Placenta - Maternal Decidua

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Anchoring Villi and Maternal Decidua

This page gives an overview of aspects of maternal component of placental development, formed initially by the decidualization of the endometrium.

In week 2, the trophoblast shell cells proliferate and form a syncitiotrophoblast and cytotrophoblast layer around the conceptus. Syncitiotrophoblast cells migrate into the uterine wall, forming maternal blood-filled spaces (lacunae).

Decidualization is the process of converting endometrial stromal cells into decidual cells and requires at least 8–10 days of hormone stimulation. A similar "decidual" cellular change, but less significant, also occurs in the uterine lining after ovulation during the secretory phase of the non-pregnant uterus.

  • initiated during the mid-secretory phase of the menstrual cycle
  • in response to elevated progesterone levels
  • acts mainly through progesterone receptor (PR) PR-A (other isoform is PR-B)

Placentation begins once the conceptus begins to implant in the uterine wall and the placenta will have both a fetal and a maternal component.

During pregnancy, both the maternal blood volume increases by about 50% and the uterine blood flow increases 10 to 12 fold. Flow increase is due to the trophoblast cell invasion of the spiral arteries opening them into blood-filled spaces of the placenta.

For the non-pregnant uterus background see Menstrual Cycle and Uterus Development.

Placenta Links: placenta | Lecture - Placenta | Lecture Movie | Practical - Placenta | implantation | placental villi | trophoblast | maternal decidua | uterus | endocrine placenta | placental cord | placental membranes | placenta abnormalities | ectopic pregnancy | Stage 13 | Stage 22 | placenta histology | placenta vascular | blood vessel | cord stem cells | 2013 Meeting Presentation | Placenta Terms | Category:Placenta
Historic Embryology - Placenta 
1883 Embryonic Membranes | 1907 Development Atlas | 1909 | 1910 Textbook | 1917 Textbook | 1921 Textbook | 1921 Foetal Membranes |1921 human | 1921 Pig implantation | 1922 Single placental artery | 1923 Placenta Review | 1939 umbilical cord | 1943 human and monkey | 1944 chorionic villus and decidua parietalis | 1946 placenta ageing | 1960 first trimester placenta | 1960 monkey | 1972 Placental circulation | Historic Disclaimer

Some Recent Findings

  • Review - Regulation of Placental Extravillous Trophoblasts by the Maternal Uterine Environment[1] "During placentation invasive extravillous trophoblasts (EVTs) migrate into the maternal uterus and modify its vessels. In particular, remodeling of the spiral arteries by EVTs is critical for adapting blood flow and nutrient transport to the developing fetus. Failures in this process have been noticed in different pregnancy complications such as preeclampsia, intrauterine growth restriction, stillbirth, or recurrent abortion. Upon invasion into the decidua, the endometrium of pregnancy, EVTs encounter different maternal cell types such as decidual macrophages, uterine NK (uNK) cells and stromal cells expressing a plethora of growth factors and cytokines. Here, we will summarize development of the EVT lineage, a process occurring independently of the uterine environment, and formation of its different subtypes. Further, we will discuss interactions of EVTs with arteries, veins and lymphatics and illustrate how the decidua and its different immune cells regulate EVT differentiation, invasion and survival. The present literature suggests that the decidual environment and its soluble factors critically modulate EVT function and reproductive success."
  • Three macrophage subsets are identified in the uterus during early human pregnancy[2] "Macrophages are crucial for a successful pregnancy, and malfunctions of decidual macrophages correlate with adverse pregnancy outcomes, such as spontaneous abortion and preeclampsia. Previously, decidual macrophages were often thought to be a single population. In the present study, we identified three decidual macrophage subsets, CCR2-CD11cLO (CD11clow, ~80%), CCR2-CD11cHI (CD11chigh, ~5%), and CCR2+CD11cHI (CD11chigh, 10-15%), during the first trimester of human pregnancy by flow cytometry analysis. CCR2-CD11cLO macrophages are widely distributed in the decidua, while CCR2-CD11cHI and CCR2+CD11cHI macrophages are primarily detected close to extravillous trophoblast cells according to immunofluorescence staining."
  • IFPA meeting 2016 workshop report III: Decidua-trophoblast interactions; trophoblast implantation and invasion; immunology at the maternal-fetal interface; placental inflammation[3] "Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At IFPA meeting 2016 there were twelve themed workshops, four of which are summarized in this report. These workshops related to various aspects of placental biology but collectively covered areas of decidual-trophoblast interaction, regulation of trophoblast invasion, immune cells at the maternal-fetal interface, and placental inflammation."
  • Systematic Analysis of the Molecular Mechanism Underlying Decidualization Using a Text Mining Approach[4] "Decidualization is a crucial process for successful embryo implantation and pregnancy in humans. Defects in decidualization during early pregnancy are associated with several pregnancy complications, such as pre-eclampsia, intrauterine growth restriction and recurrent pregnancy loss. However, the mechanism underlying decidualization remains poorly understood. In the present study, we performed a systematic analysis of decidualization-related genes using text mining. We identified 286 genes for humans and 287 genes for mice respectively, with an overlap of 111 genes shared by both species. Through enrichment test, we demonstrated that although divergence was observed, the majority of enriched gene ontology terms and pathways were shared by both species, suggesting that functional categories were more conserved than individual genes. We further constructed a decidualization-related protein-protein interaction network consisted of 344 nodes connected via 1,541 edges."
More recent papers  
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Search term: Maternal Decidua | Decidua Basalis

