Endometrial aging and female fertility: Molecular mechanisms, clinical consequences and therapeutic opportunities

INTRODUCTION

For more than three decades, the prevailing view in reproductive medicine has been that the uterus does not age. This paradigm originated from the preliminary oocyte-donation report by Sauer and colleagues, in which seven women aged 40–44 years with ovarian failure who received oocytes from young donors achieved pregnancies at rates comparable to those reported in younger recipients. These findings led to the conclusion that maternal age primarily affects oocyte quality rather than uterine receptivity.¹

Subsequent landmark studies appeared to reinforce this concept. Navot and colleagues, sharing oocytes from the same donors between younger and older recipients, reported preserved implantation in recipients up to the mid-forties and attributed the age-related decline in fertility to oocyte quality rather than to a diminished capacity of the uterus to sustain implantation.^2,3 Notably, Borini and colleagues demonstrated that successful pregnancies could be achieved in postmenopausal women over 50 years of age through oocyte donation, reporting clinical pregnancies in this age group and confirming that hormonal preparation of the endometrium could support implantation even beyond natural reproductive age.⁴ Abdalla and colleagues found no significant association between recipient age and pregnancy outcomes in donor cycles,⁵ while Noci and colleagues, in a morphological and immunohistochemical study, found no significant differences between the endometria of women under 30 and over 40 years of age and concluded that the human endometrium does not appear to age as long as cyclic hormonal stimulation and menstruation persist.⁶ Together, these reports established the concept of the “ageless uterus,” which for decades served as a clinical reassurance for women delaying motherhood (Table 1).

However, early signals challenging this paradigm emerged shortly thereafter. Flamigni et al. reported reduced pregnancy and implantation rates in older oocyte-donation recipients, with pregnancy rates declining from 45% in women aged 21–35 years to 23% in those aged 41–49 years, and implantation rates from 23% to 10%.⁷ The same dataset was subsequently discussed by Borini and Asch in a contemporaneous book chapter on factors affecting implantation in the human⁸; these two publications therefore represent a single body of evidence rather than independent confirmation. These observations were later corroborated by Borini et al. in a 1996 cohort study of recipients sharing oocytes from a single donor.⁹

In a provocative 1998 JARG editorial titled “The Uterus: Idiot Savant or Rosetta Stone?”, Glasser formally questioned whether the uterus itself undergoes aging,¹⁰ marking an important conceptual shift.

Since then, accumulating evidence has increasingly challenged the notion of an “ageless uterus.” Large donor-oocyte cohort studies, along with transcriptomic and single-cell analyses and mechanistic investigations of cellular senescence, now converge to demonstrate that the endometrium ages independently of oocyte quality. This aging process is associated with impaired implantation, increased pregnancy loss, and reduced live birth rates after age 40.

More recent donor-oocyte studies incorporating larger cohorts, detailed outcomes, and embryos of known ploidy provide the strongest support for this shift. Yeh and colleagues, analyzing 27,959 first fresh donor cycles in the United States, demonstrated a graded decline in live birth rates with increasing recipient age.¹¹ A subsequent SART registry analysis of 40,485 donor-oocyte cycles (2016–2018) confirmed a reduction in live birth with increasing recipient age after single embryo transfer, with adjusted odds ratios of 0.80 for ages 40–44, 0.77 for ages 45–49 and 0.65 for recipients over 49 years.¹² Most notably, the largest cohort to date by Sebastian-Leon and colleagues showed a decline in live birth rate from 45.8% at age 40 to 32.7% at age 50, accompanied by significant annual increases in implantation failure (4.2% per year) and pregnancy loss (3.2% per year) beyond age 40.¹³

Collectively, these data provide compelling evidence that endometrial aging independently contributes to reproductive outcomes (Table 1).

