related decline in fertility.

The number of previous implantation failures is a critical determinant of intrauterine autologous platelet-rich plasma infusion success in women with recurrent implantation failure

Purpose

We aimed to identify factors influencing the reproductive outcomes of frozen-thawed embryo transfer (FET) with intrauterine autologous platelet-rich plasma (PRP) infusion in patients with either a thin endometrium or recurrent implantation failure (RIF) despite a normal endometrial appearance.

Methods

In this retrospective study of women who underwent PRP-FET, factors influencing PRP-FET outcomes were identified using multivariate logistic regression analysis.

Results

We enrolled 111 patients (70 with refractory thin endometrium and 41 with RIF but no thin endometrium). For 99 completed FET cycles, the β-hCG positivity rate was 46.7%, clinical pregnancy rate (CPR) was 41.0%, and live birth rate (LBR) was 36.2%. PRP treatment was associated with significant improvements over previous cycles, and participants with thin endometria demonstrated thickening. Multivariate logistic regression analysis showed that the number of previous implantation failures in women with RIF was a significant factor affecting the PRP-FET outcomes. The CPR and LBR of women with RIF were lower when there had been ≥3 previous implantation failures occurred.

Conclusions

Intrauterine PRP infusion improves the pregnancy outcomes of patients with RIF or a thin endometrium. The number of previous implantation failures is a critical determinant of successful intrauterine PRP infusions in women with RIF.