Older papers  
These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.

See also the Discussion Page for other references listed by year and References on this current page.

  • Leukocyte driven-decidual angiogenesis in early pregnancy[5] "Successful pregnancy and long-term, post-natal maternal and offspring cardiac, vascular and metabolic health require key maternal cardiovascular adaptations over gestation. Within the pregnant decidualizing uterus, coordinated vascular, immunological and stromal cell changes occur. ...One of the earliest uterine responses to pregnancy in species with hemochorial placentation is stromal cell decidualization, which creates unique niches for angiogenesis and leukocyte recruitment. In early decidua basalis, the aspect of the implantation site that will cradle the developing placenta and provide the major blood vessels to support mature placental functions, leukocytes are greatly enriched and display specialized properties. UNK cells, the most abundant leukocyte subset in early decidua basalis, have angiogenic abilities and are essential for normal early decidual angiogenesis."
  • Disordered IL-33/ST2 activation in decidualizing stromal cells prolongs uterine receptivity in women with recurrent pregnancy loss[6] "Decidualization renders the endometrium transiently receptive to an implanting blastocyst although the underlying mechanisms remain incompletely understood. Here we show that human endometrial stromal cells (HESCs) rapidly release IL-33, a key regulator of innate immune responses, upon decidualization. In parallel, differentiating HESCs upregulate the IL-33 transmembrane receptor ST2L and other pro-inflammatory mediators before mounting a profound anti-inflammatory response that includes downregulation of ST2L and increased expression of the soluble decoy receptor sST2. We demonstrate that HESCs secrete factors permissive of embryo implantation in mice only during the pro-inflammatory phase of the decidual process. IL-33 knockdown in undifferentiated HESCs was sufficient to abrogate this pro-inflammatory decidual response. Further, sequential activation of the IL-33/ST2L/sST2 axis was disordered in decidualizing HESCs from women with recurrent pregnancy loss. Signals from these cultures prolonged the implantation window but also caused subsequent pregnancy failure in mice. Thus, Il-33/ST2 activation in HESCS drives an autoinflammatory response that controls the temporal expression of receptivity genes. Failure to constrain this response predisposes to miscarriage by allowing out-of-phase implantation in an unsupportive uterine environment."

Maternal Decidua

Placenta and Decidua[7]

The maternal uterine endometrium stromal cells (fibroblast-like) are transformed by steroid hormones (progesterone) and embryonic signals into the decidua.

The entire maternal decidua is divided into three regions: decidua basalis, decidua capsularis and decidua parietals (decidua vera).

These 3 regions are named by their positional relationship to the conceptus.

Human placenta SERPINE2 expression 02.jpg

Immunostained placenta and decidua.[7]

SERPINE2 was extensively detected in decidual cells (dc), cytotrophoblasts, extravillous trophoblasts at the junction zone of the cell column (cc) and anchoring villi (av), and the endothelia of the spiral artery (sa); and weak staining was found in fibrinoids (f) and the villous mesenchyme.

Maternal Immune

How does the implanting conceptus avoid immune rejection by the maternal immune system? There are a number of maternal and embryonic mechanisms that are thought to act to prevent immune rejection of the implanting conceptus, though the complete mechanism(s) are unknown. This is particularly relevant to Assisted Reproductive Technology involving donor eggs.

Below are some examples of research on this topic.