DEMOGRAPHIC CONTEXT: WHY ENDOMETRIAL AGING MATTERS NOW

The average age at first birth has risen across high-income countries over the past four decades. In the European Union, the mean age at first childbirth reached 29.7 years in 2022.¹⁴ In the United States, the proportion of first births to women aged 35 and older has more than tripled since 1990, and first births to women aged 40 and older have quadrupled.¹⁵ This demographic shift collides with biological reality. Fecundability begins to decline measurably in the early thirties and accelerates after age 35; natural conception rates fall to single digits per month after age 40.

Particularly noteworthy is the growing number of gestational surrogacy cycles undertaken by women of advanced age; including grandmothers, mothers, and other older relatives carrying pregnancies on behalf of family members. As surrogacy becomes more legally available across jurisdictions, gestational carriers of advanced reproductive age represent a distinct clinical population whose uterine biology warrants dedicated attention. The available literature on reproductive outcomes as a function of gestational carrier age is unfortunately very limited, and direct comparisons between age groups of proven carriers are sparse. This gap represents an important and underexplored area, as the uterine biology of a 45- or 50-year-old gestational carrier who has previously carried successful pregnancies may differ meaningfully from a nulliparous woman of similar age, yet current evidence is insufficient to guide age-specific counseling in this population.

Beyond demographics, egg freezing, oocyte donation, and gestational surrogacy have created a more flexible reproductive map, but they have not eliminated the underlying biology of uterine aging, and they have introduced new questions about how best to counsel women across the entire reproductive lifespan.

PATHOPHYSIOLOGY OF ENDOMETRIAL AGING

Endometrial aging is driven by the same fundamental biological mechanisms that underlie aging in other tissues, expressed in a uterus-specific context. The classical hallmarks of aging, including genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, dysbiosis, and impaired macroautophagy are now recognized to operate within the endometrium.¹⁶ (Table 2)

Oxidative Stress, Mitochondrial Dysfunction, and Telomere Attrition

Cellular aging in the endometrium is initiated by the convergence of three upstream stressors that progressively accumulate across menstrual cycles. Oxidative stress arises from the imbalance between reactive oxygen species (ROS) generation and antioxidant capacity. The cycling endometrium experiences repeated bursts of ROS during ovulation, menstrual shedding, and re-vascularization, and with age both ROS production rises and antioxidant defenses decline. Mitochondrial dysfunction is closely coupled to oxidative stress: with age, mitochondrial copy number declines, membrane potential is reduced, electron transport chain efficiency drops, and mitochondrial DNA acquires deletions and point mutations. Telomere attrition provides a third upstream driver; telomere shortening triggers the DNA damage response and irreversibly commits cells to senescence.^16,17

Cellular Senescence and the SASP

Cellular senescence is the irreversible cell-cycle arrest of cells that have accumulated unsustainable damage, enforced through the p16⁺INK4a-Rb and p21⁺Cip1-p53 pathways. In the endometrium, senescence has a dual nature: transient, controlled senescence is required for the inflammatory burst supporting embryo invasion, but when clearance by uterine natural killer cells becomes incomplete, as occurs with chronological aging and immunosenescence, the accumulated senescence-associated secretory phenotype (SASP) sustains chronic inflammation that disrupts cyclic remodeling and impairs angiogenesis. Lucas and colleagues demonstrated that women with recurrent pregnancy loss show a pro-senescent decidual response during the peri-implantation window,¹⁸ and analogous profiles have been described in older endometria without overt pathology.

Decidualization Failure and Progesterone Signaling

Decidualization is impaired with age: aged stromal cells show reduced expression of decidualization markers (prolactin, IGFBP-1), attenuated morphological transformation, and diminished capacity to mount the controlled pro-inflammatory response required for embryo invasion. Wang and colleagues demonstrated that aged endometrium loses histone H3 lysine 27 acetylation at progesterone-receptor target genes, with consequent downregulation of progesterone-receptor expression and impaired decidual response.¹⁹ An influential conceptual advance is the recognition that the decidualized endometrium functions as a biosensor of embryo quality: Teklenburg, Brosens, Macklon and colleagues demonstrated that decidualized stromal cells differentially modulate their cytokine secretion in response to competent versus chromosomally abnormal embryos.^20–22 Aged endometrium with its decidualization defects may lose some of this discriminatory capacity, contributing to higher early pregnancy loss observed in older women.

