A Review of Mechanisms of Implantation

Tire rubber-derived contaminants 6PPD and 6PPD-quinone reduce attachment and outgrowth of trophoblast spheroids onto endometrial epithelial cells

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a synthetic additive widely used in the rubber industry, and its oxidized product 6PPD-quinone (6PPDQ), have garnered widespread attention as an emerging hazardous chemicals owing to their potential detrimental effects on aquatic ecosystem and human health. The effects of 6PPD and 6PPDq on the female reproductive tract, especially embryo implantation, remain unknown and were investigated in this study. We used the spheroid attachment and outgrowth models of BeWo trophoblastic spheroids and Ishikawa cells as surrogates for the human blastocyst and endometrial epithelium, respectively. Treatment with the chemicals for up to 48 h decreased the viability of the cells in a dose- and cell line-dependent manner (20-100 μM 6PPD and 10-100 μM 6PPDQ for both the cell lines). At a noncytotoxic concentration, exposure of Ishikawa cells to 1 and 10 μM 6PPD reduced the attachment of BeWo spheroids and further inhibited their invasion and outgrowth on the endometrial epithelial monolayer. A similar result was observed in 1 μM 6PPDQ-exposed groups. Gene expression profiling of 6PPD- and 6PPDQ-exposed endometrial epithelial cells revealed that both 6PPD and 6PPDQ differentially regulated a panel of transcript markers toward overall downregulation of receptivity and invasion. The study provides the first proof of the adverse effects of 6PPD and 6PPDQ on human endometrial receptivity and trophoblast invasion during the window of implantation, warranting the need for further in vivo and clinical studies.

Tri-o-tolyl phosphate impedes implantation: Malfunction of mitochondria and disruption of calcium homeostasis through MAPK and AKT signaling cascades

Tri-o-tolyl phosphate (TOTP), a flame retardant containing aryl compounds, is widely used in human living environments owing to its several applications. However, Due to the overuse of TOTP, its residue has been identified in various environments and non-targeted organisms, including humans. Although extensive research is being conducted to address the toxicity of this substance, its potential reproductive toxicity in females has not been sufficiently studied. In this study, human HTR-8/SVneo and JEG-3 trophoblasts were used to investigate the effects of TOTP on implantation. Results showed that TOTP decreased cell viability and inhibited cell proliferation by triggering cell cycle arrest. It also induced apoptosis and mitochondrial dysfunction, disrupted calcium homeostasis, increased the influx of calcium ions into the mitochondria, and disturbed cell aggregation and migration. Moreover, the MAPK and AKT cell signaling pathways were altered, and crosstalk between these pathways were distinguished. Thus, inhibitors of the MAPK and AKT pathways exhibited potential for managing the toxicity of TOTP. Overall, this study demonstrated the reproductive toxicity of TOTP in human females and elucidated the underlying mechanisms. Our results highlighted the potential risks associated with TOTP.

Dead or Alive: Exploratory Analysis of Selected Apoptosis- and Autophagy-Related Proteins in Human Endometrial Stromal Cells of Fertile Females and Their Potential Role During Embryo Implantation

To date, very little is known about how apoptosis and autophagy affect human endometrial stromal cells (ESCs), particularly how these processes might determine the depth of implantation in humans. Before investigating how apoptosis and autophagy might modulate the implantation process in an infertile population, it is necessary to clarify how these processes are regulated in healthy individuals. This study examined the protein expression related to apoptosis and autophagy in primary ESCs from fertile women, particularly in the context of decidualization and embryo contact, using Western blot analysis. This study evaluated the protein expression of apoptosis receptors and autophagy markers during the window of implantation. Previous research has shown that a syndecan 1 (Sdc1) knockdown (kd) in endometrial stromal cell lines increased the sensitivity to apoptosis induced by embryonic stimuli. We aimed to determine if this effect is also present in primary cells and if Sdc1 regulates autophagy. The expression of autophagy- and apoptosis-associated proteins in primary ESCs from fertile individuals was investigated in this preliminary study, along with their impact on the process of human embryo implantation. During decidualization and exposure to embryo contact, we observed an upregulation of apoptosis- and autophagy-related proteins in ESCs. Decidualized ESCs exhibited higher levels of apoptosis receptors, indicating increased sensitivity to embryo-induced apoptosis. Additionally, the increase in basal autophagy proteins suggests a significant role in the implantation process. Sdc1 is potentially involved in regulating apoptosis and autophagy, demonstrating its possible role in modulating implantation-related cell activities. These findings suggest a complex interplay between apoptosis and autophagy in regulating human embryo implantation. The changes in the expression of apoptotic and autophagic proteins in ESCs after decidualization and upon contact with the embryo provide new insights into the cellular mechanisms that underlie successful implantation. These results have potential implications for understanding the pathophysiology of implantation disorders and improving assisted reproductive technologies. The first results of this pilot study need to be verified with a larger sample size in the future.

A pilot study of transcriptomic preimplantation genetic testing (PGT-T): towards a new step in embryo selection?

STUDY QUESTION

Is it possible to predict an euploid chromosomal constitution and identify a transcriptomic profile compatible with extended embryonic development from RNA sequencing (RNA-Seq) data?

SUMMARY ANSWER

It has been possible to obtain a karyotype comparable to preimplantation genetic testing for aneuploidy (PGT-A), in addition to a transcriptomic signature of embryos which might be suggestive of improved implantation capacity.

WHAT IS KNOWN ALREADY

Conventional assessment of embryo competence, based on morphology and morphokinetic, lacks knowledge of molecular aspects and faces controversy in predicting ploidy status. Understanding the embryonic transcriptome is crucial, as gene expression influences development and implantation. PGT has improved pregnancy rates, but problems persist when high-quality euploid embryos do not reach term. In fact, only around 50-60% implant, of which 10% result in miscarriage. Comprehensive approaches, including RNA-Seq, offer the potential to discover molecular markers of reproductive competence, and could theoretically be combined with extended-embryo culture platforms up to Day 14 that can be utilized as a proxy to study embryo development at post-implantation stages.

STUDY DESIGN, SIZE, DURATION

This prospective pilot cohort study was conducted from March 2023 to August 2023. A total of 30 vitrified human blastocysts with previous PGT-A diagnosis on Day 5 (D5) or Day 6 (D6) of development were analysed: n = 15 euploid and n = 15 aneuploid. Finally, 21 embryo samples were included in the study; the rest (n = 9) were excluded due to poor quality pre-sequencing data (n = 7) or highly discordant data (n = 2).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Following warming and re-expansion, embryos underwent a second trophectoderm (TE) biopsy. The embryos were then cultured until day 11 to assess their development. Biopsy analysis by RNA-Seq, studied the differential expressed genes (DEG) to compare embryos which did not or did attach to the plate: unattached embryos (n = 12) versus attached embryos (n = 9). Thus, we also obtained a specific transcriptomic signature of embryos with a "theoretical" capacity for sustained implantation, based on plate attachment on day 11.

MAIN RESULTS AND THE ROLE OF CHANCE

The digital karyotype obtained by RNA-Seq showed good concordance with the earlier PGT-A data, with a sensitivity of 0.81, a specificity of 0.83, a Cohen's Kappa of 0.66, and an area under the ROC of 0.9. At the gene level, 76 statistically significant DEGs were found in the comparison unattached versus attached embryos (Padj < 0.05; FC > 1). To address the functional implications of these differences, significantly deregulated pathways according to GO and KEGG categories were identified. The mural trophectoderm (TE) of the unattached blastocysts showed 63 significantly deregulated terms, displaying upregulation in autophagy, apoptosis, protein kinase and ubiquitin-like protein ligase activity, and downregulation of ribosome, spliceosome, kinetochore, segregation, and chromosome condensation processes. The overall transcriptomic signature specific to embryos still attached to the plate on day 11 (with a theoretically higher implantation capacity) consists of 501 genes, including: EMP2, AURKB, FOLR1, NOTCH3, LRP2, FZD5, MDH1, APOD, GPX8, COLEC12, HSPA1A, CMTM7, BEX3, which are related to implantation and embryonic development (raw P-value < 0.05; shrunk LFC > 1.1). These findings indicate that it might be possible to identify euploid embryos with a greater capacity for implantation and development, after excluding those embryos that present chromosomal alterations.

LIMITATIONS, REASONS FOR CAUTION

This study included a small sample size, remarkable variability between samples, and low success rate of RNA amplification. Also, structural chromosomal abnormalities were not included, and it was not possible to diagnose mosaic embryos. TE biopsy does not assure the chromosomal status of the whole embryo. The maximum day for in vitro development was Day 11, and attachment to the plate on this day does not provide a clear indication of implantation capacity and viability, which was not tested in this study.

WIDER IMPLICATIONS OF THE FINDINGS

The short-term goals following on from this pilot study is to expand the sample size with embryos of more complex abnormalities, and to perform a prospective in vitro preclinical validation. In a more distant future and with optimal results, this technique could have clinical application, thus increasing clinical outcomes by assessing both chromosomal content and transcriptomic profiling.

