The onset of pregnancy is marked by the formation of a zygote, while the culmination of gestation is manifested by the delivery of a fetus. Meanwhile, a successful pregnancy entails a meticulously coordinated sequence of events from embryo implantation to sustained decidualization of the uterus to placental development and childbirth. The decidual reaction, a pivotal process occurring within the endometrium during pregnancy, is finely regulated by sex steroids and cytokines. Notably, fibroblast growth factors (FGFs), particularly FGF2, play a critical role in this physiological cascade. Dysregulated FGF expression may trigger inadequate decidualization, precipitating a spectrum of adverse pregnancy outcomes, including preeclampsia, recurrent implantation failure, and miscarriage. Furthermore, the human decidua, distinct from most mammalian species and similar to great apes, undergoes regular cycles of formation and shedding, independent of the presence of the embryo in the endometrium. This process is also tightly controlled by various FGFs. In this review, we comprehensively compare diverse research decidualization models, delineate the trend of endometrial FGFs during the menstrual cycle, and provide a synopsis of endometrial diseases triggered by FGF dysregulation.
Humans ; Female ; Pregnancy ; Decidua/physiology* ; Animals ; Endometrium/physiology* ; Fibroblast Growth Factors/metabolism* ; Embryo Implantation ; Menstrual Cycle/physiology*

Embryo implantation involves a complex interaction between the embryo and the endometrium of the mother, the study of which faces a variety of problems. The modeling of endometrial epithelial organoids and endometrial assembloids provides a new way to study the process of embryo implantation in vitro. This paper summarized the latest research progress in embryo implantation, the regulation mechanism of endometrial receptivity by estrogen- progesterone coordination and embryo-derived signals, the establishment of endometrial organoids, and the development and application of endometrial assembloids in the research on mother-embryo interaction, providing new strategies for studying the communication between embryo and maternal uterus during implantation.
Endometrium/physiology* ; Organoids/cytology* ; Embryo Implantation/physiology* ; Female ; Animals ; Progesterone/pharmacology* ; Pregnancy ; Estrogens/metabolism* ; Humans

Mosaic embryos contain two or more genetically distinct cell lines, which can be detected by pre-implantation genetic testing for aneuploidy. At present, it has been reported that mosaic embryo transfer can lead to healthy live births. In order to prevent severe adverse pregnancy outcomes, such as implantation failure, abortion, congenital malformation and neonatal death after implantation of mosaic embryos, it is critical to carry out genetic counseling, prenatal diagnosis and pregnancy supervision for mosaic embryo transfer. This article reviews the selection of mosaic embryos, the pregnancy outcomes of mosaic embryo transfer, and the safety of offspring, in order to provide references for the clinical practice of mosaic embryo transfer.
Pregnancy ; Female ; Infant, Newborn ; Humans ; Preimplantation Diagnosis ; Embryo Transfer ; Pregnancy Outcome ; Genetic Testing ; Embryo Implantation/genetics*

The synthesis and decomposition of glycogen adjust the blood glucose dynamically to maintain the energy supply required by the cells. As the only hormone that lowers blood sugar in the body, insulin can promote glycogen synthesis by activating the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway and increasing glucose transporter translocation, and inhibit gluconeogenesis to lower blood glucose. In the endometrium, glycogen metabolism is active, but gluconeogenesis does not occur. The glycogen metabolism in the endometrium is controlled not only by the classical glucose regulating hormones, but also by the ovarian hormones. The functional activities related to implantation of the endometrium during the implantation window require glucose as energy source. A large amount of glucose is used to synthesize glycogen in the endometrium before implantation, which could meet the increased energy demand for embryo implantation. In diabetes, glycogen metabolism in the endometrium is impaired, which frequently leads to implantation failure and early abortion. This article reviews the glycogen metabolism in the endometrium and discusses its role in embryo implantation, which provide new ideas for embryo implantation research and infertility treatment.
Blood Glucose/metabolism* ; Embryo Implantation ; Endometrium ; Female ; Glucose/metabolism* ; Glycogen/metabolism* ; Humans ; Insulin/metabolism* ; Phosphatidylinositol 3-Kinases/metabolism* ; Pregnancy

