Embryo implants endometrium-Endometrial receptivity test for implantation failure | ERA

Interactions between embryo and endometrium at implantation are critical for the progression of pregnancy. These reciprocal actions involve exchange of paracrine signals that govern implantation and placentation. However, it remains unknown how these interactions between the conceptus and the endometrium are coordinated at the level of an individual pregnancy. Under the hypothesis that gene expression in endometrium is dependent on gene expression of extraembryonic tissues and genes expressed in extraembryonic tissues are dependent of genes expressed in the endometrium, we performed an integrative analysis of transcriptome profiles of paired extraembryonic tissue and endometria obtained from cattle Bos taurus pregnancies initiated by artificial insemination. The profiles of connectivity revealed distinct coexpression patterns of extraembryonic tissues with caruncular and intercaruncular areas of the endometrium.

Embryo implants endometrium

Embryo implants endometrium

Embryo implants endometrium

Embryo implants endometrium

Embryo implants endometrium

Many women undergoing IVF are unable to get pregnant, even after transferring good quality embryos. Paulson RJ. Cell Cycle6 Explore Implantw Development. Sunderland, MA: Sinauer, Activation of the protein kinase A pathway in human endometrial stromal cells Embryo implants endometrium sequential categorical gene regulation. Hypothalamic—pituitary—gonadal axis Hypothalamic—pituitary—prolactin axis Andrology Hormone. Human chorionic gonadotropin is an autocrine growth factor for the blastocyst.

Nude bollywood females. Other services

Leave me a comment in the box endmoetrium. Although progesterone and estrogen are the Embryo implants endometrium modulators of endometrial maturation, Embryo implants endometrium roles in this process are complex and sophisticated Punyadeera et al. A critical analysis of the accuracy, reproducibility, and clinical utility of histologic endometrial dating in fertile women. Implantation itself is governed by an array of endocrine, paracrine and autocrine modulators, of embryonic and maternal origin. Luminal and glandular endometrial epithelium express Free indian sex videos clips stories differentially throughout the menstrual cycle: implications for implantation, contraception, and infertility. Elsevier Health Sciences, Doctors also endometriu for high concentrations of integrins when they look for areas of uteruses receptive to implantation in assisted reproductive therapy ARTand they use the lack of such concentrations to identify women who may be endometruum. The reception-ready phase of the endometrium of the uterus is usually termed the "implantation window" and lasts about 4 days. Citing articles via Web of Science Ultimately, the aim is to Embryo implants endometrium these tools to increase implantation in artificial cycles and consequently improve implante rates. If the zygote implants in any area besides the uterusthe result is an ectopic pregnancy.

It is by this adhesion that the embryo receives oxygen and nutrients from the mother to be able to grow.

  • For this process to work, certain conditions must be met to increase the success of implantation and overcome implantation difficulties.
  • At ovulation the egg is released from the dominate ovarian follicle from the wall of the ovary and 'grabbed' up by the fimbria and pulled into the fallopian tube.

It is by this adhesion that the embryo receives oxygen and nutrients from the mother to be able to grow. The reception-ready phase of the endometrium of the uterus is usually termed the "implantation window" and lasts about 4 days. The implantation window occurs around 6 days after the peak in luteinizing hormone levels. With some disparity between sources, it has been stated to occur from 7 days after ovulation until 9 days after ovulation, [2] or days postovulation.

The implantation window is characterized by changes to the endometrium cells, which aid in the absorption of the uterine fluid.

These changes are collectively known as the plasma membrane transformation and bring the blastocyst nearer to the endometrium and immobilize it. To enable implantation, the uterus goes through changes in order to be able to receive the conceptus. The endometrium increases thickness, becomes vascularized and its glands grow to be tortuous and boosted in their secretions.

These changes reach their maximum about 7 days after ovulation. This happens about 9 to 10 days after ovulation. The uterine glands, on the other hand, decrease in activity and degenerate around 8 to 9 days [6] after ovulation in absence of pregnancy.

The decidual cells originate from the stromal cells that are always present in the endometrium. However, the decidual cells make up a new layer, the decidua. The rest of the endometrium, in addition, expresses differences between the luminal and the basal sides. The luminal cells form the zona compacta of the endometrium, in contrast to the basalolateral zona spongiosa , which consists of the rather spongy stromal cells.

Decidualization succeeds predecidualization if pregnancy occurs. This is an expansion of it, further developing the uterine glands, the zona compacta and the epithelium of decidual cells lining it.

The decidual cells become filled with lipids and glycogen and take the polyhedral shape characteristic for decidual cells. It is likely that the blastocyst itself makes the main contribution to this additional growing and sustaining of the decidua.

An indication of this is that decidualization occurs at a higher degree in conception cycles than in nonconception cycles. After implantation the decidua remains, at least through the first trimester. Its function as a surrounding tissue is replaced by the definitive placenta. However, some elements of the decidualization remain throughout pregnancy. The compacta and spongiosa layers are still observable beneath the decidua in pregnancy. The glands of the spongiosa layer continue to secrete during the first trimester, when they degenerate.

However, before that disappearance, some glands secrete unequally much. This phenomenon of hypersecretion is called the Arias-Stella phenomenon , [6] after the pathologist Javier Arias-Stella.

Pinopodes are small, finger-like protrusions from the endometrium. They appear between day 19 and day 21 [6] of gestational age. This corresponds to a fertilization age of approximately five to seven days, which corresponds well with the time of implantation. They only persist for two to three days. Pinopodes endocytose uterine fluid and macromolecules in it. By doing so, the volume of the uterus decreases, taking the walls closer to the embryoblast floating in it.