Decidual Immune Cells

Specialised immune cells.
Decidual Macrophages (Mϕ) Decidual T cells Uterine Natural Killer cells
  • Macrophages represent about 20% of all leukocytes.
  • regulatory role at the fetal-maternal interface.
  • M2 macrophage phenotype involved in tissue remodeling and inhibit inflammation
  • maintenance of tolerance to the non-self semi-allogeneic fetus
  • activated by fetal HLA-C (expressed on extravillous trophoblast cells)
  • specific immune tolerance to fetal alloantigens
  • Killer Inhibitory Receptor (KIR) activation by fetal HLA-C (expressed on extravillous trophoblast cells)

Uterine Natural Killer Cells

See also article on peripheral NK cells. Tim-3 signaling in peripheral NK cells promotes maternal-fetal immune tolerance and alleviates pregnancy loss

Decidual Mast Cells

Immune system mast cells generally occur in two subtypes: (positive, +; negative, -) tryptase+/chymase- and tryptase+/chymase+.

In teh maternal placenta tryptase positive(+) mast cells are present.[8]

  • FcεRIα+Kit+tryptase+chymase+ phenotype.
  • release histamine following FcεRI aggregation.

A recent study of non-pregnant uterus identified the presence of a third mast cell subtype (tryptase-/chymase+). [9]

Chemokine Gene Silencing

Remove the attraction of maternal immune cells.

A mouse study[10] has shown that the normal immune response to inflammation, accumulation of effector T cells in response to chemokine secretion does not occur during implantation. This is prevented locally by epigenetic silencing of chemokine expression in the decidual stromal cells.

Corticotropin-Releasing Hormone

Kill the maternal immune cells.

Both maternal and implanting conceptus release CRH at the embryo implantation site. This hormone then binds to receptors on the surface of trophoblast (extravillous trophoblast) cells leading to expression of a protein (Fas ligand, FasL) that activates the extrinsic cell death pathway on any local maternal immune cells ( T and B lymphocytes, natural killer cells, monocytes and macrophages).[11] (Note - This cannot be the only mechanism, as mice with dysfunctional FasL proteins are still fertile).

Decidualization Factors

There are a number of known molecular signals involved in the conversion of uterine stromal cells into decimal cells.

Preimplantation Factor

  • Preimplantation factor (PIF) secreted only by viable embryos.
  • a 15 amino acid peptide MVRIKPGSANKPSDD
  • regulates immunity, promoting embryo-decidual adhesion, and regulating adaptive apoptotic processes.[12]

Activin A

Member of the a transforming growth factor beta (TGFbeta) superfamily, contributes to human endometrial stromal cells (HESC) decidualization and has been localized to decidual cells in the human endometrium. (possibly also BMP2 and TGFbeta1)[13]

Prokineticin 1

Prokineticin 1 (PROK1) signalling via prokineticin receptor 1 (PROKR1) regulates Dickkopf 1 (DKK1) expression, a negative regulator of canonical Wnt signaling.[14]

Macrophage Inhibitory Cytokine

Macrophage inhibitory cytokine (MIC-1) or Growth/Differentiation Factor 15 (GDF15) or Bone Morphogenetic Protein, Placenta (PLAB)

Inhibits trophoblast invasion by blocking activation of MMP-2 and -9, as well as stimulating apoptosis.