The transcription factor X-box binding protein-1 (XBP1) plays a key role in unfolded protein reaction. This study was aimed to investigate the expression pattern and regulation of XBP1 in the mouse uterus during early pregnancy. The methods of immunohistochemistry (IHC) and real time quantitative RT-PCR were used to test XBP1 expression in early pregnancy, artificial decidualization, oestrous cycle and hormone-regulated mouse models. The results showed that XBP1 was spatiotemporally expressed in mouse uterus during early pregnancy. The XBP1 protein was mainly detected in the luminal and glandular epithelia on days 1-4 of pregnancy, and was strongly detected in the decidual area on days 5-8 of pregnancy. Similarly, XBP1 expression was also mainly expressed in decidual cells following artificial decidualization. During the oestrous cycle, Xbp1, Xbp1u, and Xbp1s mRNA was predominantly present in proestrus. In the ovariectomized uterus, the expression of XBP1 in luminal and glandular epithelia was up-regulated after estrogen treatment. These results suggest that XBP1 is associated with embryo implantation and decidualization during early pregnancy in mice, and the expression of XBP1 in luminal and glandular epithelia may be regulated by estrogen.
Animals ; Decidua ; Embryo Implantation ; Estrogens ; Female ; Mice ; Pregnancy ; RNA, Messenger/genetics* ; Uterus

Endometrial receptivity has become the main cause of fertilization and pregnancy outcomes in infertile patients,bringing large psychological damage and economic loss to the patients and their family. In recent years,the role of non-coding RNA has increasingly been recognized. The relationship between non-coding RNA and endometrial receptivity is reviewed in this article.
Embryo Implantation ; Endometrium ; physiology ; Female ; Fertilization in Vitro ; Humans ; Pregnancy ; Pregnancy Outcome ; RNA, Untranslated ; genetics

This is a retrospective cohort study comparing blastocyst transfer outcomes following intracytoplasmic sperm injection utilizing epididymal versus testicular sperm for men with obstructive azoospermia. All cases at a single center between 2012 and 2016 were included. Operative approach was selected at the surgeon's discretion and included microepididymal sperm aspiration or testicular sperm extraction. Blastocyst culture was exclusively utilized prior to transfer. The primary outcome was live birth rate. Secondary outcomes included fertilization rate, blastulation rate, euploidy rate, and implantation rate. A mixed effects model was performed. Seventy-six microepididymal sperm aspiration cases and 93 testicular sperm extraction cases were analyzed. The live birth rate was equivalent (48.6% vs 50.5%, P = 0.77). However, on mixed effects model, epididymal sperm resulted in a greater likelihood of fertilization (adjusted OR: 1.37, 95% CI: 1.05-1.81, P = 0.02) and produced a higher blastulation rate (adjusted OR: 1.41, 95% CI: 1.1-1.85, P = 0.01). As a result, the epididymal sperm group had more supernumerary blastocysts available (4.3 vs 3, P < 0.05). The euploidy rate was no different. Pregnancy rates were no different through the first transfer cycle. However, intracytoplasmic sperm injection following microepididymal sperm aspiration resulted in a greater number of usable blastocysts per patient. Thus, the true benefit of epididymal sperm may only be demonstrated via a comparison of cumulative pregnancy rates after multiple transfers from one cohort.
Adult ; Azoospermia ; Embryo Implantation ; Embryo Transfer ; Epididymis/cytology* ; Female ; Humans ; Male ; Pregnancy ; Pregnancy Rate ; Sperm Injections, Intracytoplasmic/methods* ; Sperm Retrieval ; Spermatozoa/cytology* ; Testis/cytology*

