Charalampos Tsimpoukelis

Background/Objectives: Recurrent implantation failure (RIF) affects many women undergoing IVF, but its genetic basis remains poorly defined. Most studies linking genetic or chromosomal factors to RIF were conducted before preimplantation genetic testing for aneuploidy (PGT-A) was widely used, when embryonic aneuploidy could not be reliably excluded. This review asks whether that evidence still holds now that PGT-A allows embryo aneuploidy to be excluded, at least analytically, as the default explanation for failed transfers. Methods: We reviewed the literature on parental karyotype abnormalities, chromosomal microarray findings, thrombophilia-related gene variants, and endometrial receptivity testing in women with RIF, comparing pre-PGT-A and post-PGT-A era studies where available. Results: Most foundational data on RIF genetics predate PGT-A and likely overstate the embryo’s contribution to implantation failure relative to maternal factors. Very few studies have re-evaluated RIF using strict, PGT-A-confirmed criteria for “true” implantation failure. Evidence for thrombophilia gene variants remains inconsistent across populations, and endometrial receptivity testing still lacks well-established genetic correlates. Conclusions: The genetic evidence base for RIF needs updating for the PGT-A era. A clear, PGT-A-confirmed picture of the genetic and chromosomal contributors to true implantation failure is still missing. Closing this gap should be a priority for future research in reproductive genetics.

Obesity affects nearly one in three women of reproductive age worldwide and consistently reduces success rates in in vitro fertilization, yet the molecular basis for this reduction remains fragmented across separate lines of evidence. Circadian clock genes, particularly BMAL1, orchestrate metabolic and reproductive physiology through transcription–translation feedback loops present in adipose tissue, ovarian granulosa cells, and endometrial stroma. Adiposity-driven metabolic shifts, including altered PPAR-γ signaling and reduced glutamine–methionine uptake, degrade BMAL1 expression and flatten its rhythmic oscillation in peripheral tissues. Within granulosa cells, loss of BMAL1 rhythmicity impairs mitochondrial biogenesis and disrupts UPRmt-mediated proteostasis, driving reactive oxygen species accumulation and compromising oocyte competence. Parallel disruption of clock-controlled transcription factors in endometrial epithelium and stroma is proposed to alter decidualization programs and displace the window of implantation, which would produce a receptivity defect independent of oocyte quality if confirmed directly in human tissue. Clinical data are consistent with a dual mechanism: obese women undergoing donor-oocyte cycles—where oocyte quality is controlled for—show reduced implantation rates in several but not all cohorts—a pattern compatible with an endometrial contribution distinct from oocyte-level damage, rather than proof of it. Synthesizing evidence from adipocyte biology, ovarian physiology, and endometrial receptivity research drawn largely from rodent models, cultured cell systems, and observational human cohorts, this review proposes BMAL1 dysregulation as a candidate unifying mechanism connecting obesity to impaired IVF outcomes at the gametic and uterine level, while acknowledging that direct causal evidence in humans is still lacking. Chronotherapeutic strategies, including melatonin supplementation and the timing of weight-loss interventions relative to ovarian stimulation, are discussed as hypotheses for future testing rather than current clinical recommendations. BMAL1 dysregulation is presented here as one candidate contributor among several interacting mechanisms, and any translational strategy would need to be part of a broader, coordinated approach to obesity-related IVF failure rather than a stand-alone intervention.

Endocrine disorders and inherent flaws in oocyte quality are traditional causes of female infertility. Increasing research indicates that structural and biomechanical alterations in the ovarian microenvironment may significantly contribute to reproductive decline. Progressive extracellular matrix remodeling, stromal fibrosis, chronic inflammation, and heightened tissue stiffness seem to affect follicular homeostasis, granulosa–oocyte communication, and ovarian function. Fibro-inflammatory pathways, including transforming growth factor-β (TGF-β), Hippo/YAP-TAZ signaling, oxidative stress, macrophage activation, and mechanotransduction, are increasingly associated with ovarian ageing, polycystic ovary syndrome, reduced ovarian reserve, and unfavourable reproductive outcomes. Here, the term ‘fibro-inflammatory ovary’ is used descriptively to unify these mechanisms rather than as an established clinical entity. Mechanical alterations of the ovarian stroma may affect follicular activation, vascularization, and oocyte competence by altering cellular tension and extracellular matrix dynamics. Our review examines growing findings about ovarian fibrosis and stromal remodeling in female infertility, focusing on molecular causes, mechanobiology, and translational implications for assisted reproduction. Potential diagnostic uses, such as ovarian elastography, and prospective anti-fibrotic therapy techniques are also examined.