STUDY FUNDING/COMPETING INTEREST(S)

The Institut Valencià de Competitivitat Empresarial (IVACE) (IMIDCA/2022/39) and Generalitat Valenciana (CIACIF/2021/11) supported the present study. A.C. is an employee of JUNO Genetics. He has received honoraria for an IBSA lecture and a Merck lecture. He is also a minor shareholder of IVIRMA Global. The other authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

The Interplay of Molecular Factors and Morphology in Human Placental Development and Implantation

The placenta is a vital organ that supports fetal development by mediating nutrient and gas exchange, regulating immune tolerance, and maintaining hormonal balance. Its formation and function are tightly linked to the processes of embryo implantation and the establishment of a robust placental-uterine interface. Recent advances in molecular biology and histopathology have shed light on the key regulatory factors governing these processes, including trophoblast invasion, spiral artery remodeling, and the development of chorionic villi. This review integrates morphological and molecular perspectives on placental development, emphasizing the roles of cytokines, growth factors, and signaling pathways, such as VEGF and Notch signaling, in orchestrating implantation and placental formation. The intricate interplay between molecular regulation and morphological adaptations highlights the placenta's critical role as a dynamic interface in pregnancy. This review synthesizes current findings to offer clinicians and researchers a comprehensive understanding of the placenta's role in implantation, emphasizing its importance in maternal-fetal medicine. By integrating these insights, the review lays the groundwork for advancing diagnostic and therapeutic approaches that can enhance pregnancy outcomes and address related complications effectively.

A stress paradox: the dual role of the unfolded protein response in the placenta

The placenta is a temporary organ that forms during pregnancy and is essential for fetal development and maternal health. As an endocrine organ, proper placental function requires continual production, folding, and transport of proteins and lipids. Central to these processes is the endoplasmic reticulum (ER), a dynamic organelle responsible for maintaining cellular protein and lipid synthesis and processing. ER stress occurs when there is an accumulation of unfolded or misfolded proteins, which triggers the activation of cellular pathways collectively called the unfolded protein response. Unfolded protein response pathways act to alleviate the misfolded protein burden and restore ER homeostasis, or if unresolved, initiate cell death. While prolonged ER stress has been linked to deficient placental function and adverse pregnancy outcomes, basal activation of unfolded protein response pathways is required for placental development and function. This review explores the importance of ER homeostasis in placental development and function, examining how disruptions in ER stress responses may contribute to adverse pregnancy outcomes.

Transcriptomic alterations in the ovine caruncular endometrium due to imbalanced nutrition and FSH-induced ovarian hyperstimulation

BACKGROUND

Imbalanced diet and exogenous gonadotrophins affect uterine function and morphology. In sheep, FSH-induced superovulation alters implantation-related gene expression, influenced by both treatment and diet. In this study, we used deep RNA sequencing (NGS, RNA-Seq) to expand our understanding of these effects on the caruncular endometrium.

METHODS

Ewes (n = 3-5/group) were separated into control fed (CF), overfed (OF), and underfed (UF) groups, with each group subdivided between FSH (superovulated; SOV) or saline (negative controls; CONT) treatment. Caruncular samples were collected on day 10 of diestrus of the subsequent estrous cycle, with samples from CF_CONT also collected on day 5 to assess time-dependent changes.

RESULTS

The 1484 differentially expressed genes (DEGs, P < 0.01, FDR < 0.05) identified between CF_CONT animals at days 5 and 10 were predominantly associated with increased immune activity and cellular metabolic processes and cellular proliferation. In CONT animals, imbalanced nutrition (i.e., both OF and UF) was associated with enrichment of terms associated with cell adhesion and differentiation, immune response and angiogenesis. The FSH carry-over effects resulted in a higher number of DEGs in CF animals (1374), than in OF (168) or UF (18), mostly associated with dysregulation of cell cycle and hormonal sensitivity.

CONCLUSION

The absence of genes concurrently affected by superovulation (SOV) in all feeding regimes indicates that the effects of FSH on the caruncular transcriptome are multidirectional and dependent upon body condition. Therefore, the homeostasis of ovine caruncles is influenced by both body condition and superovulation (SOV), potentially affecting uterine receptivity.

MicroRNAs as Biomarkers and Therapeutic Targets in Female Infertility

The study of microRNAs (miRNAs) has emerged in recent decades as a key approach to understanding the pathophysiology of many diseases, exploring their potential role as biomarkers, and testing their use as future treatments. Not only have neurological, cardiovascular diseases, or cancer benefited from this research but also infertility. Female infertility, as a disease, involves alterations at multiple levels, such as ovarian and uterine alterations. This review compiles the latest studies published in humans that link female disorders that affect fertility with altered miRNA profiles. Studies on ovarian alterations, including diminished ovarian reserve (DOR), poor ovarian response to stimulation (POR), premature ovarian insufficiency (POI), and polycystic ovary syndrome (PCOS), are summarized and classified based on the expression and type of sample analyzed. Regarding uterine disorders, this review highlights upregulated and downregulated miRNAs primarily identified as biomarkers for endometriosis, adenomyosis, decreased endometrial receptivity, and implantation failure. However, despite the large number of studies in this field, the same limitations that reduce reproducibility are often observed. Therefore, at the end of this review, the main limitations of this type of study are described, as well as specific precautions or safety measures that should be considered when handling miRNAs.

Resmethrin induces implantation failure by disrupting calcium homeostasis and forcing mitochondrial defects in porcine trophectoderm and uterine luminal epithelial cells

Resmethrin, a type I pyrethroid insecticide, is frequently used globally in residential and farmland areas to control pests. Owing to the repeated administration of resmethrin, and particularly because of its lipophilic nature, residues have been detected in various environments, crops, and livestock. Previous studies have shown the adverse effects of resmethrin, including neurotoxicity and hepatotoxicity. However, the toxic effects of resmethrin on the female reproductive system have rarely been investigated. In the present study, we used two cell types, porcine trophectoderm (pTr) and porcine uterine luminal epithelial (pLE) cells, to examine the toxic effects of resmethrin on implantation and its mechanisms. Our study showed that resmethrin exposure induced apoptosis and inhibited cell cycle progression, thereby reducing the viability of both cell types. In addition, calcium homeostasis was disrupted following resmethrin treatment, and disrupted calcium homeostasis impaired the mitochondrial membrane potential and mitochondrial respiration. In addition to mitochondrial dysfunction, GRP75 and ER stress-related proteins were upregulated. Furthermore, the AKT and MAPK cascades were altered, and reactive oxygen species production and inflammation occurred after resmethrin treatment. Ultimately, through various mechanisms, resmethrin decreased the migratory abilities, and it could diminish the crosstalk between the two cell lines and lower the probability of successful implantation. Overall, we demonstrated that resmethrin interfered with the implantation process by triggering various toxic mechanisms. This study presents, for the first time, evidence regarding the mechanisms through which resmethrin exerts toxic effects on the female reproductive system, thereby raising awareness regarding the potential implications of its widespread use.

Investigating the Imperative Role of microRNAs Expression in Human Embryo Implantation: A Narrative Review Based on Recent Evidence

BACKGROUND/OBJECTIVES

Embryo implantation is a highly complex process that requires the precise regulation of numerous molecules to be orchestrated successfully. Micro RNAs (miRNAs) are small non-coding RNAs that regulate gene expression and play a crucial role in the regulation of embryo implantation. This article aims to summarize the key findings of the literature regarding the role of miRNAs in human embryo implantation, emphasizing their involvement in critical stages such as decidualization, endometrial receptivity and trophoblast adhesion.

METHODS

This review includes primary research articles from the past decade. The studies utilize a range of experimental methodologies, including gene expression analysis and in vitro studies.

RESULTS

MicroRNAs, like miR-320a, miR-149, and miR30d secreted by preimplantation embryos and blastocysts significantly influence endometrial receptivity by promoting essential cellular processes, such as cell migration and trophoblast cell attachment, while others-miR17-5p, miR-193-3p, miR-372, and miR-542-3p-secreted from the endometrium regulate the decidualization phase. During the apposition and adhesion phases, miRNAs play a complex role by promoting, for example, miR-23b-3p, and inhibiting-as do miR-29c and miR-519d-3p-important biological pathways of these stages. During invasion, miR-26a-5p and miR-125-5p modulate important genes.

CONCLUSIONS

This review underscores the critical impact of miRNAs in the regulation of embryo implantation and early pregnancy. The ability of miRNAs to modulate gene expression at various stages of reproduction presents promising therapeutic avenues for improving assisted reproductive technologies outcomes and addressing infertility. Further research into miRNA-based diagnostic tools and therapeutic strategies is essential to enhance our understanding of their role in reproductive health and to exploit their potential for clinical applications.

Fatty Acid Metabolism Disruptions: A Subtle yet Critical Factor in Adverse Pregnancy Outcomes

The establishment and maintenance of pregnancy encompass a series of complex and high-energy-consuming physiological processes, resulting in a significant energy demand. Fatty acids, one of the most essential nutrients, play a crucial role in energy supply via oxidation and perform critical biological functions such as anti-inflammatory and anti-oxidant effects, which substantially impact human health. Disordered fatty acid metabolism can cause anomalies in fetal growth and development, as well as a range of pregnancy problems, which can influence the health of both the mother and the fetus. In this review, we innovatively explore the relationship between fatty acid metabolism abnormalities and pregnancy complications, emphasizing the potential of dietary interventions with polyunsaturated fatty acids in improving pregnancy outcomes. These findings provide important evidence for clinical interventions and enhance the understanding and practical application of health management during pregnancy.

Pregnancy rate and time to pregnancy after recurrent implantation failure (RIF)-a prospective cohort follow-up study

PURPOSE

The goal of this study was to determine ongoing pregnancy rate, time to pregnancy and embryo transfers to pregnancy within a cohort of patients with recurrent implantation failure (RIF).

METHODS

IVF patients with RIF were included after referral to the RIF outpatient clinic. They received a questionnaire 1 year after inclusion. If data was missing, medical files were examined to determine pregnancy outcomes and conception methods. The ability of the RIF outpatient clinic to improve pregnancy chance or increase the number of patients who elected to continue treatment was beyond the scope of this study.