Thus, the period of active pinocytes might also limit the implantation window. Not only the lining of the uterus transforms, but in addition, the secretion from its epithelial glands changes. This change is induced by increased levels of progesterone from the corpus luteum. The target of the secretions is the embryoblast, and has several functions on it.

The embryoblast spends approximately 72 hours [6] in the uterine cavity before implanting. In that time, it cannot receive nourishment directly from the blood of the mother, and must rely on secreted nutrients into the uterine cavity, e.

In addition to nourishment, the endometrium secretes several steroid -dependent proteins, [6] important for growth and implantation. Cholesterol [6] and steroids [6] are also secreted. Implantation is further facilitated by synthesis of matrix substances, adhesion molecules and surface receptors for the matrix substances. To be able to perform implantation, the blastocyst first needs to get rid of its zona pellucida.

This process can be called "hatching". Lytic factors in the uterine cavity, as well as factors from the blastocyst itself are essential for this process. Mechanisms in the latter are indicated by that the zona pellucida remains intact if an unfertilized egg is placed in the uterus under the same conditions. Plasminogen , the plasmin precursor, is found in the uterine cavity, and blastocyst factors contribute to its conversion to active plasmin.

This hypothesis is supported by lytic effects in vitro by plasmin. The very first, albeit loose, connection between the blastocyst and the endometrium is called the apposition. Nevertheless, the apposition on the blastocyst is not dependent on if it is on the same side of the blastocyst as the inner cell mass.

Rather, the inner cell mass rotates inside the trophoblast to align to the apposition. The identity of the molecules on the trophoblast and the endometrial epithelia that mediate the initial interaction between the two remain unidentified. However, a number of research groups have proposed that MUC1 , a member of the Mucin family of glycosylated proteins, is involved. The blastocyst signals to the endometrium to adapt further to its presence, e.

This, in turn, dislodges the decidual cells from their connection to the underlying basal lamina , which enables the blastocyst to perform the succeeding invasion.

This communication is conveyed by receptor - ligand -interactions, both integrin-matrix and proteoglycan ones. Another ligand-receptor system involved in adhesion is proteoglycan receptors, found on the surface of the decidua of the uterus. Their counterparts, the proteoglycans, are found around the trophoblast cells of the blastocyst. This ligand-receptor system also is present just at the implantation window. The protrusions of trophoblast cells that adhere into the endometrium continue to proliferate and penetrate into the endometrium.

As these trophoblast cells penetrate, they differentiate to become a new type of cells, syncytiotrophoblast. The prefix syn- refers to the transformation that occurs as the boundaries between these cells disappear to form a single mass of many cell nuclei a syncytium. The rest of the trophoblasts, surrounding the inner cell mass, are hereafter called cytotrophoblasts. Invasion continues with the syncytiotrophoblasts reaching the basal membrane beneath the decidual cells, penetrating it and further invading into the uterine stroma.

Finally, the whole embryo is embedded in the endometrium. This is the initiation of forming the placenta. The blastocyst secretes factors for a multitude of purposes during invasion. It secretes several autocrine factors, targeting itself and stimulating it to further invade the endometrium. Human chorionic gonadotropin is an autocrine growth factor for the blastocyst.

The syncytiotrophoblasts dislodges decidual cells in their way, both by degradation of cell adhesion molecules linking the decidual cells together as well as degradation of the extracellular matrix between them. Cell adhesion molecules are degraded by syncytiotrophoblast secretion of Tumor necrosis factor-alpha. This inhibits the expression of cadherins and beta-catenin. Inhibited expression of these molecules thus loosens the connection between decidual cells, permitting the syncytotrophoblasts and the whole embryo with them to invade into the endometrium.

The extracellular matrix is degraded by serine endopeptidases and metalloproteinases. Examples of such metalloproteinases are collagenases , gelatinases and stromelysins. The embryo differs from the cells of the mother, and would be rejected as a parasite by the immune system of the mother if it didn't secrete immunosuppressive agents.

Factors from the blastocyst also trigger the final formation of decidual cells into their proper form. In contrast, some decidual cells in the proximity of the blastocyst degenerate, providing nutrients for it.

Human chorionic gonadotropin hCG not only acts as an immunosuppressive, [6] but also "notifies" the mother's body that she is pregnant , preventing menstruation by sustaining the function of the corpus luteum. Implantation failure is considered to be caused by inadequate uterine receptivity in two-thirds of cases, and by problems with the embryo itself in the other third. Inadequate uterine receptivity may be caused by abnormal cytokine and hormonal signaling as well as epigenetic alterations.

Therefore, pregnancy rates can be improved by optimizing endometrial receptivity for implantation. Luteal support is the administration of medication, generally progestins , for the purpose of increasing the success rate of implantation and early embryogenesis , thereby complementing the function of the corpus luteum.

From Wikipedia, the free encyclopedia. Main article: Pinopod. Main article: Zona hatching. New England Journal of Medicine. Fertility and Sterility. Elnashar, Gamal I. Endometrial receptivity. Human Embryology. Online course in embryology for medicine students developed by the universities of Fribourg, Lausanne and Bern Switzerland with the support of the Swiss Virtual Campus.

Retrieved 6 December Oxford : Elsevier. PLOS One. Human Reproduction Update. Human embryogenesis in the first three weeks. Hypoblast Epiblast. Surface ectoderm Neuroectoderm Somatopleuric mesenchyme Neurulation Neural crest.