Transcriptomic Remodeling, Epigenetic Drift, and Extracellular Vesicles

Genome-wide transcriptomic analysis of the endometrium of women over 35 years identified 5,778 dysregulated genes, with ciliary processes as the primary dysregulated function, together with altered expression of genes required for receptivity (PAEP, MMP26), cell-cycle arrest (FGF2), telomere maintenance (TINF2) and genomic stability (SIRT1).²³ Loid and colleagues described an age-related expansion of multi-ciliated epithelial cells together with miR-34/449-mediated dysregulation that may interfere with trophoblast invasion.²⁴ Beyond histone modifications, DNA-methylation-based epigenetic clocks indicate that the endometrium ages epigenetically, and the age-related dysregulation of telomere-maintenance and genomic-stability genes described above suggests a broader epigenetic drift in the aging endometrium.²⁵ Extracellular vesicles (EVs) secreted by endometrial cells participate in nearly every step of implantation, and aging may alter EV secretion, cargo composition, and uptake efficiency, representing a substantially under-investigated dimension of endometrial aging.²⁶

Vascular Decline, Structural Changes, and Immune Dysregulation

With age, endometrial microvascular density declines, spiral artery remodeling becomes less efficient, and stromal fibrosis increases, contributing to higher rates of pregnancy loss, placental insufficiency, and hypertensive disorders in older mothers.²⁷ A systematic review of age-related uterine changes documented progressive loss of spiral arteriole volume from age 35, mineral deposition in uterine arteries, and a thinner endometrium in women over 35–40 years, changes that reinforce the importance of careful uterine evaluation prior to embryo transfer.²⁵ The maternal immune compartment shifts in parallel with systemic immunosenescence: uterine natural killer cell numbers and functional activity decline, regulatory T cell function is attenuated, and the pro-inflammatory/tolerogenic balance tilts toward inflammation, increasing the risk of immune-mediated implantation failure and the elevated preeclampsia rates observed in donor-oocyte pregnancies.²⁸

CLINICAL EVIDENCE OF ENDOMETRIAL AGING

Pregnancy and Live Birth in Donor-Oocyte Cycles

Donor-oocyte cycles isolate the endometrial contribution to reproductive outcome by holding oocyte quality constant. Yeh and colleagues, analyzing more than 27,000 first-fresh-donor cycles from the SART registry, demonstrated a graded decline in live birth rate with increasing recipient age.¹¹ Williams and colleagues confirmed this trend in a SART registry analysis of 40,485 donor-oocyte cycles from 2016–2018, in which the odds of live birth after single embryo transfer fell progressively with recipient age (OR 0.80 at 40–44 years, 0.77 at 45–49 years and 0.65 above 49 years).¹² The Sebastian-Leon cohort represents the most granular analysis to date, documenting a live birth rate decline from 45.8% at age 40 to 32.7% at age 50, with significant annual increases in implantation failure (4.2% per year) and pregnancy loss (3.2% per year) beyond age 40.¹³ Three principles emerge from this literature: the endometrium contributes independently to outcome; the contribution is graded across age; and absolute outcomes remain clinically meaningful into the fifth decade. (Table 3)