  1. Pollheimer J, Vondra S, Baltayeva J, Beristain AG & Knöfler M. (2018). Regulation of Placental Extravillous Trophoblasts by the Maternal Uterine Environment. Front Immunol , 9, 2597. PMID: 30483261 DOI.
  2. Jiang X, Du MR, Li M & Wang H. (2018). Three macrophage subsets are identified in the uterus during early human pregnancy. Cell. Mol. Immunol. , 15, 1027-1037. PMID: 29618777 DOI.
  3. Aplin JD, Beristain A, DaSilva-Arnold S, Dunk C, Duzyj C, Golos TG, Kemmerling U, Knöfler M, Mitchell MD, Olson DM, Petroff M, Pollheimer J, Reyes L, Schedin P, Soares MJ, Stencel-Baerenwald J, Thornburg KL & Lash GE. (2017). IFPA meeting 2016 workshop report III: Decidua-trophoblast interactions; trophoblast implantation and invasion; immunology at the maternal-fetal interface; placental inflammation. Placenta , 60 Suppl 1, S15-S19. PMID: 28456431 DOI.
  4. Liu JL & Wang TS. (2015). Systematic Analysis of the Molecular Mechanism Underlying Decidualization Using a Text Mining Approach. PLoS ONE , 10, e0134585. PMID: 26222155 DOI.
  5. Lima PD, Zhang J, Dunk C, Lye SJ & Croy BA. (2014). Leukocyte driven-decidual angiogenesis in early pregnancy. Cell. Mol. Immunol. , 11, 522-37. PMID: 25066422 DOI.
  6. Salker MS, Nautiyal J, Steel JH, Webster Z, Sućurović S, Nicou M, Singh Y, Lucas ES, Murakami K, Chan YW, James S, Abdallah Y, Christian M, Croy BA, Mulac-Jericevic B, Quenby S & Brosens JJ. (2012). Disordered IL-33/ST2 activation in decidualizing stromal cells prolongs uterine receptivity in women with recurrent pregnancy loss. PLoS ONE , 7, e52252. PMID: 23300625 DOI.
  7. 7.0 7.1 Chern SR, Li SH, Chiu CL, Chang HH, Chen CP & Tsuen Chen EI. (2011). Spatiotemporal expression of SERPINE2 in the human placenta and its role in extravillous trophoblast migration and invasion. Reprod. Biol. Endocrinol. , 9, 106. PMID: 21806836 DOI.
  8. Matsuno T, Toyoshima S, Sakamoto-Sasaki T, Kashiwakura JI, Matsuda A, Watanabe Y, Azuma H, Kawana K, Yamamoto T & Okayama Y. (2018). Characterization of human decidual mast cells and establishment of a culture system. Allergol Int , , . PMID: 29784282 DOI.
  9. De Leo B, Esnal-Zufiaurre A, Collins F, Critchley HOD & Saunders PTK. (2017). Immunoprofiling of human uterine mast cells identifies three phenotypes and expression of ERβ and glucocorticoid receptor. F1000Res , 6, 667. PMID: 28620462 DOI.
  10. Nancy P, Tagliani E, Tay CS, Asp P, Levy DE & Erlebacher A. (2012). Chemokine gene silencing in decidual stromal cells limits T cell access to the maternal-fetal interface. Science , 336, 1317-21. PMID: 22679098 DOI.
  11. Makrigiannakis A, Zoumakis E, Kalantaridou S, Coutifaris C, Margioris AN, Coukos G, Rice KC, Gravanis A & Chrousos GP. (2001). Corticotropin-releasing hormone promotes blastocyst implantation and early maternal tolerance. Nat. Immunol. , 2, 1018-24. PMID: 11590404 DOI.
  12. Paidas MJ, Krikun G, Huang SJ, Jones R, Romano M, Annunziato J & Barnea ER. (2010). A genomic and proteomic investigation of the impact of preimplantation factor on human decidual cells. Am. J. Obstet. Gynecol. , 202, 459.e1-8. PMID: 20452489 DOI.
  13. Stoikos CJ, Harrison CA, Salamonsen LA & Dimitriadis E. (2008). A distinct cohort of the TGFbeta superfamily members expressed in human endometrium regulate decidualization. Hum. Reprod. , 23, 1447-56. PMID: 18434375 DOI.
  14. <pubmed>21546446</pubmed>




Plaisier M. (2011). Decidualisation and angiogenesis. Best Pract Res Clin Obstet Gynaecol , 25, 259-71. PMID: 21144801 DOI.

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Search Pubmed: Maternal Decidua | Decidualization