The expression of adhesion molecules, such as integrins, selectins, cadherins, and the immunoglobulin superfamily, is also thought to be involved in the development of a receptive state. Implantation is further facilitated by synthesis of matrix substances, adhesion molecules and surface receptors for the matrix substances. However, androgen receptors are present on stromal and epithelial cells in the endometrium, and both androstenedione and testosterone induce changes in endometrial function that may be important during implantation Kodaman and Taylor, Citing articles via Web of Science Human chorionic gonadotropin is an autocrine growth factor for the blastocyst.

Embryo implants endometrium

Embryo implants endometrium. Possible Pregnancy Implantation Symptoms and Signs

The implantation window is characterized by changes to the endometrium cells, which aid in the absorption of the uterine fluid. These changes are collectively known as the plasma membrane transformation and bring the blastocyst nearer to the endometrium and immobilize it. To enable implantation, the uterus goes through changes in order to be able to receive the conceptus. The endometrium increases thickness, becomes vascularized and its glands grow to be tortuous and boosted in their secretions.

These changes reach their maximum about 7 days after ovulation. This happens about 9 to 10 days after ovulation. The uterine glands, on the other hand, decrease in activity and degenerate around 8 to 9 days [6] after ovulation in absence of pregnancy. The decidual cells originate from the stromal cells that are always present in the endometrium.

However, the decidual cells make up a new layer, the decidua. The rest of the endometrium, in addition, expresses differences between the luminal and the basal sides. The luminal cells form the zona compacta of the endometrium, in contrast to the basalolateral zona spongiosa , which consists of the rather spongy stromal cells. Decidualization succeeds predecidualization if pregnancy occurs. This is an expansion of it, further developing the uterine glands, the zona compacta and the epithelium of decidual cells lining it.

The decidual cells become filled with lipids and glycogen and take the polyhedral shape characteristic for decidual cells. It is likely that the blastocyst itself makes the main contribution to this additional growing and sustaining of the decidua.

An indication of this is that decidualization occurs at a higher degree in conception cycles than in nonconception cycles. After implantation the decidua remains, at least through the first trimester. Its function as a surrounding tissue is replaced by the definitive placenta.

However, some elements of the decidualization remain throughout pregnancy. The compacta and spongiosa layers are still observable beneath the decidua in pregnancy.

The glands of the spongiosa layer continue to secrete during the first trimester, when they degenerate. However, before that disappearance, some glands secrete unequally much. This phenomenon of hypersecretion is called the Arias-Stella phenomenon , [6] after the pathologist Javier Arias-Stella.

Pinopodes are small, finger-like protrusions from the endometrium. They appear between day 19 and day 21 [6] of gestational age. This corresponds to a fertilization age of approximately five to seven days, which corresponds well with the time of implantation.

They only persist for two to three days. Pinopodes endocytose uterine fluid and macromolecules in it. By doing so, the volume of the uterus decreases, taking the walls closer to the embryoblast floating in it. Thus, the period of active pinocytes might also limit the implantation window. Not only the lining of the uterus transforms, but in addition, the secretion from its epithelial glands changes.

This change is induced by increased levels of progesterone from the corpus luteum. The target of the secretions is the embryoblast, and has several functions on it.

The embryoblast spends approximately 72 hours [6] in the uterine cavity before implanting. In that time, it cannot receive nourishment directly from the blood of the mother, and must rely on secreted nutrients into the uterine cavity, e. In addition to nourishment, the endometrium secretes several steroid -dependent proteins, [6] important for growth and implantation.

Cholesterol [6] and steroids [6] are also secreted. Implantation is further facilitated by synthesis of matrix substances, adhesion molecules and surface receptors for the matrix substances. To be able to perform implantation, the blastocyst first needs to get rid of its zona pellucida. This process can be called "hatching". Lytic factors in the uterine cavity, as well as factors from the blastocyst itself are essential for this process.

Mechanisms in the latter are indicated by that the zona pellucida remains intact if an unfertilized egg is placed in the uterus under the same conditions.

Plasminogen , the plasmin precursor, is found in the uterine cavity, and blastocyst factors contribute to its conversion to active plasmin. This hypothesis is supported by lytic effects in vitro by plasmin. The very first, albeit loose, connection between the blastocyst and the endometrium is called the apposition.

Nevertheless, the apposition on the blastocyst is not dependent on if it is on the same side of the blastocyst as the inner cell mass. Rather, the inner cell mass rotates inside the trophoblast to align to the apposition. The identity of the molecules on the trophoblast and the endometrial epithelia that mediate the initial interaction between the two remain unidentified. However, a number of research groups have proposed that MUC1 , a member of the Mucin family of glycosylated proteins, is involved.

The blastocyst signals to the endometrium to adapt further to its presence, e. This, in turn, dislodges the decidual cells from their connection to the underlying basal lamina , which enables the blastocyst to perform the succeeding invasion. This communication is conveyed by receptor - ligand -interactions, both integrin-matrix and proteoglycan ones.

Another ligand-receptor system involved in adhesion is proteoglycan receptors, found on the surface of the decidua of the uterus. Their counterparts, the proteoglycans, are found around the trophoblast cells of the blastocyst.

This ligand-receptor system also is present just at the implantation window. The protrusions of trophoblast cells that adhere into the endometrium continue to proliferate and penetrate into the endometrium. As these trophoblast cells penetrate, they differentiate to become a new type of cells, syncytiotrophoblast. The prefix syn- refers to the transformation that occurs as the boundaries between these cells disappear to form a single mass of many cell nuclei a syncytium. The rest of the trophoblasts, surrounding the inner cell mass, are hereafter called cytotrophoblasts.