Implantation Failure and Pregnancy Loss with Euploid Embryos

Even after transfer of a single euploid blastocyst, live birth declines progressively with maternal age. Reig and colleagues, analyzing 8,175 single euploid embryo transfers, found that implantation rates were negatively correlated with age: after adjustment for confounders, women aged 38 years or older had significantly lower implantation rates than those under 35 (OR 0.85 for 38–40 years, 0.69 for 41–42 years and 0.69 for >42 years), with parallel differences in clinical pregnancy and live birth rates, whereas the rates of progression from implantation to clinical pregnancy and from clinical pregnancy to live birth did not differ significantly by age group.²⁹ Consistently, a systematic review and meta-analysis of 11,335 euploid embryo transfers, together with an analysis of PGT-A cycles recorded in the SART registry, documented a progressive decline in cumulative live birth per euploid transfer from 54.8% in women under 35 to 46.2% in women over 42 years, a difference of nearly nine percentage points that cannot be attributed to aneuploidy.³⁰ These findings support endometrial aging as an independent factor operating beyond oocyte aneuploidy. Endometrial preparation may also matter: Rafael and colleagues, in a multicentre cohort of 67,048 donor-oocyte single blastocyst transfers, found that natural cycles were associated with a higher live birth rate (adjusted OR 1.38) and a lower miscarriage rate (adjusted OR 0.68) than artificial cycles, and that this advantage was not modified by recipient age (non-significant interaction), suggesting that the preparation protocol is a modifiable factor to be considered alongside recipient age.³¹ Together, these findings underscore the need for age-stratified, protocol-controlled prospective studies.

Diagnostic Tools and Endometrial Biomarkers

Identifying the aging endometrium in clinical practice has historically relied on endometrial thickness and morphological pattern, which correlate only loosely with implantation success. In a systematic review of 142 studies with meta-analysis, Marti-Garcia and colleagues found that women over 35–40 years have a thinner endometrium (mean difference 0.52 mm) and, in donor-oocyte cycles, lower odds of implantation (OR 0.73) and clinical pregnancy (OR 0.80) and higher odds of pregnancy loss (OR 1.44), while no validated biomarker of biological endometrial age is yet available,²⁵ Candidate markers under investigation include p16-positive senescent cells and multiciliated cell accumulation, DNA-methylation (epigenetic clock) estimates of endometrial age, and transcriptomic aging signatures, but these have not been combined into a clinically validated panel for stratifying women by biological rather than chronological age.

Obstetric and Perinatal Outcomes

Even when pregnancy is achieved, older mothers face increased risks of hypertensive disorders, gestational diabetes, placental insufficiency, intrauterine growth restriction, preterm birth, and stillbirth.^27,32,33 Donor-oocyte pregnancies show particularly elevated rates of preeclampsia, attributed to immunological mismatch and age-related vascular and decidual dysfunction.²⁸ The magnitude increases markedly after age 40 and again after age 45, though absolute risk remains acceptable in carefully monitored patients.

PREGNANCY AT ADVANCED MATERNAL AGE: THE REAL NUMBERS AND THE PUBLIC NARRATIVE

The social and media landscape surrounding reproduction at advanced maternal age has undergone a marked transformation. Widely publicized pregnancies and births among public figures in their late forties and fifties rarely specify the underlying reproductive strategy, yet they undeniably influence how women perceive their own reproductive options. A central message for clinical counseling is that although reproductive outcomes decline progressively with age, they are not zero. In donor-oocyte cycles, live birth rates remain above 30% per transfer at age 50.¹³ The accurate framing is not “it is impossible” but “the odds decrease and the risks rise, but a successful pregnancy remains a realistic goal for many women.”

The celebrity visibility of late motherhood has the unintended consequence of underrepresenting the role of egg donation and gestational surrogacy. Transparent counseling that addresses all available options: own oocytes, frozen oocytes from earlier years, donor oocytes, donor embryos, and gestational surrogacy where legally available supports informed decision-making aligned with individual values and goals.

EMERGING THERAPEUTIC STRATEGIES

No single therapeutic target addresses the multifactorial nature of endometrial aging; strategies addressing multiple mechanisms or upstream regulatory nodes are therefore likely to be most clinically effective. The proposed therapies are summarized in Table 4.

Senolytics and Senomorphics

Pharmacological elimination of senescent cells (senolytics, such as dasatinib plus quercetin) and inhibition of the SASP (senomorphics) are under active investigation for age-related diseases.³⁶ In endometrial models, senolytic strategies have restored decidualization and reduced inflammatory cytokine release.²⁶ Clinical translation to reproductive medicine remains preclinical, and safety in the reproductive context requires careful evaluation before clinical adoption.