Placenta Terms (expand to view) 
  • after-birth - term used to describe the delivery of placenta and placental membranes following birth of the child.
  • allantois - An extraembryonic membrane, endoderm in origin extension from the early hindgut, then cloaca into the connecting stalk of placental animals, connected to the superior end of developing bladder. In reptiles and birds, acts as a reservoir for wastes and mediates gas exchange. In mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface.
  • amniocentesis - Clinical term for a prenatal diagnostic test where an ultrasound guided needle is used to extract a sample of the amniotic fluid. Amniocentesis
  • anastomosis - Term used to describe the connection between two tubes. Applied to describe the connection between peripheral blood vessels without an intervening capillary bed.
  • anchoring villi - (stem villi) describes the placental villi (embryonic) that attach to the decidua (maternal) tissue. The tip of the villi consists of a column of trophoblast cells attached to an epithelial plaque.
  • angioblasts form clusters or blood islands on surface of yolk sac.
  • angiogenesis - Term describing the development of new vessels from already existing vessels, this process is secondary to vasculogenesis which is the initial formation of first blood vessels by differentiation of pluripotent mesenchymal cells (extraembryonic mesoderm).
  • capsularis - portion of maternal decidua that covers the conceptus facing towards the uterine cavity.
  • cerebroplacental ratio - (CPR) a doppler ultrasound measurement calculated as the simple ratio between the middle cerebral artery pulsatility index (MCA‐PI) and the umbilical artery pulsatility index (UA‐PI). Fetuses with an abnormal ratio are thought to be a predictor of adverse pregnancy outcome.
  • chorioamnionitis - (CA) An intraamniotic puerperal infection described as having 3 forms: histologic, clinical (clinical chorioamnionitis, IAI), and subclinical. Intraamniotic infection is a common (2-4%) event in labor and the systemic inflammatory response can also lead to preterm birth and neonatal complications.
  • chorion - The extraembryonic membrane generated from trophoblast and extraembryonic mesoderm that forms placenta. chorion and amnion are made by the somatopleure. The chorion becomes incorporated into placental development. The avian and reptilian chorion lies beside the egg shell and allows gas exchange.
  • chorionic cavity - The fluid-filled extraembryonic coelom (cavity) formed initially from trophoblast and extraembryonic mesoderm that forms placenta. chorion and amnion are made by the somatopleure. The chorion becomes incorporated into placental development. The avian and reptilian chorion lies beside the egg shell and allows gas exchange. In humans, this cavity is lost during week 8 when the amniotic cavity expands and fuses with the chorion.
  • chorion frondosum - (frondosum = leafy) The chorion found on conceptus oriented towards maternal blood supply where the majority of villi form and proliferate, will contribute the fetal component of the future placenta.
  • chorion laeve - (laeve = smooth) The smooth chorion found on conceptus away from maternal blood supply (towards uterine epithelium and cavity) with very few villi present.
  • chorionic somatomammotropin - (CSH, human lactogen) A hormone synthesized within the placenta by syncytiotrophoblast cells. This protein hormone (190 amino acid) has a structure is similar to pituitary growth hormone.
  • chorionic villus sampling - (CVS) The taking a biopsy of the placenta, usually at the end of the second month of pregnancy, to test the fetus for genetic abnormalities.
  • coelocentesis - A sampling of extracoelomic fluid usually for an early prenatal diagnostic technique.
  • connecting stalk - the original extra-embryonic mesoderm structure attaching the embryonic disc to the chorion. The placental blood vessels form within this structure.
  • cord blood - (human umbilical cord blood, HUCB) A term used to describe blood collected from the placenta usually after birth. Has been identified as a source of stem cells with potential therapeutic uses and is stored in Cord Blood Banks throughout the world.
  • cord knotting Term describing umbilical or placental cord knotting. This occurs in about 1% prevents the passage of placental blood, pseudoknots also occur usually with no effect.
  • cord presentation - A term used to describe at birth the presence of the umbilical cord between the fetal presenting part and the cervix, with or without membrane rupture.
  • cord prolapse - A term used to describe at birth the descent of the umbilical cord through the cervix alongside (occult) or past (overt) the presenting part in the presence of ruptured membranes (incidence of 0.1% to 0.6%).
  • cotyledon - (Greek, kotyle = a deep cup) In the embryos of seed plants, the "seed leaves," in which nutrients are stored for use after germination. In placental animals, the term is also to describe the leaf-like structure of the placenta surface.
  • cytotrophoblast - The "cellular" trophoblast layer surrounding (forming a "shell") the early implanting conceptus. Beginning at uterine adplantation, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, the syncytiotrophoblast. The cytotrophoblast layer contributes to formation of the placental villi, the functional component of the fetal placenta.
  • decidua basalis - The term given to the uterine endometrium at the site of implantation where signaling transforms the uterine stromal cells (fibroblast-like) into decidual cells. This forms the maternal component of the placenta, the decidualization process gradually spreads through the remainder of the uterus, forming the decidua parietalis.
  • decidua basalis reaction - Term describing the maternal endometrial changes that occur initially at the site of, and following, blastocyst implantation. Seen as a deposition of glycogen, fibrin and proliferation of blood vessels. See also decidualization.
  • decidua capsularis - The term given to the uterine endometrium which has been converted to decidua surrounding the conceptus on the smooth chorion side.
  • decidua parietalis - The term given to the remainder of the uterine endometrium, away from the site of implantation, that gradually becomes comverted to decidua.
  • decidual cell - The uterine stromal cells (fibroblast-like) that differentiate in response to both steroid hormones (progesterone) and embryonic signals. These cells then alter uterine environment to support further embryonic development as well as producing cytokines related to prolactin (PRL) and have an innate immune function.
  • decidual reaction - maternal endometrial reaction invoked in order to block the rapid extension of the implanting syncytium.
  • decidualization - (decidualisation, decidual reaction) The process by which uterine stromal cells differentiate in response to both steroid hormones and embryonic signals into large epitheliod decidual cells. This process is essential for the progress of implantation and establishing fetal-maternal communication.
  • DHEA - (dehydroepiandrosterone, androstenolone) precursor of sex steroid hormones and is converted to testosterone and estradiol. Postnatally, an abundant circulating steroid produced in the adrenal gland. The fetal adrenal cortex produces dehydroepiandrosterone sulfate (DHEA-S) used by the placenta to produce estrogens. DHEA, androstenedione, and testosterone can be metabolized to epiandrosterone, and etiocholanolone. PMID 15635500
  • fetal drug addiction - occurs when drugs used maternally cross the placental barrier and can establish neural/physiological addiction in the unborn fetus. drugs
  • fetal erythroblastosis - (Haemolytic Disease of the Newborn) A clinical term describing an immune response between fetal and maternal blood groups; from fetus Rh+ / maternal Rh-. The leakage of blood from fetus, particularly at birth, causes maternal anti-Rh antibodies, which is then dangerous for a 2nd or future pregnancies.
  • fetal intra-abdominal umbilical vein varix - (FIUV, umbilical vein varix) focal dilatation of the umbilical venous diameter at the level of cord insertion, the dilatation diameter increases linearly with gestational age. Represent about 4% of umbilical cord abnormalities