Invasion continues with the syncytiotrophoblasts reaching the basal membrane beneath the decidual cells, penetrating it and further invading into the uterine stroma. Finally, the whole embryo is embedded in the endometrium. This is the initiation of forming the placenta.

The blastocyst secretes factors for a multitude of purposes during invasion. It secretes several autocrine factors, targeting itself and stimulating it to further invade the endometrium. Human chorionic gonadotropin is an autocrine growth factor for the blastocyst.

The syncytiotrophoblasts dislodges decidual cells in their way, both by degradation of cell adhesion molecules linking the decidual cells together as well as degradation of the extracellular matrix between them. Tools are now available that enable the selection of high-quality embryos or assessment of endometrial status. However, despite these advances, pregnancy rates are still relatively low and have not increased significantly in the last decade Nygren and Andersen, ; Andersen et al.

This suggests that implantation rates in stimulated cycles remain suboptimal. Other factors, which are yet to be identified, must play a role. Historically, both endometrial receptivity and embryo quality have been judged using morphological assessments, and the search for predictors of implantation has focused primarily on the analysis of single markers.

This strategy may be particularly relevant in the field of implantation because numerous factors are involved, many of these have multiple functions, and there is potentially a large amount of redundancy.

The aim of this review is to outline the current understanding of implantation in humans and to describe and critique the tools currently available for the study of the human preimplantation embryo, the receptivity of the endometrium and the embryo—uterine dialogue. In addition, this review will identify key areas in implantation research and methodology where efforts need to be focused in the future. Prior to implantation, the blastocyst shows evidence of polarity, assuming a particular orientation as it approaches the endometrium.

Once the blastocyst is oriented correctly apposition , the zona pellucida is shed. Finally, the blastocyst penetrates the epithelial layer and invades the stroma invasion. Successful implantation requires the appropriately timed arrival of a viable blastocyst into a receptive endometrium.

The importance of endometrial environment is highlighted by the observation that high-quality embryos transferred into women involved as embryo recipients in a surrogacy procedure have a higher probability of implanting than if they are transferred back into the donor women Check et al.

Poor embryo quality has also been identified as a major cause of implantation failure Urman et al. It is clear that to improve implantation rates in stimulated cycles, it is important to find ways to pinpoint the window of implantation, ensure that the best embryo is selected and synchronize embryo transfer with the time of optimal endometrial receptivity.

Importantly, ways of evaluating and enhancing endometrial receptivity and embryo quality without disrupting the delicate process of implantation itself must be identified. This dialogue enables synchronous development of the oocyte and maturation of the endometrium, followed by embryo orientation, apposition, adhesion and endometrial invasion by the blastocyst Enders et al.

By understanding the activity and function of the hormones and factors involved in this dialogue, it may be possible to use them as predictors of endometrial receptivity or embryo quality to maximize implantation rates in hormonally stimulated ART cycles.

The majority of spontaneous human conceptions fail to complete implantation and to achieve ongoing pregnancy. The proportion of human conceptions that fail to implant remains uncertain, as data are limited. The frequency of embryonic genetic abnormality increases with maternal age Hassold et al. Therefore, genetic abnormalities are thought to be a major factor contributing to implantation failure in ART. Patients undergoing ART procedures often hold unrealistically high expectations of achieving pregnancy Peddie et al.

The endometrium is a multilayered, dynamic organ overlaying the myometrium and comprises a functional layer and a basal layer. Each month, cells in the functional layer are separated from the basal layer during menstruation. The basal layer is attached to the myometrium and remains intact during menstruation, serving as a base for endometrial regeneration.

The endometrium is composed of several different cell types, including luminal and glandular epithelial cells, stroma with stromal fibroblastic cells, immunocompetent cells and blood vessels.

The numbers, activity, structure and function of these cells change throughout the menstrual cycle and change again during pregnancy. In the early s, Noyes and co-workers Noyes et al.

By associating histological changes with natural changes in basal body temperature, they were able to link distinct histological patterns to particular time points during the menstrual cycle.

The criteria for endometrial dating that resulted from this work have since remained the gold standard approach for evaluating endometrial responsiveness and detecting endometrial abnormalities. Endometrial biopsy is known to disrupt normal anatomical layering. Biopsies may contain different parts of the endometrial layers, low uterine segment fragments and variable amounts of glands or stroma.

Nevertheless, compared with other biopsy techniques, analysis of samples using the Noyes method generally allows evaluation of the cellular architecture. Strengths and limitations of morphological and immunohistochemistry assessments of endometrial receptivity.

As well as these benefits, a number of weaknesses in Noyes' approach have been identified. Biopsies can only provide a snapshot of the real situation in the endometrium, and sample bias is unavoidable because it is not applicable to take large numbers of samples.

Variability is also introduced because of the differences between women and the differences between cycles in the same woman Murray et al. The issue of timing based on endometrial dating is critical Fig. During the 2 days following ovulation, the morphological features of the endometrium do not change significantly. Therefore, an error of 2 days is introduced into endometrial dating for biopsies taken during this period.

A similar situation is evident for biopsies taken during the mid-luteal phase, where there is lack of positive morphology criteria for a period of 4—5 days stromal oedema is the only feature that changes significantly during this period.

Graph illustrating the Noyes method of endometrial dating, which highlights the uncertainty in timing introduced during the post-ovulatory period, the mid-luteal phase and by measuring the LH surge.