RESULTS

The cumulative incidence of ongoing pregnancy in IVF patients with RIF (n = 79) after 1 year of follow-up was 40.5% (95% confidence interval = 30.4-51.5%). Median time to pregnancy was 4 months. Pregnancy incidence increased gradually up to 5 embryo transfers (mostly single embryo transfers). The average embryo transfers to pregnancy were 7.3 transfers.

CONCLUSION

In IVF patients with RIF, up until the 5th embryo transfer, each transfer represents a good opportunity for ongoing pregnancy. This data can be used to counsel patients that regular treatment continuation seems to be well justified even when IVF patients fulfil the RIF criteria.

TRIAL REGISTRATION

CCMO: NL66835.068.18. METC 18-040. OMON: NL-OMON24778.

Rapid increase of MFGE8 secretion from endometrial epithelial cells is an indicator of extracellular vesicle mediated embryo maternal dialogue

Successful embryo implantation relies on synchronized dialog between the embryo and endometrium, and the role of extracellular vesicles (EVs) in facilitating this cross-talk has been recently established. In our previous study, milk fat globule-EGF factor 8 protein (MFGE8) was identified as increasing in receptive endometrial epithelial cells (EECs) in response to trophoblastic EVs. However, the dynamics of MFGE8 protein in this context are not completely understood. Therefore, we examined its expression and secretion in EECs exposed to estrogen, progesterone, and trophoblastic EVs to gain deeper insights into its potential as an indicator of EV-mediated embryo-maternal dialogue. Our findings revealed that MFGE8 secretion is sensitive to estrogen and progesterone, and that trophoblastic EVs stimulate their release in both receptive and non-receptive EECs. Furthermore, trophoblast EV function was dose and time-dependent. Notably, the secretion of MFGE8 increased within a short timeframe of 30 min after addition of EVs, suggesting the possibility of rapid processes such as binding, fusion or internalization of trophoblastic EVs within EECs. Interestingly, MFGE8 released from EECs was associated with EVs, suggesting increased EV secretion from EECs in response to embryonic signals. In conclusion, increased MFGE8 secretion in this embryo implantation model can serve as an indicator of EV-mediated embryo-maternal dialogue.

Exploring the black box of human reproduction: endometrial organoids and assembloids - generation, implantation modeling, and future clinical perspectives

One of the critical processes in human reproduction that is still poorly understood is implantation. The implantation of an early human embryo is considered a significant limitation of successful pregnancy. Therefore, researchers are trying to develop an ideal model of endometrium in vitro that can mimic the endometrial micro-environment in vivo as much as possible. The ultimate goal of endometrial modeling is to study the molecular interactions at the embryo-maternal interface and to use this model as an in vitro diagnostic tool for infertility. Significant progress has been made over the years in generating such models. The first experiments of endometrial modeling involved animal models, which are undoubtedly valuable, but at the same time, their dissimilarities with human tissue represent a significant obstacle to further research. This fact led researchers to develop basic monolayer coculture systems using uterine cells obtained from biopsies and, later on, complex and multilayer coculture models. With successful tissue engineering methods and various cultivation systems, it is possible to form endometrial two-dimensional (2D) models to three-dimensional (3D) organoids and novel assembloids that can recapitulate many aspects of endometrial tissue architecture and cell composition. These organoids have already helped to provide new insight into the embryo-endometrium interplay. The main aim of this paper is a comprehensive review of past and current approaches to endometrial model generation, their feasibility, and potential clinical application for infertility treatment.

APOE-E4 allele as a potential marker for implantation failure: A comparison between fertile women, ART success and RIF patients

OBJECTIVE

Apolipoprotein E (APOE) is the most important precursor for the production of steroid hormones and is also involved in regulating the function of steroid hormones, hence playing a significant role in reproductive processes. So, APOE gene expression may be correlated with the implantation process. This study tries to make a better clarification of the correlation between APOE gene polymorphisms and recurrent implantation failure (RIF), where we compared the frequency of APOE polymorphisms in RIF patients, assisted reproductive treatment (ART) success cases and fertile women.

METHOD

In all, 100 women with successful ART who got pregnant (fetal heart rate positive) in their first or second cycle of in vitro fertilization or intracytoplasmic sperm injection, 100 infertile RIF cases, and 100 normal fertile control cases with at least one live birth were included in present study. Following DNA extraction, genotypes were determined through polymerase chain reaction-restriction fragment length polymorphism method using HhaI restriction enzyme. Finally, statistical analysis was performed by chi-squared (χ2) test in SPSS software (P < 0.05).

RESULTS

The RIF group showed significantly higher frequency for E3/E4 genotype (29%) compared with the other two control groups (fertile = 15%, ART success [ART+] = 13%) (P = 0.007). There was also a significantly higher frequency of the E4 allele in the RIF group (14.5%) compared with both of the control groups (fertile = 7.5%, ART+ = 6.5%) (P = 0.018).

CONCLUSION

APOE4 is correlated with recurrent failure in the process of embryo implantation and, accordingly, it may potentially be considered a possible risk factor to the implantation process. The presence of E4 can be proposed as a predictive indicator in determining the results of assisted reproductive techniques.

Emerging Roles of IL-27 in Trophoblast Cells and Pregnancy Complications

PROBLEM

Pregnancy complications such as spontaneous abortion, preeclampsia, and preterm birth persist, despite current interventions aimed at their prevention and treatment largely proving unsuccessful. Interleukin-27 (IL-27), composed of p28 and EBI3 subunits, binds to IL-27R, which consists of gp130 and IL-27Rα (also known as WSX-1 or TCCR), and plays a pivotal role in tumor development and inflammation regulation. At the maternal-fetal interface, IL-27 expression has been detected in trophoblasts, endometrial stromal cells, and decidual cells. Abnormal levels of IL-27/IL-27R have been linked to adverse pregnancy outcomes, including spontaneous miscarriage, preeclampsia, and preterm birth. This review aims to explore the expression of IL-27 at the maternal-fetal interface and its signaling pathway, uncovering the complex role of IL-27 in pregnancy complications.

METHOD OF STUDY

A comprehensive literature review was conducted using PubMed/Medline, Scopus, and Embase databases, analyzing studies on IL-27 expression and its signaling pathways at the maternal-fetal interface. The review focused on identifying the presence of IL-27 in various cell types and linking abnormal IL-27/IL-27R expression to pregnancy complications such as spontaneous miscarriage, preeclampsia, and preterm birth.

DISCUSSION AND CONCLUSION

IL-27 plays a complex role at the maternal-fetal interface, with abnormal expression linked to several pregnancy complications. These findings highlight the need for further research to elucidate IL-27's mechanisms and develop targeted interventions. Future studies should aim to develop targeted interventions and improve therapeutic strategies for managing pregnancy complications.

Extracellular vesicles as mediators of stress response in embryo-maternal communication

Introduction: The pivotal role of extracellular vesicles (EVs) in facilitating effective communication between the embryo and maternal cells during the preimplantation stage of pregnancy has been extensively explored. Nonetheless, inquiries persist regarding the alterations in EV cargo from endometrial cells under stress conditions and its potential to elicit specific stress responses in trophoblast cells. Thus, the aim of this study was to elucidate the involvement of EV miRNA miRNAs in transmitting stress signals from maternal cells to trophoblasts. Methods: The receptive endometrial epithelium analogue RL95-2 cells were subjected to stress induction with 200 µM CoCl2 for 24 h before EV isolation. JAr trophoblast spheroids, which serve as embryos, were subjected to treatment with stressed or unstressed EVs derived from RL95-2 cells for 24 h. Transcriptomic alterations in the treated JAr spheroids as well as in the untreated group, as a negative control, were investigated by mRNA sequencing. Furthermore, the changes in EV miRNAs were assessed by sequencing EV samples. Results: A comprehensive analysis comparing the miRNA profiles between stressed and unstressed EVs revealed significant changes in 25 miRNAs. Furthermore, transcriptomic analysis of JAr spheroids treated with stressed RL95-2EVs versus unstressed EVs or the untreated group demonstrated 6 and 27 differentially expressed genes, respectively. Pathway enrichment analysis showed that stressed EVs induce alterations in gene expression in trophoblast cells, which is partially mediated by EV microRNAs. Discussion: Our results suggest that EVs can transfer stress signals from endometrial cells to the embryo. These discoveries shed new light on the mechanism underlying implantation failures under stress conditions. Unraveling the role of EVs in transmitting stress signals, can extend our knowledge to pave the way for targeted interventions to manage stress-related implantation failures.

Evaluation of the maternal systemic immune system during frozen euploid embryo transfer according to cycle outcome

Infertility affects 15 % of couples in the US, and many turn to assisted reproductive technologies, including in vitro fertilization and subsequent frozen embryo transfer (FET) to become pregnant. This study aimed to perform a broad assessment of the maternal immune system to determine if there are systemic differences on the day of FET in cycles that result in a live birth compared to those that do not. Women undergoing FET of euploid embryos were recruited and blood was collected on the day of FET as well as at early timepoints in pregnancy. Sixty immune and angiogenic proteins were measured in plasma, and gene expression of 92 immune-response related genes were evaluated in peripheral blood mononuclear cells (PBMCs). We found plasma concentrations of interleukin-13 (IL-13) and macrophage derived chemokine (MDC) were significantly lower on the day of FET in cycles that resulted in a live birth. We also found genes encoding C-C chemokine receptor type 5 (CCR5), CD8 subunit alpha (CD8A) and SMAD family member 3 (SMAD3) were upregulated in PBMCs on the day of FET in cycles that resulted in live birth. Measurements of immune mediators from maternal blood could serve as prognostic markers during FET to guide clinical decision making and further our understanding of implantation failure.