Recurrent pregnancy loss (RPL) is a common complication in obstetrics, affecting about 5% of women of childbearing age. An increase in the number of abortions results in escalation in the risk of miscarriage. Although concentrated research has identified numerous causes for RPL, about 50% of them remain unexplained. Pregnancy is a complex process, comprising fertilization, implantation, organ and tissue differentiation, and fetal growth, which is effectively controlled by a number of both maternal and fetal factors. An example is the immune response, in which T cells and natural killer cells participate, and inflammation mediated by tumor necrosis factor or colony-stimulating factor, which hinders embryo implantation. Furthermore, vitamin D affects glucose metabolism and inhibits embryonic development, whereas microRNA has a negative effect on the gene expression of embryo implantation and development. This review examines the causes of RPL from multiple perspectives, and focuses on the numerous factors that may result in RPL.
Abortion, Habitual ; Abortion, Spontaneous ; Colony-Stimulating Factors ; Embryo Implantation ; Embryonic Development ; Female ; Fertilization ; Fetal Development ; Gene Expression ; Glucose ; Humans ; Inflammation ; Killer Cells, Natural ; Metabolism ; MicroRNAs ; Obstetrics ; Pregnancy ; Proteomics ; T-Lymphocytes ; Tumor Necrosis Factor-alpha ; Vitamin D

To investigate whether intrauterine injection of human chorionic gonadotropin (hCG) before the embryo transfer in a frozen-thawed transfer cycle can improve the pregnancy outcome in the patients with repeated implantation failure (RIF).
 Methods: Prospective randomized-controlled trial was adopted. A total of 140 patients, who underwent thawed embryo transplantation and were in line with the diagnosis of RIF, were included. Other patients with some factors, such as uterine malformation, postoperative uterine cavity sticking, tubal effusion, endocrine diseases and endometriosis, were excluded. The patients were randomly divided into 2 groups through the computer random number table: an hCG intrauterine perfusion group and a control group. There was no significant difference in the age, the estradiol level, the number of transplanted embryos, the number of optimal embryos, and the thickness of the endometrium before transplantation between the 2 group (all P>0.05). The hCG+G2 fluid and the G2 fluid were prepared on the day of embryo transfer, and 40 μL of which was injected at an intrauterine site at 3 minutes before embryo transfer in the hCG intrauterine perfusion group and the control group, respectively. The clinical pregnancy rate and implantation rate in the 2 groups were compared.
 Results: The implantation rate and the clinical pregnancy rate in the hCG intrauterine perfusion group were higher than those in the control group (both P<0.05).
 Conclusion: The intrauterine injection of hCG can improve the implantation rate and pregnancy rate in cryopreserved embryo transfer in patients with RIF.
Chorionic Gonadotropin ; Embryo Implantation ; Embryo Transfer ; Female ; Humans ; Pregnancy ; Pregnancy Outcome ; Prospective Studies

OBJECTIVE: To compare human chorionic gonadotropin (HCG)-administered natural cycle with spontaneous ovulatory cycle in patients undergoing frozen-thawed embryo transfer (FTET) in natural cycles. METHODS: In this retrospective cohort study, we analyzed the clinical outcome of a total of 166 consecutive FTET cycles that were performed in either natural cycle controlled by HCG for ovulation triggering (HCG group, n=110) or natural cycle with spontaneous ovulation (control group, n=56) in 166 infertile patients between January 2009 and November 2013. RESULTS: There were no differences in patients' characteristics between the 2 groups. The numbers of oocytes retrieved, mature oocytes, fertilized oocytes, grade I or II embryos and frozen embryos in the previous in vitro fertilization (IVF) cycle in which embryos were frozen were comparable between the HCG and control groups. Significant differences were not also observed between the 2 groups in clinical pregnancy rate (CPR), embryo implantation rate, miscarriage rate, live birth rate and multiple CPR. However, the number of hospital visits for follicular monitoring was significantly fewer in the HCG group than in the control group (P < 0.001). CONCLUSION: Our results demonstrated that HCG administration for ovulation triggering in natural cycle reduces the number of hospital visits for follicular monitoring without any detrimental effect on FTET outcome when compared with spontaneous ovulatory cycles in infertile patients undergoing FTET in natural ovulatory cycles.
Abortion, Spontaneous ; Cardiopulmonary Resuscitation ; Chorion* ; Chorionic Gonadotropin ; Cohort Studies ; Embryo Implantation ; Embryo Transfer* ; Embryonic Structures* ; Female ; Fertilization in Vitro ; Humans* ; Live Birth ; Oocytes ; Ovulation ; Pregnancy ; Pregnancy Rate ; Retrospective Studies ; Zygote*