The distribution over time of many observed changes is too diffuse to allow precise endometrial dating, for example 2 days of the post-ovulatory period and 4—5 days in the mid-luteal phase. Using the luteinizing hormone LH surge to predict ovulation is one approach that has been investigated, although there would still remain a degree of uncertainty in timing, as the LH surge occurs over a period of 30 h Acosta et al.

Electron microscopy allows the examination of endometrial ultrastructures present during the implantation window, such as pinopodes and nucleolar channels, which may prove useful markers of endometrial receptivity Bentin-Ley et al. Methods that associate morphology and function e. Unfortunately, immunohistochemistry suffers from the same problems as morphological assessments.

In the future, laser capture microdissection may be coupled with gene expression analysis, providing another useful tool that could be used to link endometrial morphology and function Yanaihara et al. Another key consideration when using endometrial dating is that it disregards the status of the embryo. Ensuring the endometrium is receptive is of little use if a poor-quality embryo is introduced. Therefore, to ensure optimal conditions for implantation, endometrial dating should not be used in isolation, but should be combined with other techniques that provide information about embryo quality.

Progesterone and estrogen are the dominant hormonal modulators of endometrial development. Ovarian estrogen and progesterone condition the uterus for implantation, and knowledge about the precise temporal action of these hormones within the menstrual cycle has allowed the development of hormone-based contraception. Both the epithelial and stromal compartments express progesterone and estrogen receptors, and the response depends on the levels of these receptors as well as on the concentration of the hormones themselves.

The interactions of progesterone and estrogen with estrogen receptors ER during endometrial development are illustrated in Fig. It is apparent that the appropriate cyclical pattern of receptor expression is crucial for achieving endometrial receptivity and successful implantation Lessey, ; Ma et al. The roles of progesterone and estrogen E 2 ; E 3 , estriol and estrogen receptors ER during endometrial development.

Changes in the expression of progesterone receptors PRA, PRB in glandular epithelial cells and stromal cells during the different phases of the menstrual cycle. Adapted with permission from Mote et al.

Although progesterone and estrogen are the key modulators of endometrial maturation, their roles in this process are complex and sophisticated Punyadeera et al. Hormonal activity depends on not only the levels of progesterone, estrogen and their receptors, but also on the rates of progesterone and estrogen metabolism e. The activities of progesterone and estrogen are also influenced by the effects of co-activators and repressors Punyadeera et al.

In addition to progesterone and estrogen, a number of other endocrinological factors are known to mediate endometrial function Kodaman and Taylor, The effects of androgens are often overlooked in the female reproductive cycle.

However, androgen receptors are present on stromal and epithelial cells in the endometrium, and both androstenedione and testosterone induce changes in endometrial function that may be important during implantation Kodaman and Taylor, Endometrial factors are critical mediators of all phases of the implantation process Fig.

Once the embryo reaches the uterus, the first cells it encounters are the epithelial cells of the endometrium. These cells secrete a range of factors into the uterine lumen, which may affect embryonic attachment as well as further development of the early placenta and embryo.

Adapted with permission from Dimitriadis et al. In humans, one factor that has attracted particular interest is leukaemia-inhibitory factor LIF , which is an interleukin IL -6 cytokine expressed in endometrial epithelial cells at the appropriate time for which receptors are present on preimplantation embryos.

Studies in mice demonstrate that LIF plays a role in implantation and may also promote embryonic development.

Observational studies in humans are suggestive of a possible role for LIF in humans Robb et al. Indeed, infertility in some women has been associated with the dysregulation of LIF, and also of IL, which is produced in the same manner in the endometrial glands during the receptive phase Dimitriadis et al. With the increasing trend towards single embryo transfer in ART Vilska et al. Preimplantation genetic diagnosis PGD was initially developed as a preconception test for couples carrying genetic disorders who were at risk of having a child affected by the disorder Thornhill et al.

Chromosomal analysis of human gametes and embryos has revealed that chromosome aberrations occur at high frequency in the early preimplantation embryo. Another key issue in ART protocols that is still under debate is the timing of embryo transfer.

Whereas in an unselected patient population a clinical benefit of day-5 transfer blastocyst transfer with respect to live-birth rate and multiple-pregnancy rate has not been shown Blake et al.

Blastocyst transfer gives the option to select the morphologically best embryo, whereas it has also been indicated that good-quality blastocysts have a decreased incidence of aneuploidy Fig. Figure reproduced with permission from Staessen et al. Failure of the blastocyst to release from the zona pellucida has been identified as a potential cause of implantation failure in assisted cycles, particularly in older women Seif et al.

A potential solution to this is artificial disruption of the zona pellucida or assisted hatching. A systematic review of studies investigating the effects of this technique on conception found that assisted hatching significantly improved pregnancy rates, but had no effect on live-birth rates or spontaneous abortion rates, and multiple-pregnancy rates were significantly increased Seif et al.

Unfortunately, there were insufficient data for this analysis to investigate the impact of assisted hatching on a number of other important outcomes, such as monozygotic twinning, embryo damage, congenital and chromosomal abnormalities and in vitro blastocyst development.

When optimizing ART procedures to mimic nature as closely as possible, it is important to remember that controlled ovarian stimulation itself interrupts natural physiological processes and is likely to alter key parameters such as the rate of embryonic development and the extent and timing of endometrial receptivity. Artificial stimulation affects the levels of progesterone and estrogen, the ratio between these two hormones and endometrial expression of their receptors Beckers et al.

There is evidence that supraphysiological steroid levels impair the luteal phase, and this is true, even when stimulation is started in the late follicular phase Bourgain et al. Therefore, if the luteal phase is not supplemented, premature luteolysis can occur and pregnancy may not be achieved Beckers et al.