with an incidence of about 2.8 per 1,000 pregnancies, there is also a rarer form of extra-abdominal varices.PMID 24883288

  • fibrinoid layer - (Nitabuch's layer) A layer formed at maternal/fetal interface during placentation and is thought to act to prevent excessively deep conceptus implantation. Fibrin-type fibrinoid (maternal blood-clot product) and matrix-type fibrinoid (secreted by invasive extravillous trophoblast cells).
  • floating chorionic villi - Term used to describe the placental microanatomy structure of chorionic villi that are not attached to the maternal decidua and float in the maternal blood-filled space (lacunae). Structurally the same as anchoring chorionic villi conceptus side that are attached to the maternal decidua.These villi go through the same stages of development: primary villi - secondary villi - tertiary villi
  • hemotrophic nutrition - Term used to describe in late placenta development the transfer of blood-borne nutrition from maternal to embryo/fetuscompared to early histiotrophic nutrition.
  • heterotopic pregnancy - (Greek, heteros = other) Clinical term for a very rare pregnancy of two or more embryos, consisting of both a uterine cavity embryo implantation and an ectopic implantation.
  • histiotrophic nutrition - Term used to describe in early placenta development the intital transfer of nutrition from maternal to embryo (histiotrophic nutrition) compared to later blood-borne nutrition (hemotrophic nutrition). Histotroph is the nutritional material accumulated in spaces between the maternal and fetal tissues, derived from the maternal endometrium and the uterine glands. This nutritional material is absorbed by phagocytosis initially by blastocyst trophectoderm and then by trophoblast of the placenta. in later placental development nutrition is by the exchange of blood-borne materials between the maternal and fetal circulations, hemotrophic nutrition.
  • Hofbauer cells - Cells found within placental villi connective tissue. Have a role as macrophages of mesenchymal origin with potentially additional functions (remodeling, vasculogenesis, regulation of stromal water content).
  • Human chorionic corticotropin - (hCACTH) placental derived hormone equivilant to corticotropin (ACTH) from the pituitary.
  • Human chorionic gonadotrophin - (hCG) like leutenizing hormone, supports corpus luteum, originally secreted by trophoblast cells.
  • Human chorionic somatommotropin - (hCS, placental lactogen) hormone level increases in maternal blood through pregnancy, decreases maternal insulin sensitivity (raising maternal blood glucose levels and decreasing maternal glucose utilization) aiding fetal nutrition.
  • Template:Hydatiform mole - A uterine tumour with "grape-like" placenta appearance without enclosed embryo formation, arises mainly from a haploid sperm fertilizing an egg without a female pronucleus. It is one form of gestational trophoblastic disease(GTD), a number of abnormalities including hydatiform mole, invasive mole, choriocarcinoma and placental site trophoblastic tumor (PSTT).
  • hysterectomy – clinical term for the surgical removal of the uterus.
  • Langhans layer - cytotrophoblast cell layer.
  • maternal antibodies - antibodies from the mother's immune system that are capable of crossing placental barrier. They can provide immune protection to the embryo, but may also participate in immune disease (fetal erythroblastosis).
  • maternal sinusoids - placental spaces around chorionic villi that are filled with maternal blood. This is the closest maternal/fetal exchange site.
  • Nitabuch's layer - (fibrinoid layer) The layer formed at maternal/fetal interface during placentation and is thought to act to prevent excessively deep conceptus implantation. Fibrin-type fibrinoid (maternal blood-clot product) and matrix-type fibrinoid (secreted by invasive extravillous trophoblast cells).
  • Morbidly adherent placenta (MAP) A general clinical term used to describe the different forms of abnormal placental implantation (Accreta, Increta and Percreta).
  • oligohydramnios - Clinical term for the accumulation a deficiency of amniotic fluid during pregnancy. See also polyhydramnios, an excess of amniotic fluid.
  • persistent right umbilical vein - (PRUV) A placental cord abnormality associated with fetal abnormalities and poor neonatal prognosis. The estimated incidence of persistent right umbilical vein in a low-risk population is 1 : 526. PMID 12047534
  • polyhydramnios - Clinical term for the accumulation of excess amniotic fluid during pregnancy. See also oligohydramnios, a deficiency of amniotic fluid.
  • placenta - (Greek, plakuos = flat cake) The developmental organ formed from maternal and fetal contributions in animals with placental development. In human, the placenta at term is a discoid shape "flat cake" shape; 20 cm diameter, 3 cm thick and weighs 500-600 gm. Placenta are classified by the number of layers between maternal and fetal blood (Haemochorial, Endotheliochorial and Epitheliochorial) and shape (Discoid, Zonary, Cotyledenary and Diffuse). The placenta has many different functions including metabolism, transport and endocrine.
  • placenta accreta - The abnormal placental adherence, either in whole or in part of the placenta with absence of decidua basalis, leading to retention as an after-birth to the underlying uterine wall. The incidence of placenta accreta also significantly increases in women with previous cesarean section compared to those without a prior surgical delivery.
  • placental arteries - (umbilical arteries) In placental animals, the blood vessels which develop within the placental cord carrying relatively deoxygenated blood from the embryo/fetus to the placenta. In humans, there are two placental arteries continuous with the paired internal iliac arteries (hypogastric arteries) arising off the dorsal aortas. At birth this vessel regresses and form the remnant medial umbilical ligament.