A Comprehensive Review of the Endometrial Receptivity Array in Embryo Transfer: Advancements, Applications, and Clinical Outcomes

Embryo transfer is a pivotal procedure in assisted reproductive technologies (ART). Yet, the success of this process hinges on multiple factors, with endometrial receptivity playing a critical role in determining the likelihood of successful implantation. The endometrial receptivity array (ERA) is an advanced diagnostic tool designed to personalize embryo transfer timing by assessing the endometrium's receptivity. This review comprehensively examines the ERA, exploring its biological foundation, technological development, and clinical applications. The ERA's ability to analyze the expression of genes associated with endometrial receptivity offers a tailored approach to identifying the optimal window of implantation (WOI), particularly benefiting patients with recurrent implantation failure (RIF) or repeated unsuccessful in vitro fertilization (IVF) cycles. Clinical outcomes from ERA-guided embryo transfers indicate improvements in implantation rates and overall pregnancy success, although challenges such as result variability and cost-effectiveness persist. This review also discusses the latest advancements in ERA technology, including integrating genomic and transcriptomic analyses, non-invasive techniques, and using artificial intelligence (AI). Controversies regarding the widespread application of ERA and its necessity in all IVF cases are critically examined. By summarizing the current state of ERA in embryo transfer, this review aims to inform clinicians, researchers, and patients about its potential to enhance ART outcomes and to highlight areas for future research and innovation.

Bioengineering-tissue strategies to model mammalian implantation in vitro

During mammalian implantation, complex and well-orchestrated interactions between the trophectoderm of implanting blastocysts and the maternal endometrium lead to a successful pregnancy. On the other hand, alteration in endometrium-blastocyst crosstalk often causes implantation failure, pregnancy loss, and complications that result in overall infertility. In domestic animals, this represents one of the major causes of economic losses and the understanding of the processes taking place during the early phases of implantation, in both healthy and pathological conditions, is of great importance, to enhance livestock system efficiency. Here we develop highly predictive and reproducible functional tridimensional (3D) in vitro models able to mimic the two main actors that play a key role at this developmental stage: the blastocyst and the endometrium. In particular, we generate a 3D endometrial model by co-culturing primary epithelial and stromal cells, isolated from sow uteri, onto highly porous polystyrene scaffolds. In parallel, we chemically reprogram porcine adult dermal fibroblasts and encapsulate them into micro-bioreactors to create trophoblast (TR) spheroids. Finally, we combine the generated artificial endometrium with the TR spheroids to model mammalian implantation in vitro and mimic the embryo-maternal interactions. The protocols here described allow the generation of reproducible and functional 3D models of both the maternal compartment as well as the implanting embryo, able to recreate in vitro the architecture and physiology of the two tissues in vivo. We suggest that these models can find useful applications to further elucidate early implantation mechanisms and to study the complex interactions between the maternal tissue and the developing embryos.

A new insight into the pathway behind spontaneous recurrent pregnancy loss: decreased CYR61 gene expression

OBJECTIVE

Investigating the potential role of CYR61 in recurrent pregnancy loss is critical for developing diagnostic approaches and treatments for recurrent pregnancy loss.

METHODS

In this prospective case-control study, we have investigated the expression patterns of CYR61 in blood samples from participants with recurrent pregnancy loss in their medical history and control group (n=20 vs n=10). Peripheral blood mononuclear cells from study and control groups were isolated and the expression patterns of the CYR61 gene were determined by real-time semi-quantitative reverse transcriptase PCR.

RESULTS

A significant decrease in CYR61 gene expression was demonstrated in patients with two or more clinically recognized miscarriages compared with patients without miscarriages or with a history of miscarriage (p<0.01), which may make the CYR61 gene a potential candidate for predicting the risk of recurrent pregnancy loss.

DISCUSSION

This study provides a basis for a detailed investigation of candidate biomarkers and molecular players involved in the development of recurrent pregnancy loss and for the development of potential treatment approaches to prevent recurrent pregnancy loss.

Behind the Curtain of Abnormal Placentation in Pre-Eclampsia: From Molecular Mechanisms to Histological Hallmarks

Successful human pregnancy needs several highly controlled steps to guarantee an oocyte's fertilization, the embryo's pre-implantation development, and its subsequent implantation into the uterine wall. The subsequent placenta development ensures adequate fetal nutrition and oxygenation, with the trophoblast being the first cell lineage to differentiate during this process. The placenta sustains the growth of the fetus by providing it with oxygen and nutrients and removing waste products. It is not surprising that issues with the early development of the placenta can lead to common pregnancy disorders, such as recurrent miscarriage, fetal growth restriction, pre-eclampsia, and stillbirth. Understanding the normal development of the human placenta is essential for recognizing and contextualizing any pathological aberrations that may occur. The effects of these issues may not become apparent until later in pregnancy, during the mid or advanced stages. This review discusses the process of the embryo implantation phase, the molecular mechanisms involved, and the abnormalities in those mechanisms that are thought to contribute to the development of pre-eclampsia. The review also covers the histological hallmarks of pre-eclampsia as found during the examination of placental tissue from pre-eclampsia patients.

Reference Ranges of 2-Dimensional Placental Biometry and 3-Dimensional Placental Volume between 11 and 14 Weeks of Gestation

OBJECTIVE

The purpose of this study was to provide gestational age (GA) specific reference ranges for 2-dimensional (2D) placental biometry and 3-dimensional (3D) placental volume between 11 and 14 weeks of gestation.

METHODS

Placental biometry including 2D and 3D variables was calculated in 1142 first-trimester singleton pregnancies with non-complicated outcome between September 2016 and February 2020. Ultrasound datasets were obtained at the time of the first-trimester ultrasound, and 2D basal plate (BP), chorionic plate (CP), placental thickness (PT), and 3D placental volume (PV) were measured following a standardized methodology. Reference ranges for each variable were calculated according to GA and crown-rump-length (CRL).

RESULTS

A total of 1142 uncomplicated pregnancies were considered for analysis. All placental measurements increased significantly between 11 and 14 weeks, especially for PT (39.64%) and PV (64.4%). Reference ranges were constructed for each 2D and 3D first-trimester placental variable using the best-fit regression model for the predicted mean and SD as a function of GA and CRL.

CONCLUSIONS

Reference ranges of 2D placental biometry and 3D placental volume between 11 and 14 weeks of gestation were constructed, generating reference values. Placental biometry showed a progressive increase during the first trimester. This highlights the importance of using reference range charts according to GA.

Do extracellular vesicles have specific target cells?; Extracellular vesicle mediated embryo maternal communication

Extracellular vesicles (EVs) serve as messengers for intercellular communication, yet the precise mechanisms by which recipient cells interpret EV messages remain incompletely understood. In this study, we explored how the origin of EVs, their protein cargo, and the recipient cell type influence the cellular response to EVs within an embryo implantation model. We treated two types of EVs to 6 different recipient cell types and expression of zinc finger protein 81 (ZNF81) gene expression in the recipient cells were quantified using quantitative polymerase chain reaction (qPCR). The proteomic contents of the EV cargos were also analyzed. The results showed that downregulation of the ZNF81 gene was a specific cellular response of receptive endometrial epithelial cells to trophoblast derived EVs. Protein cargo analysis revealed that the proteomic profile of EVs depends on their cell of origin and therefore may affect the recipient cell response to EVs. Furthermore, trophoblastic EVs were found to be specifically enriched with transcription factors such as CTNNB1 (catenin beta-1), HDAC2 (histone deacetylase 2), and NOTCH1 (neurogenic locus notch homolog protein 1), which are known regulators of ZNF81 gene expression. The current study provided compelling evidence supporting the existence of EV specificity, where the characteristics of both the EVs and the recipient cell type collectively contribute to regulating EV target specificity. Additionally, EV protein cargo analysis suggested a potential association between transcription factors and the specific functionality of trophoblastic EVs. This in vitro embryo implantation model and ZNF81 read-out provides a unique platform to study EV specific functionality in natural cell-cell communication.

Correlation Between Maternal-Fetus Interface and Placenta-Mediated Complications

Pregnancy is a highly regulated biological phenomenon that involves the development of a semi-allogeneic fetus inside the uterus of the mother. The maternal-fetal interface is a critical junction where communication takes place between the fetal and maternal immune systems, which determine the outcome of the pregnancy. The interface is composed of the decidua and placenta. The main cells present at the maternal-fetal interface include invading trophoblasts, maternal immune cells, and decidual stromal cells. Although maternal tolerance is crucial for maintaining a successful pregnancy, the role of the placenta in pregnancy is also important. Dysregulation of the placenta leads to various placenta-mediated complications, such as preeclampsia, intrauterine growth restriction, and placental abruption. Although the exact mechanism involving these complications is unclear, research has elucidated various factors involved in these pregnancy disorders. This review aimed to provide a summary of the maternal-fetal interface and immune mechanisms involved in placenta-mediated complications.

Management guidelines for incidental uterine surgery in early pregnancy: a case report of a robotic myomectomy at 4 weeks gestation after a false-negative pregnancy test

Objective

To share our case and offer guidance to practitioners on the management of incidental uterine surgery in early pregnancy. Although elective uterine surgery should be avoided during pregnancy, there is always a chance of undetected pregnancy at the time of surgery, even after all precautions have been taken. There is currently minimal literature on the management and outcomes of uterine surgery during pregnancy.

Design

Case report.

Setting

University Hospital.