In ART cycles, the aim is to produce multiple mature follicles, which leads to elevated levels of progesterone and estrogen compared with natural cycles, and this can induce changes in the endometrium Bourgain and Devroey, that can be detected using standard histological techniques Garcia et al. To overcome some of the effects potentially associated with hormonal stimulation, various modified stimulation protocols have been investigated.

The implantation process itself has never been observed directly in vivo in humans Lee and DeMayo, However, studies in animals, primarily rodents, sheep and primates, have provided clues about the hormonal and morphological changes that might occur in women prior to and during implantation Lee and DeMayo, Conversely, macaques and humans have similar mechanisms for trophoblast invasion and, therefore, macaques are a suitable model for studying the later phases of implantation Lee and DeMayo, However, the mechanisms of implantation in mice and humans are quite distinct.

During implantation in mice, the luminal epithelium forms an invagination that surrounds the trophoblast eccentric mechanism and is subsequently shed by apoptosis, whereas in humans, the trophoblast invades the stroma by penetrating the luminal epithelium interstitial mechanism Wimsatt, Collectively, these data question an essential role for LIF in human implantation and are cause for reflection as to the translatability of animal studies to human biology. This issue of translatability has important implications for future research, as rodent models are best suited for testing the functional role of genes and proteins.

To address this need, a number of in vitro models using human cell culture systems have been developed to study various aspects of embryo—endometrial interaction. Bentin-Ley et al. Using this model, they demonstrated that human blastocysts attach preferentially to pinopode-presenting areas on the endometrial surface Bentin-Ley et al. Another group cultured a complete endometrial biopsy of the upper functional layer of the endometrium onto collagen gel Landgren et al.

Simon et al. In the apposition model, embryos obtained after ovarian superovulation and insemination IVF or intracytoplasmic sperm injection were co-cultured with luteal phase endometrial epithelial cells. For the adhesion model, a 3D culture was prepared, comprising epithelial and stromal cells cultured from endometrial biopsies.

These models have provided information about the embryonic regulation of endometrial epithelial molecules such as anti-adhesion molecules Meseguer et al. An in vitro model has also been developed to study the process of blastocyst invasion Carver et al.

Carver et al. Advances in biotechnology have lead to the development of new techniques that allow the examination of changes in the endometrium and embryo at the molecular level. DNA microarrays enable analysis of the simultaneous expression of thousands of genes in a single sample. These genomic and proteomic techniques have been used to study changes occurring throughout the cycle, examine the impact of artificial stimulation and determine the patterns of gene expression in different cell types.

The expression of many endometrial genes has been shown to change over the course of the menstrual cycle Ponnampalam et al.

However, some of these expression patterns do not appear to associate with histopathological changes occurring in the endometrium Ponnampalam et al. To date, five studies have examined changes in endometrial gene expression during the receptive phase and all have reported genes that are strongly up- or down-regulated when the endometrium is receptive Carson et al. One striking observation is that only a single gene osteopontin was differentially expressed up-regulated in all five of these studies Carson et al.

This finding highlights the need for standardization of methodology if meaningful conclusions are to be made from genomic and proteomic studies. Microarray studies comparing natural and stimulated cycles indicate that controlled ovarian stimulation has a profound effect on endometrial gene expression during the window of implantation 7 days after the LH surge compared with 2 days; Fig.

Over genes were differentially expressed in stimulated cycles Horcajadas et al. Studies have also examined gene expression changes in human endometrial cells in vitro during decidualization Popovici et al.

Principle component analyses PCA of endometrial gene expression showing clustering of samples from A 2 versus 7 days after the LH surge or B natural versus stimulated cycles. Adapted with permission from Riesewijk et al. Laser capture microdissection coupled with gene expression analysis enables accurate comparison of gene expression patterns between different cell types from the same tissue.

To date, one study has used this technique to examine differences in normal human endometrial tissues from the secretory phase Yanaihara et al. A total of 28 genes were found to be differentially expressed in epithelial and stromal cells, and a number of these genes have known immunological functions Yanaihara et al. As well as array technologies being used to study gene expression, methods are also being developed to study proteomic changes occurring during implantation.

Endometrial secretion aspiration is one such approach and enables the measurement of protein changes in the uterine lumen during treatment cycles van der Gaast et al. As well as studying the molecular changes occurring in the endometrium, it is equally important to conduct molecular studies on oocytes and embryos, but unfortunately these have been few Neilson et al.

Two of these studies have investigated differential gene or protein expression in human embryos Dobson et al. Dobson et al. Katz-Jaffe et al. However, when assessing oocytes and embryos, much smaller amounts of material can be obtained compared with endometrial samples. The fewer cells that are removed from the embryo or blastocyst , the less disruption is likely to be caused. Therefore, highly accurate methods of amplification and detection are required.

Investigators at Serono International SA Geneva, Switzerland have begun to develop tools and a strategy to enable molecular-based embryo selection Fig. Using this approach, RNA amplification from a single blastomere provided sufficient amplified RNA for microarray analysis.

The expression of over genes was detected in day 3 human embryos and enzyme-linked immunosorbent assay ELISA is in progress to confirm the expression of these genes.

Diedrich, B. Fauser, P. Devroey, G. Despite many advances in assisted reproductive technologies ART , implantation rates are still low. The process of implantation requires a reciprocal interaction between blastocyst and endometrium, culminating in a small window of opportunity during which implantation can occur.