Endometriosis affects approximately 10% of women of reproductive age and is associated with infertility in up to half of those diagnosed. Despite decades of research, the molecular basis of its reproductive consequences remains poorly defined. Among the pathophysiological features most consistently documented in affected women, chronic oxidative stress within the peritoneal cavity has attracted sustained attention, yet its relationship to the extracellular vesicle biology that has emerged as central to endometriosis pathogenesis has never been systematically examined. Iron-catalyzed radical chemistry, macrophage-derived superoxide, and mitochondrial electron leak in ectopic stromal cells collectively sustain a peritoneal redox burden that modifies exosomal biogenesis, alters microRNA sorting, and reprograms vesicle lipid and protein cargo. Oxidatively conditioned exosomes skew peritoneal macrophages toward an immunosuppressive M2 phenotype through miR-301a-3p, miR-146a-5p, and miR-196a-5p, suppress natural killer cell cytotoxicity through NKG2D ligand decoy delivery, facilitate peritoneal dissemination and neuroangiogenesis, and compromise oocyte developmental competence through ferroptosis-derived vesicles carrying aberrant miR-122-5p, oxidized phosphatidylethanolamines, and damaged mitochondria. These mechanisms map directly onto the clinical deficits observed in women with endometriosis undergoing assisted reproduction, including reduced oocyte yield, lower fertilization rates, elevated embryo aneuploidy, and impaired implantation. Follicular and peritoneal fluid exosomal microRNA profiles represent promising non-invasive biomarkers, while combinatorial strategies targeting the iron-ROS-exosome axis offer a more coherent therapeutic framework than the single-antioxidant approaches that have so far shown limited benefit.

Recurrent pregnancy loss (RPL) continues to be a significant challenge in reproductive medicine, particularly in women for whom standard examinations do not reveal a conclusive underlying reason. There is growing evidence that several instances may result from nuanced alterations in the endometrial milieu, particularly with decidualization and maternal–fetal immune tolerance. In recent years, vitamin D has gained recognition for its significance in early pregnancy, serving not only as a regulator of calcium metabolism but also as an active contributor to endometrial and immunological functions. The human endometrium exhibits the vitamin D receptor (VDR) and the enzyme CYP27B1, facilitating the local activation and signaling of vitamin D inside the uterine milieu. Experimental investigations have shown that vitamin D influences many processes critical for effective implantation and placentation, including stromal cell differentiation, cytokine equilibrium, trophoblast invasion, oxidative stress responses, and immune cell communication. Aberrant vitamin D signaling has been associated with heightened inflammatory activity, impaired decidual transformation, altered uterine natural killer cell functionality, and alteration of the Treg/Th17 equilibrium, all of which have been implicated in recurrent pregnancy loss. Concurrently, there is an increasing emphasis on the association between vitamin D and mitochondrial function as well as oxidative stress in decidual and endometrial cells. Interruption of these pathways may influence implantation and early embryonic development by impacting cellular metabolism and immunological control at the maternal–fetal interface. The clinical interest in vitamin D supplementation for women experiencing repeated reproductive failure is increasing; nevertheless, the existing results are conflicting, mostly due to the predominance of research focusing on circulating vitamin D levels rather than localized tissue-specific processes. Our review encapsulates new findings about the function of vitamin D in endometrial biology and reproductive immune regulation, emphasizing its involvement in decidualization, inflammatory signaling, oxidative stress, and maternal–fetal immunological tolerance in recurrent pregnancy loss. The potential ramifications for assisted reproduction and forthcoming tailored therapy techniques are also examined.

A significant concern with IVF is that many embryos fail to develop despite proper fertilization. This gap indicates that factors outside sperm-oocyte fusion influence developmental competency. The maternal-zygotic transition (MZT) is a crucial developmental phase during which control shifts from maternally inherited transcripts to activation of the embryonic genome. During the early stages following fertilization, the embryo depends only on maternal mRNA and proteins amassed throughout oogenesis. For successful development, these transcripts must be expeditiously removed with the concurrent genome activation. Any disruption, whether due to inadequate maternal mRNA degradation, aberrant translational control, or delayed genome activation, has been associated with premature developmental stoppage and diminished blastocyst formation. Principal regulators, such as BTG4, CPEB1, DAZL, and components of the translational machinery, govern this modification and seem to be affected by the quality of the oocyte and the age of the mother. Increasing evidence suggests that disruption of MZT may account for instances of suboptimal embryo development that conventional assessment techniques cannot elucidate. MZT offers a biological framework for assessing embryo competency beyond simple appearance. If scientists had a deeper understanding of this process, they might identify molecular markers and enhance the selection of embryos in IVF.