Patient

A 42-year-old G1P1 female with symptomatic fibroids desiring fertility-sparing surgery was retroactively found to be 4 weeks pregnant at the time of surgery, even after a negative pregnancy test and low suspicion for pregnancy under Centers for Disease Control and Prevention guidelines.

Intervention

Robotic-assisted laparoscopic myomectomy performed with a false-negative urine pregnancy test at the time of surgery.

Main Outcome Measures

Guidance for surveillance and management options during continued pregnancy after robotic uterine surgery and cavity disruption by a uterine manipulator performed at 4 weeks gestation that went undetected at the time of surgery.

Results

The patient was able to undergo an uncomplicated delivery by cesarean section at 38 weeks and delivered a healthy infant.

Conclusion

Using a multidisciplinary approach, we describe guidelines for antepartum surveillance uterine surgery during an undetected pregnancy, which resulted in the delivery of a term healthy infant.

HB-EGF-loaded nanovesicles enhance trophectodermal spheroid attachment and invasion

The ability of trophectodermal cells (outer layer of the embryo) to attach to the endometrial cells and subsequently invade the underlying matrix are critical stages of embryo implantation during successful pregnancy establishment. Extracellular vesicles (EVs) have been implicated in embryo-maternal crosstalk, capable of reprogramming endometrial cells towards a pro-implantation signature and phenotype. However, challenges associated with EV yield and direct loading of biomolecules limit their therapeutic potential. We have previously established generation of cell-derived nanovesicles (NVs) from human trophectodermal cells (hTSCs) and their capacity to reprogram endometrial cells to enhance adhesion and blastocyst outgrowth. Here, we employed a rapid NV loading strategy to encapsulate potent implantation molecules such as HB-EGF (NVHBEGF). We show these loaded NVs elicit EGFR-mediated effects in recipient endometrial cells, activating kinase phosphorylation sites that modulate their activity (AKT S124/129, MAPK1 T185/Y187), and downstream signalling pathways and processes (AKT signal transduction, GTPase activity). Importantly, they enhanced target cell attachment and invasion. The phosphoproteomics and proteomics approach highlight NVHBEGF-mediated short-term signalling patterns and long-term reprogramming capabilities on endometrial cells which functionally enhance trophectodermal-endometrial interactions. This proof-of-concept study demonstrates feasibility in enhancing the functional potency of NVs in the context of embryo implantation.

Is there a treatable cause of repeated implantation failure, or is it simply treatment failure by chance?

RESEARCH QUESTION

Does repeated implantation failure (RIF) sometimes have a cause, or is it simply treatment failure by chance?

DESIGN

A hypothetical model of a cohort of 1000 women undergoing four repeated IVF attempts was constructed. A proportion of women with RIF carried an underlying risk factor negatively affecting implantation, compared with women without the factor. In strategy A, women had standard IVF without additional treatment; in strategy B, the women received standard IVF plus an additional treatment. The sensitivity analysis varied the prevalence of the underlying risk factor from 5% to 50%. The model was compared with literature studies where a treatment strategy had been applied.

RESULTS

With strategy A, the clinical pregnancy rate decreased with subsequent IVF attempts (31% in the first transfer with a risk factor prevalence of 5%, to 8% in the fourth transfer with a risk factor prevalence of 50%). As the prevalence increased, the clinical pregnancy rate was higher with strategy A. For strategy B, the clinical pregnancy rates for the modelled cohort decreased with each subsequent IVF attempt. Regardless of the prevalence of the risk factor, the decline in clinical pregnancy rate was less strong (from 32% in the first transfer with a prevalence of 5%, to 25% in the fourth transfer with a prevalence of 50%). When applying the model to the literature studies, the trends expected for strategy B (decreasing clinical pregnancy rates) were not expressed.

CONCLUSIONS

RIF might therefore be of iatrogenic origin due to the low success rate of IVF and might be triggered by the increasing female age associated with higher numbers of RIF.

Effect of 3D and 2D cell culture systems on trophoblast extracellular vesicle physico-chemical characteristics and potency

The growing understanding of the role of extracellular vesicles (EVs) in embryo-maternal communication has sparked considerable interest in their therapeutic potential within assisted reproductive technology, particularly in enhancing implantation success. However, the major obstacle remains the large-scale production of EVs, and there is still a gap in understanding how different culture systems affect the characteristics of the EVs. In the current study, trophoblast analogue human chorionic carcinoma cell line was cultivated in both conventional monolayer culture (2D) and as spheroids in suspension culture (3D) and how the cell growth environment affects the physical, biochemical and cellular signalling properties of EVs produced by them was studied. Interestingly, the 3D system was more active in secreting EVs compared to the 2D system, while no significant differences were observed in terms of morphology, size, and classical EV protein marker expression between EVs derived from the two culture systems. There were substantial differences in the proteomic cargo profile and cellular signalling potency of EVs derived from the two culture systems. Notably, 2D EVs were more potent in inducing a cellular response in endometrial epithelial cells (EECs) compared to 3D EVs. Therefore, it is essential to recognize that the biological activity of EVs depends not only on the cell of origin but also on the cellular microenvironment of the parent cell. In conclusion, caution is warranted when selecting an EV production platform, especially for assessing the functional and therapeutic potential of EVs through in vitro studies.

Effects of Variable Embryo Transfer on the Variable Window of Implantation and Analysis of Pregnancy Outcomes

Background A descriptive analysis of patients who underwent various embryo transfer methods to address the root cause of their infertility at a tertiary infertility care complex in Wardha, India, is presented herein. This analysis aims to evaluate the management of infertility and assess pregnancy outcomes. Methodology We conducted a retrospective cohort study on patients who underwent various embryo transfer methods to address the cause of their infertility, specifically focusing on a variable window of implantation (WOI) at a tertiary infertility clinic over a one-year period. The medical records of 11 patients in both the variable embryo transfer (VET) and control groups were reviewed and analyzed for this article. Results The examination of medical records revealed a significant improvement in the rate of implantation (p-value = 0.04) and clinical pregnancy outcomes (p-value = 0.03) among patients who underwent VET. Comparable statistical outcomes were observed for other variables of pregnancy outcome, including miscarriage rate, multiple pregnancy rate, and biochemical pregnancy rate. Conclusion This retrospective cohort study suggests that the utilization of VET could be a viable option for women experiencing recurrent implantation failure cycles, particularly when an adequate number of embryos are available. This is owing to the challenges in clinically diagnosing a variable WOI. Further studies with a significantly larger sample population are recommended to validate the results and integrate this approach into the standard operating procedures, aiming to enhance the likelihood of pregnancy in these populations.

Enhancing endometrial receptivity: the roles of human chorionic gonadotropin in autophagy and apoptosis regulation in endometrial stromal cells

Inadequate endometrial receptivity often results in embryo implantation failure and miscarriage. Human chorionic gonadotropin (hCG) is a key signaling molecule secreted during early embryonic development, which regulates embryonic maternal interface signaling and promotes embryo implantation. This study aimed to examine the impact of hCG on endometrial receptivity and its underlying mechanisms. An exploratory study was designed, and endometrial samples were obtained from women diagnosed with simple tubal infertility or male factor infertile (n = 12) and recurrent implantation failure (RIF, n = 10). Using reverse transcription-quantitative PCR and western blotting, luteinizing hormone (LH)/hCG receptor (LHCGR) levels and autophagy were detected in the endometrial tissues. Subsequently, primary endometrial stromal cells (ESCs) were isolated from these control groups and treated with hCG to examine the presence of LHCGR and markers of endometrial receptivity (HOXA10, ITGB3, FOXO1, LIF, and L-selectin ligand) and autophagy-related factors (Beclin1, LC3, and P62). The findings revealed that the expressions of receptivity factors, LHCGR, and LC3 were reduced in the endometrial tissues of women with RIF compared with the control group, whereas the expression of P62 was elevated. The administration of hCG to ESCs specifically activated LHCGR, stimulating an increase in the endometrial production of HOXA10, ITGB3, FOXO1, LIF and L-selectin ligands. Furthermore, when ESCs were exposed to 0.1 IU/mL hCG for 72 h, the autophagy factors Beclin1 and LC3 increased within the cells and P62 decreased. Moreover, the apoptotic factor Bax increased and Bcl-2 declined. However, when small interfering RNA was used to knock down LHCGR, hCG was less capable of controlling endometrial receptivity and autophagy molecules in ESCs. In addition, hCG stimulation enhanced the phosphorylation of ERK1/2 and mTOR proteins. These results suggest that women with RIF exhibit lower levels of LHCGR and compromised autophagy function in their endometrial tissues. Thus, hCG/LHCGR could potentially improve endometrial receptivity by modulating autophagy and apoptosis.

Intra-individual variability of serum progesterone levels on the day of frozen blastocyst transfer in hormonal replacement therapy cycles

STUDY QUESTION

Is there a significant intra-individual variability of serum progesterone levels on the day of single blastocyst Hormone Replacement Therapy-Frozen Embryo Transfer (HRT-FET) between two consecutive cycles?

SUMMARY ANSWER

No significant intra-individual variability of serum progesterone (P) levels was noted between two consecutive HRT-FET cycles.

WHAT IS KNOWN ALREADY

In HRT-FET cycles, a minimum P level on the day of embryo transfer is necessary to optimise reproductive outcomes. In a previous study by our team, a threshold of 9.8 ng/ml serum P was identified as significantly associated with the live birth rates in single autologous blastocyst transfers under HRT using micronized vaginal progesterone (MVP). Such patients may benefit from an intensive luteal phase support (LPS) using other routes of P administration in addition to MVP. A crucial question in the way towards individualising LPS is whether serum P measurements are reproducible for a given patient in consecutive HRT-FET cycles, using the same LPS.