This interaction involves the embryo, with its inherent molecular programme of cell growth and differentiation, and the temporal differentiation of endometrial cells to attain uterine receptivity. Implantation itself is governed by an array of endocrine, paracrine and autocrine modulators, of embryonic and maternal origin.

Therefore a better comprehension of implantation, and the relative importance of the factors involved, is warranted.

Continuing refinements to ART protocols, such as optimizing ovarian stimulation regimens, the timing of human chorionic gonadotrophin injection, or the timing of embryo transfer, should help to increase implantation rates further. The techniques used in assisted reproductive technologies ART have advanced considerably since the first in vitro fertilization IVF birth in Tools are now available that enable the selection of high-quality embryos or assessment of endometrial status.

However, despite these advances, pregnancy rates are still relatively low and have not increased significantly in the last decade Nygren and Andersen, ; Andersen et al. This suggests that implantation rates in stimulated cycles remain suboptimal.

Other factors, which are yet to be identified, must play a role. Historically, both endometrial receptivity and embryo quality have been judged using morphological assessments, and the search for predictors of implantation has focused primarily on the analysis of single markers.

This strategy may be particularly relevant in the field of implantation because numerous factors are involved, many of these have multiple functions, and there is potentially a large amount of redundancy.

The aim of this review is to outline the current understanding of implantation in humans and to describe and critique the tools currently available for the study of the human preimplantation embryo, the receptivity of the endometrium and the embryo—uterine dialogue. In addition, this review will identify key areas in implantation research and methodology where efforts need to be focused in the future.

Prior to implantation, the blastocyst shows evidence of polarity, assuming a particular orientation as it approaches the endometrium. Once the blastocyst is oriented correctly apposition , the zona pellucida is shed. Finally, the blastocyst penetrates the epithelial layer and invades the stroma invasion. Successful implantation requires the appropriately timed arrival of a viable blastocyst into a receptive endometrium.

The importance of endometrial environment is highlighted by the observation that high-quality embryos transferred into women involved as embryo recipients in a surrogacy procedure have a higher probability of implanting than if they are transferred back into the donor women Check et al.

Poor embryo quality has also been identified as a major cause of implantation failure Urman et al. It is clear that to improve implantation rates in stimulated cycles, it is important to find ways to pinpoint the window of implantation, ensure that the best embryo is selected and synchronize embryo transfer with the time of optimal endometrial receptivity. Importantly, ways of evaluating and enhancing endometrial receptivity and embryo quality without disrupting the delicate process of implantation itself must be identified.

This dialogue enables synchronous development of the oocyte and maturation of the endometrium, followed by embryo orientation, apposition, adhesion and endometrial invasion by the blastocyst Enders et al. By understanding the activity and function of the hormones and factors involved in this dialogue, it may be possible to use them as predictors of endometrial receptivity or embryo quality to maximize implantation rates in hormonally stimulated ART cycles. The majority of spontaneous human conceptions fail to complete implantation and to achieve ongoing pregnancy.

The proportion of human conceptions that fail to implant remains uncertain, as data are limited. The frequency of embryonic genetic abnormality increases with maternal age Hassold et al.

Therefore, genetic abnormalities are thought to be a major factor contributing to implantation failure in ART. Patients undergoing ART procedures often hold unrealistically high expectations of achieving pregnancy Peddie et al. The endometrium is a multilayered, dynamic organ overlaying the myometrium and comprises a functional layer and a basal layer. Each month, cells in the functional layer are separated from the basal layer during menstruation. The basal layer is attached to the myometrium and remains intact during menstruation, serving as a base for endometrial regeneration.

The endometrium is composed of several different cell types, including luminal and glandular epithelial cells, stroma with stromal fibroblastic cells, immunocompetent cells and blood vessels. The numbers, activity, structure and function of these cells change throughout the menstrual cycle and change again during pregnancy.

In the early s, Noyes and co-workers Noyes et al. By associating histological changes with natural changes in basal body temperature, they were able to link distinct histological patterns to particular time points during the menstrual cycle. The criteria for endometrial dating that resulted from this work have since remained the gold standard approach for evaluating endometrial responsiveness and detecting endometrial abnormalities.

Endometrial biopsy is known to disrupt normal anatomical layering. Biopsies may contain different parts of the endometrial layers, low uterine segment fragments and variable amounts of glands or stroma. Nevertheless, compared with other biopsy techniques, analysis of samples using the Noyes method generally allows evaluation of the cellular architecture. Strengths and limitations of morphological and immunohistochemistry assessments of endometrial receptivity.

As well as these benefits, a number of weaknesses in Noyes' approach have been identified. Biopsies can only provide a snapshot of the real situation in the endometrium, and sample bias is unavoidable because it is not applicable to take large numbers of samples. Variability is also introduced because of the differences between women and the differences between cycles in the same woman Murray et al.

The issue of timing based on endometrial dating is critical Fig. During the 2 days following ovulation, the morphological features of the endometrium do not change significantly. Therefore, an error of 2 days is introduced into endometrial dating for biopsies taken during this period. A similar situation is evident for biopsies taken during the mid-luteal phase, where there is lack of positive morphology criteria for a period of 4—5 days stromal oedema is the only feature that changes significantly during this period.

Graph illustrating the Noyes method of endometrial dating, which highlights the uncertainty in timing introduced during the post-ovulatory period, the mid-luteal phase and by measuring the LH surge. The distribution over time of many observed changes is too diffuse to allow precise endometrial dating, for example 2 days of the post-ovulatory period and 4—5 days in the mid-luteal phase.