Epigenetic and Hormonal Modulators

Strategies aimed at restoring progesterone-receptor signaling, including epigenetic modifiers targeting H3K27 acetylation, have shown promise in preclinical models.¹⁹ Sonic Hedgehog pathway agonists may rejuvenate endometrial mesenchymal stem cells. Whether tailored estrogen-progesterone regimens can compensate for the diminished progesterone responsiveness of aged endometrium remains an open question.

Stem Cell-Based Approaches

Autologous endometrial stem cell therapies, including intrauterine instillation of bone marrow-derived mesenchymal stem cells, have been studied in small series of women with refractory thin endometrium and Asherman syndrome. Application specifically to age-related endometrial decline remains exploratory.

Platelet-Rich Plasma: The Most Clinically Advanced Option

Autologous platelet-rich plasma (PRP) is a centrifuged platelet concentrate releasing growth factors (PDGF, TGF-β, VEGF, EGF, IGF, bFGF) that target the vascular, proliferative, and anti-inflammatory deficits characteristic of the aged endometrium.^37–39 A 2024 meta-analysis of eight randomized controlled trials including 678 patients reported that intrauterine PRP significantly increased endometrial thickness (mean difference 1.23 mm), clinical pregnancy rate (RR 2.04), live birth rate (RR 2.46), and implantation rate (RR 2.71), without significant adverse events.³⁴ Lad and colleagues demonstrated improved endometrial thickness specifically in older women who had failed conventional hormone replacement therapy.³⁵ An important limitation is that not all PRP preparations are equivalent: biological potency depends critically on platelet concentration, preparation method, and activation protocol.^40,41 Because none of these is standardized, quality and effectiveness vary widely between centers, making broadly applicable recommendations premature. Additional limitations include absence of RCTs specifically targeting chronological endometrial aging. The 2024 Cochrane review, which included 12 randomized controlled trials (1,069 women), rated the certainty of evidence as very low for almost all outcomes, including live birth and clinical pregnancy, and found no significant benefit of intrauterine PRP when the analysis was restricted to trials at low risk of bias.⁴²

Extracellular Vesicles and Exosomes

Extracellular vesicles (EVs), particularly exosomes, small membrane-bound vesicles of endosomal origin — have emerged as potent mediators of intercellular communication at the embryo-endometrial interface. Endometrial-derived exosomes carry a cargo of proteins, lipids, and regulatory RNAs that modulate trophoblast adhesion, invasion, and immune tolerance.^43–45 In the aging uterus, mesenchymal stem cell-derived exosomes promote angiogenesis, exert anti-fibrotic effects by suppressing TGF-β-mediated myofibroblast differentiation, support endometrial proliferation and regeneration, and modulate immune responses by expanding regulatory T cells mechanisms directly relevant to the aged endometrium. Acting simultaneously on angiogenesis, anti-fibrosis, remodeling, proliferation, and immunomodulation, EV-based therapies may eventually represent one of the most mechanistically precise interventions for the aging uterus. No clinical data yet exist for age-related endometrial decline specifically, but the biological rationale is strong.^43–45

DISCUSSION

Endometrial aging reflects the cumulative impact of cellular senescence, epigenetic drift, vascular decline, and immune dysregulation, creating a uterine environment less supportive of implantation even with euploid embryos. Clinically, implantation and live birth rates decline with advancing age, including in donor-oocyte cycles confirming the endometrium as an independent determinant of reproductive outcomes.^13,17 Emerging therapies, including senolytics, epigenetic modulation, and regenerative approaches such as PRP, aim to restore endometrial function.