STUDY DESIGN, SIZE, DURATION

We conducted an observational cohort study at the university-based reproductive medicine centre of our institution focusing on women who underwent at least two consecutive single autologous blastocyst HRT-FET cycles between January 2019 and March 2020.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients undergoing two consecutive single autologous blastocyst HRT-FET cycles using exogenous oestradiol and vaginal micronized progesterone for endometrial preparation were included. Serum progesterone levels were measured on the morning of the Frozen Embryo Transfer (FET), by a single laboratory. The two measurements of progesterone levels performed on the day of the first (FET1) and the second FET (FET2) were compared to evaluate the intra-individual variability of serum P levels. Paired statistical analyses were performed, as appropriate.

MAIN RESULTS AND THE ROLE OF CHANCE

Two hundred and sixty-four patients undergoing two consecutive single autologous blastocyst HRT-FET were included. The mean age of the included women was 35.0 ± 4.2 years. No significant intra-individual variability was observed between FET1 and FET2 (mean progesterone level after FET1: 13.4 ± 5.1 ng/ml vs after FET2: 13.9 ± 5.0; P = 0.08). The characteristics of the embryo transfers were similar between the first and the second FET. Forty-nine patients (18.6%) had discordant progesterone levels (defined as one progesterone measurement > and one ≤ to the threshold of 9.8 ng/ml) between FET1 and FET2. There were 37/264 women (14.0%) who had high intra-individual variability (defined as a difference in serum progesterone values >75th percentile (6.0 ng/ml)) between FET1 and FET2. No specific clinical parameter was associated with a high intra-individual variability nor a discordant P measurement.

LIMITATIONS, REASONS FOR CAUTION

This study is limited by its retrospective design. Moreover, only women undergoing autologous blastocyst HRT-FET with MVP were included, thereby limiting the extrapolation of the study findings to other routes of P administration and other kinds of endometrial preparation for FET.

WIDER IMPLICATIONS OF THE FINDINGS

No significant intra-individual variability was noted. The serum progesterone level appeared to be reproducible in >80% of cases. These findings suggest that the serum progesterone level measured on the day of the first transfer can be used to individualize luteal phase support in subsequent cycles.

STUDY FUNDING/COMPETING INTEREST(S)

No funding or competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Simple method for isolation and culture of primary buffalo (Bubalus bubalis) endometrial epithelial cells (pBuEECs) and its characterization using high throughput proteomics approach

Early embryonic mortality resulting from insufficient interaction between the embryo and the uterus leads to the failure of pregnancy in livestock animals. Thus, it is imperative to comprehend the multifaceted process of implantation at molecular levels, which requires synchronized feto-maternal interaction. The in-vitro models serve as valuable tools to investigate the specific stages of implantation. The present study was undertaken to develop a simple method to isolate and culture the primary buffalo endometrial epithelial cells (pBuEECs), followed by proteome profiling of the proliferating cells. Collagenase I was used to separate uterine epithelial cells (UECs) from the ipsilateral uterine horn, and then the cells were separated using a cell strainer. After being seeded on culture plates, UECs developed colonies with characteristic epithelial shape and expressed important markers such as cytokeratin 18 (KRT18), progesterone receptor (PGR), β-estrogen receptor (ESR1), and leukemia inhibitory factor (LIF), which were confirmed by PCR. The purity of epithelial cells was assessed using cytokeratin 18 immunostaining, which indicated approximately 99% purity in cultured cells. The proteome profiling of pBuEECs via high-throughput tandem mass spectrometry (MS), identified a total of 3383 proteins. Bioinformatics analysis revealed enrichment in various biological processes, including cellular processes, metabolic processes, biological regulation, localization, signaling, and developmental processes. Moreover, the KEGG pathway analysis highlighted associations with the ribosome, proteosome, oxidative phosphorylation, spliceosome, and cytoskeleton regulation pathways. In conclusion, these well characterized cells offer valuable in-vitro model to enhance the understanding of implantation and uterine pathophysiology in livestock animals, particularly buffaloes.

Detrimental effects of electromagnetic radiation emitted from cell phone on embryo morphokinetics and blastocyst viability in mice

Electromagnetic radiation (EMR) has deleterious effects on sperm motility and viability, as well as oocyte membrane and organelle structure. The aim was to assess the effects of cell phone radiation on preimplantation embryo morphokinetics and blastocyst viability in mice. For superovulation, 20 female mice were treated with intraperitoneal (IP) injections of 10 IU pregnant mare's serum gonadotropin (Folligon® PMSG), followed by 10 IU of human chorionic gonadotropin (hCG) after 48 h. The zygotes (n = 150) from the control group were incubated for 4 days. The experimental zygotes (n = 150) were exposed to a cell phone emitting EMR with a frequency range 900-1800 MHz for 30 min on day 1. Then, all embryos were cultured in the time-lapse system and annotated based on time points from the 2-cell stage (t2) to hatched blastocyst (tHDyz), as well as abnormal cleavage patterns. Blastocyst viability was assessed using Hoechst and propidium iodide staining. Significant increases (P < 0.05) were observed in the cleavage division time points of t2, t8, t10, and t12 of the experimental group compared with the controls. In terms of blastocyst formation parameters, a delay in embryo development was observed in the experimental group compared with the controls. Data analysis of the time intervals between the two groups showed a significant difference in the s3 time interval (P < 0.05). Also, the rates of fragmentation, reverse cleavage, vacuole formation, and embryo arrest were significantly higher in the experimental group (P < 0.05). Furthermore, the cell survival rate in the experimental group was lower than the control group (P < 0.05). Exposure to EMR has detrimental consequences for preimplantation embryo development in mice. These effects can manifest as defects in the cleavage stage and impaired blastocyst formation, leading to lower cell viability.

A Narrative Review on the Impact of Smoking on Female Fertility

Understanding the significant impact of preventable factors, such as lifestyle decisions and bad habits like smoking, on female fertility has received a lot of attention. Pervasive smoking among fertile women is a serious public health concern. Smoking has well-documented negative impacts on general health, but it also has significant consequences on fertility. Many women of reproductive age still smoke, despite a wealth of data elucidating the effects of pregnancy and the health of the fetus as a result of prenatal exposure. This review attempts to investigate the consequences of smoking on female fertility, specifically focusing on how it affects the ovaries, oviducts, and uterus through a thorough examination of numerous studies. Important topics such as ovarian reserve, steroidogenesis, ovulation, controlling the menstrual cycle, oviductal function, uterine receptivity, and implantation will receive extra focus.

Unveiling the Role of Endometrial CD-138: A Comprehensive Review on Its Significance in Infertility and Early Pregnancy

This review comprehensively examines the role of endometrial CD-138 (syndecan-1) in the context of infertility and early pregnancy. The endometrium, a dynamic tissue responsive to hormonal cues, plays a central role in fertility, and understanding the molecular intricacies governing its function is crucial. CD-138, a cell surface proteoglycan, emerges as a critical player expressed by various endometrial cell types. Our exploration encompasses a brief overview of the endometrium, introducing CD-138 as a significant molecular entity. The rationale for the review underscores the importance of elucidating endometrial factors in fertility and addresses existing knowledge gaps related to CD-138. Throughout the review, we unravel the multifaceted nature of CD-138 and its involvement in infertility, highlighting its potential as a diagnostic marker. Furthermore, insights into CD-138's role during early pregnancy, including trophoblast-endothelial interactions, are discussed. In conclusion, the findings underscore the clinical implications of CD-138, suggesting its utility in diagnostics and offering prospects for targeted therapeutic interventions. The identified knowledge gaps propel future research directions, promising to deepen our understanding of this enigmatic molecule and its transformative potential in reproductive medicine.

A Case Series Based on the Mixed Double-Embryo Transfer (MDET) Outcome in Patients With Recurrent Implantation Failure

Successful implantation of embryos depends on the synchronous cross-talks between the endometrial wall and the competent blastocyst within the window of implantation (WOI). Hence, the WOI has a major significance in assisted reproductive technology (ART). However, in some cases, women do not have fixed WOI in ART cycles in order to enhance the rate of successful clinical pregnancy. However, there have been stances where women do not have a fixed WOI, and it shifts in subsequent menstrual periods. This contributes to the chances of recurrent implantation failure (RIF). Another factor that contributes to RIF is erratic endometrial receptivity, which hinders the chances of successful implantation of the conceptus in the endometrium. This case series consists of four case studies where the patients were believed to be suffering from RIF due to variable WOI or erratic endometrial receptivity and the routine protocol followed nowadays failed to make them conceive. In order to resolve the condition, we proposed a novel strategy in an attempt to improve pregnancy rates in these cases. An innovative method of embryo transfer known as mixed double-embryo transfer (MDET), which involved the transfer of one day 3 embryo and one day 5 blastocyst on day 6 of progesterone, led to possible pregnancy outcomes. A viable pregnancy was validated based on the human chorionic gonadotropin (β-hCG) test report, and two of the cases delivered healthy babies. Thus, this case series provides a unique approach to addressing the issues of RIF. However, larger studies are required to validate the possible use of this technique.