  • placental cord - (umbilical cord) The placental cord is the structure connecting the embryo/fetus to the placenta. It is initially extra-embryonic mesoderm forming the connecting stalk within which the placental blood vessels (arteries and veins) form. In human placental cords the placental blood vessels are initially paired, later in development only a single placental vein remains with a pair of placental arteries. This structure also contains the allantois, an extension from the hindgut cloaca then urogenital sinus. Blood collected from the placental cord following delivery is a source of cord blood stem cells.)
  • placental diameter - is measured in the transverse section by calculating the maximum dimensions of the chorionic surface.
  • placental growth factor - (PlGF) A growth factor of the vascular endothelial growth factor (VEGF) family, released from the placental trophoblast cells and other sources that stimulates blood vessel growth.
  • placental malaria - The malarial infection of the placenta by sequestration of the infected red blood cells. This condition can be common in regions where malaria is endemic with women carrying their first pregnancy (primigravida).
  • placenta membranacea - rare placental abnormality characterized by the presence of chorionic villi directly attached to and covering the fetal membranes. Placenta Membranacea
  • placenta previa - placenta overlies internal os of uterus, abnormal bleeding, may require cesarian delivery.
  • placental thickness - is measured at its mid-portion from the chorionic plate to the basilar plate, on a longitudinal plane (less than 4 cm at term). Excludes any abnormalities (fibroids, myometrial contractions, or venous lakes). The placental thickness approximates in millimeters to the weeks of gestation.
  • placental vein - (umbilical vein) In placental animals, the blood vessels which develop within the placental cord carrying relatively oxygenated blood from the placenta to the embryo/fetus. In humans, there are initially two placental veins which fuse to form a single vein. The resence of paired veins in the placental cord can be indicative of developmental abnormalities.
  • placentophagia - Term used to descrbe the maternal ingestion of afterbirth materials (placental membranes and amniotic fluid) that can occur following mammalian parturition (birth).
  • primary villi - (primary chorionic villi) Term describing the earliest stage of embryonic placenta development. In humans, the conceptus during week 2 this first stage of chorionic villi development consists of only the trophoblastic shell cells (syncitiotrophoblasts and cytotrophoblasts) forming finger-like extensions into maternal decidua. Initially these finger-like projections cover the entire surface of chorionic sac and later become restricted to the placental surface. The villi stages are ongoing as the placenta continues to grow through both the embryonic and fetal development.
  • pre-eclampsia - During pregnancy a combination of high blood pressure, protein in urine and fluid retention resulting in maternal sudden excessive swelling of the face, hands and feet. Eclampsia is the subsequent development of convulsions, kidney failure, liver failure, clotting problems or mortality.
  • Rh alloimmunization - feto-maternal haemorrhage generally in late pregnancy results in an Rh-negative woman becoming sensitised to Rh-positive fetal cells that enter her circulation. Clinically treated with anti-D immune globulin prophylaxis, alloimmunization occurs in 9–10% of at-risk pregnancies. immune
  • secondary villi - (secondary chorionic villi) Term describing the second stage of embryonic placenta development. In humans, the conceptus during week 3 onward this stage of chorionic villi development consists of the trophoblastic shell cells (syncytiotrophoblast and cytotrophoblasts) filled with extraembryonic mesoderm forming finger-like extensions into maternal decidua. Initially these finger-like projections cover the entire surface of chorionic sac and later become restricted to the placental surface. The villi stages are ongoing as the placenta continues to grow through both the embryonic and fetal development. Placental villi stages: primary villi - secondary villi - tertiary villi
  • syncytiotrophoblast - A multinucleated cell currently thought to form by the fusion of another trophoblast cell the cytotrophoblasts, within the trophoblast layer (shell) of the implanting conceptus. In early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (Template:Human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy.
  • trophoblast - (trophectoderm, Greek, trophe = "nutrition" and blast = a primordial cell) cells that firstly support adplantation, implantation and endocrine support of pregnancy. Contribute to the extraembryonic tissues, fetal placenta and membranes. Initially form 2 populations individual cytotrophoblast cells and their fused multinucleate syncytiotrophoblast cells.
  • Twin-twin transfusion syndrome - (TTTS) in monozygotic twins with monochorionic and diamniotic placenta, with intrauterine blood transfusion from one twin (donor) to another twin (recipient) where there is an imbalance of blood flow from the donor twin to the recipient twin. Clinically diagnosed by the alternate presence of polyhydramnios in one fetus and oligohydramnios in the co-twin, occurs in about 10% of monochorionic twins.
  • umbilical cord (placental cord) fetal attachment cord 1-2 cm diameter, 30-90cm long, covered with amniotic attached to chorionic plate, umbilical vessels (artery, vein) branch into chorionic vessels. Vessels anastomose within the placenta.
  • umbilical vein varix - (fetal intra-abdominal umbilical vein varix, FIUV) focal dilatation of the umbilical venous diameter at the level of cord insertion, the dilatation diameter increases linearly with gestational age. Represent about 4% of umbilical cord abnormalities