Despite the rapid growth of the endometrial-aging literature, several methodological limitations should be acknowledged. Women of advanced reproductive age represent a self-selected population; most studies are retrospective; transcriptomic analyses are limited by small samples and cross-sectional designs; the biosensor function has not been systematically investigated across age strata; and the therapeutic literature suffers from substantial heterogeneity. The gestational surrogacy literature is particularly sparse with respect to gestational carrier age differences, and dedicated prospective studies in this population are a priority.

One area that merits explicit discussion is the comparison of reproductive outcomes between proven gestational carriers of different ages. Although gestational surrogacy represents a growing reproductive pathway including for older family members willing to carry pregnancies for relatives the literature on how gestational carrier age affects outcomes remains unfortunately limited. Current evidence is insufficient to establish age-specific thresholds for gestational carriers based on endometrial biology alone, and this gap represents an important unresolved clinical question.

FUTURE DIRECTIONS

Several priority areas emerge from this review. First, age-stratified prospective studies with standardized endometrial endpoints are needed to characterize the contribution of chronological versus biological endometrial age to reproductive outcome. Second, dedicated randomized trials of regenerative therapies: PRP, senolytics, and epigenetic modulators should be conducted in age-defined populations rather than extrapolated from thin-endometrium or recurrent-implantation-failure cohorts.

Third, and of particular emerging importance, artificial intelligence (AI) represents a promising tool for the identification and classification of the aging endometrium.⁴⁶ Machine-learning and deep-learning models applied to endometrial imaging, histological, and molecular data may enable automated, reproducible, and non-invasive estimation of biological endometrial age with greater precision than any single biomarker.

Fourth, the role of gestational carrier age in surrogacy outcomes warrants dedicated investigation. As surrogacy becomes more common; including intrafamilial arrangements where mothers, grandmothers, and other older relatives serve as gestational carriers, the question of how carrier age affects endometrial receptivity and pregnancy outcomes becomes clinically urgent. A particularly valuable research design would be to compare outcomes in gestational carrier cycles stratified by carrier age among proven carriers; women who have demonstrated prior successful pregnancies thereby isolating the effect of chronological endometrial aging from confounding variables such as nulliparity or unknown reproductive history. Unfortunately, the current literature is very limited in age differences among gestational carriers, and prospective registries capturing carrier age, endometrial biological markers, and pregnancy outcomes are needed to fill this gap.

Fifth, validated biomarker panels integrating p16 expression, telomere length, epigenetic clock data, and transcriptomic age estimators should be prospectively validated against clinical outcomes in independent cohorts, with clear clinical decision thresholds established for use in reproductive medicine practice.

CONCLUSION

The longstanding view that the uterus does not age is no longer tenable. Convergent clinical, transcriptomic, mechanistic, and epigenetic evidence demonstrates that endometrial aging is an independent biological process that contributes to implantation failure, pregnancy loss, and reduced live birth rates in women of advanced reproductive age. Recognizing endometrial aging as a distinct therapeutic target represents an important frontier in contemporary reproductive medicine.

Reproductive outcomes decline with age, but they are not zero. Among emerging therapies, intrauterine platelet-rich plasma is currently the most clinically advanced option, although dedicated trials in age-defined populations are still required. Future progress will depend on integrating molecular profiling; including AI-based tools for endometrial classification, regenerative interventions, and individualized counseling into the reproductive care of women across the entire reproductive lifespan, recognizing that the endometrium is not a passive vessel but an actively aging, biologically informative, and therapeutically actionable organ.

Authors’ Contribution - CRediT

Conceptualization: Tamar Alkon (Equal), Ricardo H. Asch Schuff (Equal). Investigation: Tamar Alkon (Equal), Jorge Suarez (Equal), Ricardo H. Asch Schuff (Equal). Writing – original draft: Tamar Alkon (Equal), Jorge Suarez (Equal), Ricardo H. Asch Schuff (Equal). Writing – review & editing: Tamar Alkon (Equal), Jorge Suarez (Equal), Ricardo H. Asch Schuff (Equal). Supervision: Ricardo H. Asch Schuff (Lead).