FOXM1 Participates in Trophoblast Migration and Early Trophoblast Invasion: Potential Role in Blastocyst Implantation

Successful implantation requires coordinated migration and invasion of trophoblast cells into a receptive endometrium. Reduced forkhead box M1 (FOXM1) expression limits trophoblast migration and angiogenesis in choriocarcinoma cell lines, and in a rat model, placental FOXM1 protein expression was significantly upregulated in the early stages of pregnancy compared to term pregnancy. However, the precise role of FOXM1 in implantation events remains unknown. By analyzing mice blastocysts at embryonic day (E3.5), we have demonstrated that FOXM1 is expressed as early as the blastocyst stage, and it is expressed in the trophectoderm of the blastocyst. Since controlled oxygen tension is determinant for achieving normal implantation and placentation and a chronic hypoxic environment leads to shallow trophoblast invasion, we evaluated if FOXM1 expression changes in response to different oxygen tensions in the HTR-8/SVneo first trimester human trophoblast cell line and observed that FOXM1 expression was significantly higher when trophoblast cells were cultured at 3% O2, which coincides with oxygen concentrations in the uteroplacental interface at the time of implantation. Conversely, FOXM1 expression diminished in response to 1% O2 that resembles a hypoxic environment in utero. Migration and angiogenesis were assessed following FOXM1 knockdown and overexpression at 3% O2 and 1% O2, respectively, in HTR-8/SVneo cells. FOXM1 overexpression increased transmigration ability and tubule formation. Using a 3D trophoblast invasion model with trophospheres from HTR-8/SVneo cells cultured on a layer of MATRIGEL and of mesenchymal stem cells isolated from menstrual fluid, we observed that trophospheres obtained from 3D trophoblast invasion displayed higher FOXM1 expression compared with pre-invasion trophospheres. Moreover, we have also observed that FOXM1-overexpressing trophospheres increased trophoblast invasion compared with controls. HTR-8/SVneo-FOXM1-depleted cells led to a downregulation of PLK4, VEGF, and MMP2 mRNA expression. Our current findings suggest that FOXM1 participates in embryo implantation by contributing to trophoblast migration and early trophoblast invasion, by inducing transcription activation of genes involved in these processes. Maternal-fetal communication is crucial for trophoblast invasion, and maternal stromal cells may induce higher levels of FOXM1 in trophoblast cells.

Non-coding RNAs in Recurrent implantation failure

Recurrent implantation failure (RIF), defined as the inability to achieve conception following multiple consecutive in-vitro fertilization (IVF) attempts, represents a complex and multifaceted challenge in reproductive medicine. The emerging role of non-coding RNAs in RIF etiopathogenesis has only gained prominence over the last decade, illustrating a new dimension to our understanding of the intricate network underlying RIF. Successful embryo implantation demands a harmonious synchronization between an adequately decidualized endometrium, a competent blastocyst, and effective maternal-embryonic interactions. Emerging evidence has clarified the involvement of a sophisticated network of non-coding RNAs, including microRNAs, circular RNAs, and long non-coding RNAs, in orchestrating these pivotal processes. Disconcerted expression of these molecules can disrupt the delicate equilibrium required for implantation, amplifying the risk of RIF. This comprehensive review presents an in-depth investigation of the complex role played by non-coding RNAs in the pathogenesis of RIF. Furthermore, it underscores the vast potential of non-coding RNAs as diagnostic biomarkers and therapeutic targets, with the ultimate goal of enhancing implantation success rates in IVF cycles. As ongoing research continues to unravel the intercalated web of molecular interactions, exploiting the power of non-coding RNAs may offer promising avenues for mitigating the challenges posed by RIF and improving the outcomes of assisted reproduction.

The Effect of Superoxide Dismutase Mimetic Drug in an Infertile Patient With Thin Endometrium

It has been observed that nowadays, millions of couples struggle with infertility, which may be attributed to various conditions. In this case study, a middle-aged couple with a history of recurrent implantation failure (RIF) visited an infertility clinic situated in a rural region in Wardha to seek treatment. The male was normozoospermic. After hysteroscopy, it was noticed that an aggregated level of reactive oxygen species (ROS) was a causative factor for thin endometrium contributing to infertility. The patient was advised to autologous platelet-rich plasma (PRP) treatment and temporary medication. A significant level of amelioration in endometrial thickness was observed, which significantly contributed to the chances of implantation. This resulted in a positive clinical pregnancy outcome for the patient. This case report highlights the fact that a combination of tempol with autologous PRP may contribute to an improved factor for the enhancement of endometrial hyperplasia, which may contribute to an improved in vitro fertilization (IVF) pregnancy outcome.

Role of Platelet-rich Plasma in Unexplained Recurrent Implantation Failure - A Systematic Review and Meta-analysis of Randomised Control Trials

Background

Recurrent implantation failure (RIF) is a challenging clinical situation and various strategies have been tried to improve the pregnancy rate in RIF. Platelet-rich plasma (PRP), which is obtained from the autologous blood samples of a person and is multiple times richer in platelets and other growth factors helps improve endometrial receptivity.

Objective

This study has been conducted to summarise the evidence and quality of evidence available so far regarding the role of PRP in cases of unexplained RIF.

Materials and Methods

An electronic database search for randomised clinical trials comparing PRP against routine care in women with unexplained RIF was performed on PubMed, EMBASE, SCOPUS and Cochrane Central. Two independent reviewers conducted a literature search and retrieved data using the predefined eligibility criteria. Bias assessment was done using the Cochrane Collaboration Network Risk of Bias Tool version 2. The quality of evidence was determined and a summary of the findings table was prepared for individual outcomes using GRADEpro software.

Results

We identified 1146 records, and after removing duplicates, 531 records were screened. Out of these, 22 studies reached full-text screening and nine studies were included in the final review. We are uncertain about the effect of PRP due to the very low quality of evidence and we have little confidence that the administration of PRP had any significant effect on improving the live birth rate in women with RIF (odds ratio [OR]: 7.32, 95% confidence interval [CI]: 4.54-11.81, I2 = 40%). Similarly, the quality of evidence was low for the clinical pregnancy rate, so we are uncertain if the administration of PRP had any significant effect on the clinical pregnancy rate (OR: 3.20, 95% CI: 2.38-4.28, I2 = 0%).

Interpretation

The current review suggests that there may be some beneficial effects of PRP in women with RIF, but the quality of evidence is very low and we are uncertain of the benefit and have little confidence in these findings.

Limitations

Limitations are the small sample size of most studies, a short follow-up period, non-uniformity in the definition of outcomes and very low quality of evidence.

Registration

The protocol was registered on PROSPERO (CRD42021292209).

Placental single cell transcriptomics: Opportunities for endocrine disrupting chemical toxicology

The placenta performs essential biologic functions for fetal development throughout pregnancy. Placental dysfunction is at the root of multiple adverse birth outcomes such as intrauterine growth restriction, preeclampsia, and preterm birth. Exposure to endocrine disrupting chemicals during pregnancy can cause placental dysfunction, and many prior human studies have examined molecular changes in bulk placental tissues. Placenta-specific cell types, including cytotrophoblasts, syncytiotrophoblasts, extravillous trophoblasts, and placental resident macrophage Hofbauer cells play unique roles in placental development, structure, and function. Toxicant-induced changes in relative abundance and/or impairment of these cell types likely contribute to placental pathogenesis. Although gene expression insights gained from bulk placental tissue RNA-sequencing data are useful, their interpretation is limited because bulk analysis can mask the effects of a chemical on individual populations of placental cells. Cutting-edge single cell RNA-sequencing technologies are enabling the investigation of placental cell-type specific responses to endocrine disrupting chemicals. Moreover, in situ bioinformatic cell deconvolution enables the estimation of cell type proportions in bulk placental tissue gene expression data. These emerging technologies have tremendous potential to provide novel mechanistic insights in a complex heterogeneous tissue with implications for toxicant contributions to adverse pregnancy outcomes.

Understanding conceptus-maternal interactions: what tools do we need to develop?

Communication between the maternal endometrium and developing embryo/conceptus is critical to support successful pregnancy to term. Studying the peri-implantation period of pregnancy is critical as this is when most pregnancy loss occurs in cattle. Our current understanding of these interactions is limited, due to the lack of appropriate in vitro models to assess these interactions. The endometrium is a complex and heterogeneous tissue that is regulated in a transcriptional and translational manner throughout the oestrous cycle. While there are in vitro models to study endometrial function, they are static and 2D in nature or explant models and are limited in how well they recapitulate the in vivo endometrium. Recent developments in organoid systems, microfluidic approaches, extracellular matrix biology, and in silico approaches provide a new opportunity to develop in vitro systems that better model the in vivo scenario. This will allow us to investigate in a more high-throughput manner the fundamental molecular interactions that are required for successful pregnancy in cattle.

Uterine Arteries Resistance in Pregnant Women with Gestational Diabetes Mellitus, Diabetes Mellitus Type 1, Diabetes Mellitus Type 2, and Uncomplicated Pregnancies

BACKGROUND

The examination of the uterine arteries using Doppler in the first trimester of pregnancy serves as a valuable tool for evaluating the uteroplacental circulation. Diabetes mellitus is associated with altered placental implantation and pregnancy-related pathologies, such as preeclampsia. The aim of this study was to compare the uterine arteries' pulsatility indices (UtA PI) in women with diabetes mellitus type 1 (DM1), diabetes mellitus type 2 (DM2), gestational diabetes mellitus (GDM), and uncomplicated pregnancies.

METHODS

This was a retrospective case-control trial including pregnant women with DM1, DM2, GDM, and uncomplicated pregnancies, presenting for first-trimester ultrasound screening in two tertiary university hospitals between 2013 and 2023. The first-trimester UtA pulsatility index (PI), expressed in multiples of medians (MoMs), was compared between the four groups.

RESULTS

Out of 15,638 pregnant women, 58 women with DM1, 67 women with DM2, 65 women with GDM, and 65 women with uncomplicated pregnancies were included. The mean UtA PI were 1.00 ± 0.26 MoMs, 1.04 ± 0.32 MoMs, 1.02 ± 0.31 MoMs, and 1.08 ± 0.33 MoMs in pregnant women with DM1, DM2, GDM, and uncomplicated pregnancies, respectively (p > 0.05).