Using the luteinizing hormone LH surge to predict ovulation is one approach that has been investigated, although there would still remain a degree of uncertainty in timing, as the LH surge occurs over a period of 30 h Acosta et al.

Electron microscopy allows the examination of endometrial ultrastructures present during the implantation window, such as pinopodes and nucleolar channels, which may prove useful markers of endometrial receptivity Bentin-Ley et al. Methods that associate morphology and function e.

Unfortunately, immunohistochemistry suffers from the same problems as morphological assessments. In the future, laser capture microdissection may be coupled with gene expression analysis, providing another useful tool that could be used to link endometrial morphology and function Yanaihara et al.

Another key consideration when using endometrial dating is that it disregards the status of the embryo. Ensuring the endometrium is receptive is of little use if a poor-quality embryo is introduced. Therefore, to ensure optimal conditions for implantation, endometrial dating should not be used in isolation, but should be combined with other techniques that provide information about embryo quality.

Progesterone and estrogen are the dominant hormonal modulators of endometrial development. Ovarian estrogen and progesterone condition the uterus for implantation, and knowledge about the precise temporal action of these hormones within the menstrual cycle has allowed the development of hormone-based contraception. Both the epithelial and stromal compartments express progesterone and estrogen receptors, and the response depends on the levels of these receptors as well as on the concentration of the hormones themselves.

The interactions of progesterone and estrogen with estrogen receptors ER during endometrial development are illustrated in Fig. It is apparent that the appropriate cyclical pattern of receptor expression is crucial for achieving endometrial receptivity and successful implantation Lessey, ; Ma et al.

The roles of progesterone and estrogen E 2 ; E 3 , estriol and estrogen receptors ER during endometrial development. Changes in the expression of progesterone receptors PRA, PRB in glandular epithelial cells and stromal cells during the different phases of the menstrual cycle. Adapted with permission from Mote et al. Although progesterone and estrogen are the key modulators of endometrial maturation, their roles in this process are complex and sophisticated Punyadeera et al. Hormonal activity depends on not only the levels of progesterone, estrogen and their receptors, but also on the rates of progesterone and estrogen metabolism e.

The activities of progesterone and estrogen are also influenced by the effects of co-activators and repressors Punyadeera et al.

In addition to progesterone and estrogen, a number of other endocrinological factors are known to mediate endometrial function Kodaman and Taylor, The effects of androgens are often overlooked in the female reproductive cycle. However, androgen receptors are present on stromal and epithelial cells in the endometrium, and both androstenedione and testosterone induce changes in endometrial function that may be important during implantation Kodaman and Taylor, Endometrial factors are critical mediators of all phases of the implantation process Fig.

Once the embryo reaches the uterus, the first cells it encounters are the epithelial cells of the endometrium. These cells secrete a range of factors into the uterine lumen, which may affect embryonic attachment as well as further development of the early placenta and embryo.

Adapted with permission from Dimitriadis et al. In humans, one factor that has attracted particular interest is leukaemia-inhibitory factor LIF , which is an interleukin IL -6 cytokine expressed in endometrial epithelial cells at the appropriate time for which receptors are present on preimplantation embryos.

Studies in mice demonstrate that LIF plays a role in implantation and may also promote embryonic development. Observational studies in humans are suggestive of a possible role for LIF in humans Robb et al. Indeed, infertility in some women has been associated with the dysregulation of LIF, and also of IL, which is produced in the same manner in the endometrial glands during the receptive phase Dimitriadis et al.

With the increasing trend towards single embryo transfer in ART Vilska et al. Preimplantation genetic diagnosis PGD was initially developed as a preconception test for couples carrying genetic disorders who were at risk of having a child affected by the disorder Thornhill et al. Chromosomal analysis of human gametes and embryos has revealed that chromosome aberrations occur at high frequency in the early preimplantation embryo. Another key issue in ART protocols that is still under debate is the timing of embryo transfer.

Whereas in an unselected patient population a clinical benefit of day-5 transfer blastocyst transfer with respect to live-birth rate and multiple-pregnancy rate has not been shown Blake et al. Blastocyst transfer gives the option to select the morphologically best embryo, whereas it has also been indicated that good-quality blastocysts have a decreased incidence of aneuploidy Fig.

Figure reproduced with permission from Staessen et al. Failure of the blastocyst to release from the zona pellucida has been identified as a potential cause of implantation failure in assisted cycles, particularly in older women Seif et al.

A potential solution to this is artificial disruption of the zona pellucida or assisted hatching. A systematic review of studies investigating the effects of this technique on conception found that assisted hatching significantly improved pregnancy rates, but had no effect on live-birth rates or spontaneous abortion rates, and multiple-pregnancy rates were significantly increased Seif et al. Unfortunately, there were insufficient data for this analysis to investigate the impact of assisted hatching on a number of other important outcomes, such as monozygotic twinning, embryo damage, congenital and chromosomal abnormalities and in vitro blastocyst development.

When optimizing ART procedures to mimic nature as closely as possible, it is important to remember that controlled ovarian stimulation itself interrupts natural physiological processes and is likely to alter key parameters such as the rate of embryonic development and the extent and timing of endometrial receptivity. Artificial stimulation affects the levels of progesterone and estrogen, the ratio between these two hormones and endometrial expression of their receptors Beckers et al.

There is evidence that supraphysiological steroid levels impair the luteal phase, and this is true, even when stimulation is started in the late follicular phase Bourgain et al. Therefore, if the luteal phase is not supplemented, premature luteolysis can occur and pregnancy may not be achieved Beckers et al.

Embryo implants endometrium

Embryo implants endometrium

Embryo implants endometrium