Oxidative stress is a fundamental mechanism that impacts reproductive function by altering gamete quality, fertilisation, and the initial development of embryos. Excessive reactive oxygen species lead to the oxidation of polyunsaturated fatty acids in the cell membranes of sperm, oocytes, and adjacent somatic cells. F2-isoprostanes and isofurans are two of the most dependable indicators of oxidative lipid damage among the byproducts generated during free radical-mediated lipid oxidation. Both arise from the non-enzymatic peroxidation of arachidonic acid and provide a chemically stable depiction of in vivo oxidative processes. Reproductive studies indicate that elevated levels of F2-isoprostanes are associated with diminished sperm motility, compromised membrane stability, and an increased risk of DNA fragmentation in various forms of male infertility. Lipid peroxidation products have been detected in follicular fluid inside the female reproductive system, suggesting a relationship between oxidative imbalance, granulosa cell metabolism, and oocyte competency. Isofurans, which are more prevalent in the presence of elevated oxygen levels, may indicate oxidative stress in mitochondria and complications with cellular respiration. The current comprehension of lipid peroxidation indicators in infertility and assisted reproduction remains insufficient. This review aims to synthesise current information on isoprostanes and isofurans as reliable indicators of oxidative lipid damage in reproductive biology, highlighting their effects on gamete quality, mitochondrial dysfunction, and results in assisted reproduction. Our research seeks to clarify the biological importance of current experimental and clinical findings, highlighting their potential as clinically relevant biomarkers in reproductive medicine.

Infertility and ovarian ageing are increasingly acknowledged as illnesses affected not just by endocrine decline but also by chronic inflammatory stress and mitochondrial dysfunction in the reproductive milieu. The cGAS-STING signalling pathway has emerged as a significant possibility linking these activities. The cGAS-STING pathway, originally defined as a cytosolic DNA-sensing mechanism essential for innate immune defence, is now recognised as a broader modulator of sterile inflammation, cellular senescence, and tissue failure. Experimental reproductive models suggest that the activation of this system may operate as a crucial link between mitochondrial dysfunction, cytosolic DNA accumulation, inflammatory cytokine production, and the progressive decline of ovarian and endometrial function. The activation of cGAS-STING in granulosa cells has been associated with inflammatory signalling and impaired steroidogenic activity.

Conventional hormonal and clinical models inadequately clarify the complex and diverse aspects of female infertility, resulting in poor reproductive outcomes and reduced egg viability. A growing body of research indicates that female reproductive failure is mostly due to disruptions in cellular homeostasis, especially concerning organelle quality control. Oxidative stress has emerged as a crucial mediator connecting metabolic, inflammatory, and ageing-related processes to ovarian failure, however its downstream impacts on intracellular organelle turnover remain insufficiently clarified. Our narrative review encapsulates the existing data for a unified pathogenic concept focused on the redox-regulated mitochondria–lysosome axis. We examine the interaction of oxidative stress, mitochondrial malfunction, compromised mitophagy, and lysosomal deficiency in granulosa cells and oocytes. Prolonged oxidative stress may disrupt this equilibrium, leading to defective mitochondria accumulation and impaired mitophagy. This self-perpetuating cycle may ultimately jeopardises reproductive viability and oocyte integrity. The integrated axis offers a shared molecular foundation for various infertility-related diseases, such as inadequate ovarian response, obesity-associated infertility, polycystic ovary syndrome, and ovarian ageing. Ultimately, we analyse new findings suggesting that specific antioxidant chemicals modify mitophagy and lysosomal function while also neutralising reactive oxygen species, highlighting their potential use in precision fertility treatments. Our research redefines female infertility as a condition of redox-dependent organelle quality control, thereby introducing novel avenues for identifying biomarkers, categorising patients, and targeting treatments in assisted reproduction.

Oocyte competency is a crucial determinant of fertilisation success and the initial development of embryos in assisted reproductive technologies. The metabolic and biochemical environment of the ovarian follicle is crucial for determining oocyte developmental potential, alongside genetic integrity. The follicular microenvironment includes a complex network of signalling chemicals that regulate mitochondrial activity, steroidogenesis, oxidative balance, and cellular energy metabolism. Recently, metabolic hormones originating from adipose tissue and skeletal muscle, namely, adipokines and myokines, have received considerable focus as crucial regulators of ovarian physiology. Adiponectin, irisin, and the recently identified hormone asprosin have emerged as crucial metabolic regulators influencing granulosa cell activity, mitochondrial bioenergetics, insulin signalling pathways, and redox homeostasis inside the follicular niche. Adiponectin mostly provides metabolic protection by activating AMP-activated protein kinase (AMPK) and improving insulin sensitivity, which in turn enhances mitochondrial efficiency and steroidogenic function in granulosa cells. Irisin, derived from the breakdown of fibronectin type III domain-containing protein 5 (FNDC5), aids the developing oocyte by facilitating mitochondrial biogenesis, augmenting oxidative phosphorylation, and altering cellular defence mechanisms against oxidative stress. Conversely, asprosin has been associated with glucogenic signalling, metabolic stress, and probable mitochondrial malfunction, suggesting a possible relationship between systemic metabolic problems and negative reproductive consequences. Clinical and experimental research indicate that the levels of these metabolic regulators in follicular fluid may correlate with ovarian response, oocyte quality, fertilisation rates, and embryo development during in vitro fertilisation cycles. This review consolidates current molecular, cellular, and clinical information, clarifying the pathways by which adipokines and myokines influence follicular metabolism and impact oocyte competency. Understanding the metabolic connections between systemic endocrine signals and the follicular milieu may provide novel indicators for reproductive prognosis and provide new treatment targets to improve assisted reproduction outcomes.