CONCLUSIONS

Potential alterations in the implantation of the placenta in pregnant women with diabetes were not displayed in the first-trimester pulsatility indices of the uterine arteries, as there were no changes between the groups.

FKBP5 regulates trophoblast-macrophage crosstalk in recurrent spontaneous abortion through PI3K/AKT and NF-κB signaling pathways

FK506-binding protein 5 (FKBP5) contributes to many diseases; However, it remains unclear whether FKBP5 is relevant to recurrent spontaneous abortion (RSA) and the mechanisms by which it is involved in maternal-fetal immunological tolerance. Placental tissue was collected in women with normal pregnancy and RSA and examined for FKBP5 expression. Human trophoblast cell lines and THP-1-derived M0 macrophages were used to explore the role of FKBP5 in RSA and its mechanism. The role of FKBP5 on pregnancy outcomes was assessed using a mouse model of miscarriage. This study found that upregulation of FKBP5 at the placental interface is involved in the pathogenesis of RSA by depressing trophoblast function and promoting M1-type macrophage polarization. First, FKBP5 expression was upregulated in the villi of RSA, and FKBP5 regulated trophoblast function by inhibiting HAPLN1 expression through suppression of PI3K/AKT signaling. In addition, FKBP5 inhibited trophoblast IL-6 secretion by suppressing PI3K/AKT signaling, thereby promoting macrophage polarization toward the M1 phenotype. Meanwhile, FKBP5 was significantly elevated in decidual macrophages from patients with RSA and promoted M1 macrophage polarization via ROS/NF-κB signaling and further inhibited trophoblast function. Finally, FKBP5 inhibitors improved embryo resorption rate in miscarried mice. In conclusion, FKBP5 is essential in maintaining pregnancy and trophoblast-macrophage crosstalk in the maternal-fetal interface, which may be a potential target for diagnosing and treating RSA.

Role of Endometrial Extracellular Vesicles in Mediating Cell-to-Cell Communication in the Uterus: A Review

There are several critical events that occur in the uterus during early pregnancy which are necessary for the establishment and maintenance of pregnancy. These events include blastocyst implantation, uterine decidualization, uterine neoangiogenesis, differentiation of trophoblast stem cells into different trophoblast cell lineages, and formation of a placenta. These processes involve several different cell types within the pregnant uterus. Communication between these cell types must be intricately coordinated for successful embryo implantation and the formation of a functional maternal-fetal interface in the placenta. Understanding how this intricate coordination transpires has been a focus of researchers in the field for many years. It has long been understood that maternal endometrial tissue plays a key role in intercellular signaling during early pregnancy, sending signals to nearby tissues in a paracrine manner. Recently, insights have been obtained into the mechanisms by which these signaling events occur. Notably, the endometrium has been shown to secrete extracellular vesicles (EVs) that contain crucial cargo (proteins, lipids, RNA, miRNA) that are taken up by recipient cells to initiate a response leading to the occurrence of critical events during implantation and placentation. In this review, we aim to summarize the role that endometrium-derived EVs play in mediating cell-to-cell communications within the pregnant uterus to orchestrate the events that must occur to establish and maintain pregnancy. We will also discuss how aberrant endometrial EV signaling may lead to pathophysiological conditions, such as endometriosis and infertility.

Study the effect of recombinant leukemia inhibitory factor on maintenance of pregnancy and frequency of regulatory T cells in abortion-prone mice

Recurrent spontaneous abortion (RSA) can have a significant impact on a woman's quality of life. Understanding the mechanisms behind abortion is crucial for developing potential treatments. Among various models of abortion, the CBA/J(♀) × DBA/2J(♂) model stands out as the most extensively studied. This model reveals the influence of an altered immune system on resorption during pregnancy. The leukemia inhibitory factor (LIF) holds considerable importance as a secretory glycoprotein essential for successful implantation. Regulatory T cells (Tregs) have been found to produce high levels of LIF in both mice and humans. LIF plays a vital role in the development of Tregs by upregulating the expression of the Foxp3 transcription factor while downregulating the expression of RORγt. To investigate the impact of recombinant LIF (rLIF) on pregnancy maintenance and Treg cell frequency in abortion-prone (AP) mice, a specific recombinant protein was used in this study. The AP group consisted of CBA/J(♀) × DBA/2J(♂) mice, while the control group comprised CBA/J(♀) × BALB/c(♂) mice. Intraperitoneal injections of rLIF were administered to the AP group on the third day of pregnancy, and its effects on Treg cell frequency and pregnancy maintenance were examined during this period. Following rLIF injections on the fourteenth day of pregnancy, the expression of Foxp3 significantly increased in AP mice (p = 0.02,0.008). Additionally, AP mice injected with rLIF demonstrated a significant reduction in resorption rate (p = 0.01) and a notable increase in birth rate (p = 0.01,0.0005). These findings provide new insights into the potential benefits of LIF in treating RSA patients.

Exploring the microbiome of two uterine sites in cows

Bacterial communities in the mammalian reproductive system can be rich and diverse, differing in structure and quantity depending on location. In addition, its microbiome is associated with the state of health of this tract and reproductive success. This study evaluated the microbiome composition of the uterine body (UB) and uterine horn mucosa (UH) samples using 16S rRNA sequencing of samples extracted from cows in the Amazon region. It was observed that four main phyla were shared between the uterine sites: Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Linear discriminant analysis effect size and heat tree analysis showed that members of Lachnospiraceae (NK3A20 group) and Oscillospiraceae were significantly more abundant in the UB than in UH. In addition, there are more unique genera in the UB than in the UH. A higher bacterial load in UB than in UH is expected because of the exposure to external factors of UB. However, comparing the site's communities through beta diversity did not generate well-defined clustering. Thus, it can be attributed to the closeness of the sites, which would make the niches similar ecologically and microbiologically. Therefore, this research provides knowledge to understand biomarkers in the prior reproduction period.

Exploring the Role of Mediterranean and Westernized Diets and Their Main Nutrients in the Modulation of Oxidative Stress in the Placenta: A Narrative Review

Oxidative stress is a major cellular event that occurs in the placenta, fulfilling critical physiological roles in non-pathological pregnancies. However, exacerbated oxidative stress is a pivotal feature of different obstetric complications, like pre-eclampsia, fetal growth restriction, and other diseases. Compelling evidence supports the relevant role of diet during pregnancy, with pleiotropic consequences for maternal well-being. The present review aims to examine the complex background between oxidative stress and placental development and function in physiological conditions, also intending to understand the relationship between different dietary patterns and the human placenta, particularly how this could influence oxidative stress processes. The effects of Westernized diets (WDs) and high-fat diets (HFDs) rich in ultra-processed foods and different additives are compared with healthy patterns such as a Mediterranean diet (MedDiet) abundant in omega 3 polyunsaturated fatty acids, monounsaturated fatty acids, polyphenols, dietary fiber, and vitamins. Although multiple studies have focused on the role of specific nutrients, mostly in animal models and in vitro, further observational and intervention studies focusing on the placental structure and function in women with different dietary patterns should be conducted to understand the precise influence of diet on this organ.

Events Leading to the Establishment of Pregnancy and Placental Formation: The Need to Fine-Tune the Nomenclature on Pregnancy and Gestation

Today, there is strong and diversified evidence that in humans at least 50% of early embryos do not proceed beyond the pre-implantation period. This evidence comes from clinical investigations, demography, epidemiology, embryology, immunology, and molecular biology. The purpose of this article is to highlight the steps leading to the establishment of pregnancy and placenta formation. These early events document the existence of a clear distinction between embryonic losses during the first two weeks after conception and those occurring during the subsequent months. This review attempts to highlight the nature of the maternal-embryonic dialogue and the major mechanisms active during the pre-implantation period aimed at "selecting" embryos with the ability to proceed to the formation of the placenta and therefore to the completion of pregnancy. This intense molecular cross-talk between the early embryo and the endometrium starts even before the blastocyst reaches the uterine cavity, substantially initiating and conditioning the process of implantation and the formation of the placenta. Today, several factors involved in this dialogue have been identified, although the best-known and overall, the most important, still remains Chorionic Gonadotrophin, indispensable during the first 8 to 10 weeks after fertilization. In addition, there are other substances acting during the first days following fertilization, the Early Pregnancy Factor, believed to be involved in the suppression of the maternal response, thereby allowing the continued viability of the early embryo. The Pre-Implantation Factor, secreted between 2 and 4 days after fertilization. This linear peptide molecule exhibits a self-protective and antitoxic action, is present in maternal blood as early as 7 days after conception, and is absent in the presence of non-viable embryos. The Embryo-Derived Platelet-activating Factor, produced and released by embryos of all mammalian species studied seems to have a role in the ligand-mediated trophic support of the early embryo. The implantation process is also guided by signals from cells in the decidualized endometrium. Various types of cells are involved, among them epithelial, stromal, and trophoblastic, producing a number of cellular molecules, such as cytokines, chemokines, growth factors, and adhesion molecules. Immune cells are also involved, mainly uterine natural killer cells, macrophages, and T cells. In conclusion, events taking place during the first two weeks after fertilization determine whether pregnancy can proceed and therefore whether placenta's formation can proceed. These events represent the scientific basis for a clear distinction between the first two weeks following fertilization and the rest of gestation. For this reason, we propose that a new nomenclature be adopted specifically separating the two periods. In other words, the period from fertilization and birth should be named "gestation", whereas that from the completion of the process of implantation leading to the formation of the placenta, and birth should be named "pregnancy".