with an incidence of about 2.8 per 1,000 pregnancies, there is also a rarer form of extra-abdominal varices. PMID 24883288

  • vasculogenesis - formation of first blood vessels by differentiation of pluripotent mesenchymal cells (extraembryonic mesoderm) followed by angiogenesis which is the development of new vessels from already existing vessels.
  • vasculosyncytial membranes - localised areas of the placental villous membrane where the barrier thickness separating maternal and fetal circulations is reduced to as little as 1-2 microns. PMID 1287078
  • villi - Plural of villus, which is a thin projection from a surface. The term in development is used to describe the individual functional units together of the fetal placenta.
  • virus - small infectious agents that may cross the placental barrier. Can infect embryo and/or placenta and cause developmental abnormalities. (e.g. cytomegalovirus, rubella, measles).
  • Wharton's jelly - placental cord (umbilical cord) gelatinous connective tissue composed of myofibroblast-like stromal cells, collagen fibers, and proteoglycans. Increases in volume (myxomatous, connective tissue embedded in mucus) at parturition (birth) to assist closure of placental blood vessels. Matrix cells from Wharton's jelly have recently been identified as a potential source of mesenchymal stem cells (MSC), also called mesenchymal stromal cell. This placental cord substance is named after Thomas Wharton (1614-1673) an English physician and anatomist who first described this placental tissue.
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Cite this page: Hill, M.A. (2024, June 22) Embryology Placenta - Maternal Decidua. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G