Thirteen placentas were studied from 5 normal pregnancies and 8 from pregnancies complicated by fetal growth restriction (4 with present, 3 with absent, and 1 with reversed end-diastolic velocities at Doppler interrogation of the umbilical arteries). On immunohistochemically stained slides, the diameter (d) and the wall thickness (t) of the arterial vasculature of the stem villi were measured for a total of approximately 10,000 vessels. A multivariate ‘mixed effect model’ statistical analysis was performed using d and t as dependent variables and gestational age, delivery mode, fetal and placental weight, the degree of vascular collapse and Doppler blood flow patterns as independent variables. Gestational age, Doppler pattern and the degree of vascular collapse significantly affected both d and t, the mode of delivery influenced d while fetal and placental weights scarcely affected the dependent variables. The above parameters should therefore be taken into account when investigating placental stem vessel morphometry.

Human embryogenesis takes place in a hypoxic environment because the trophoblast shell excludes entry of maternal blood. The first fetal-placental villi develop as trophoblast sprouts. These are invaded by allantoic mesoderm to form secondary villi and are transformed, by vasculogenesis, into tertiary villi. The placental barrier to maternal blood is gradually breached between 8-12 weeks of gestation, due to invasion of placental-bed uteroplacental spiral arteries by the extravillous trophoblast (EVT). Placental oxygen tension thus rises and a phase of branching angiogenesis continues until 24 weeks. Thereafter a gradual shift takes place favoring non-branching angiogenesis. Gas-exchanging terminal villi thus form which are essential for rapid fetal growth and development of a high-flow, low-resistance fetal-placental circulation. Inadequate invasion of the uteroplacental spiral arteries by EVT results in placental ischemia and the development of obstetrical complications--preeclampsia and/or intrauterine growth restriction (IUGR). Placental villi often show evidence of continued branching angiogenesis, as is the case with anemic pregnancy, and pregnancy at high altitude. These structural alterations may reflect continued hypoxia-driven activity of vascular endothelial growth factor (VEGF). By contrast, a minority of severe early-onset IUGR pregnancies exhibit reduced fetal-placental blood flow with elongated maldeveloped villous capillaries. Placenta-like growth factor (PIGF) expression is increased while trophoblast proliferation is reduced, suggesting "hyperoxia" in the placental villous tree. IUGR may thus have two phenotypes--a more common hypoxic and a rarer hyperoxic type. While this concept is gaining acceptance, we have no insight as to the initiating mechanism(s).

Objective: To test the hypothesis that the characteristics of umbilical artery Doppler flow velocity waveforms in growth-restricted fetuses indicate angiogenesis within placental stem and gas-exchanging villi.Methods: We examined 18 placentas from singleton fetuses that were normal structurally and chromosomally but were growth-restricted, preterm, and complicated by preeclampsia. Ten cases with positive end-diastolic flow and eight with absent or reverse end-diastolic flow were compared with six gestational age-matched controls. Sections of villous placenta were examined to determine structural composition (percentage of fibrinoid, intervillous space, and villous tissue), relative proportion of villous types (stem, immature intermediate, and gas-exchanging villi), and the frequency distribution of stem arterial vessel calibers and their branching pattern.Results: Placentas with positive end-diastolic flow had a significantly (P <.05) higher percentage of gas-exchanging villi (median 69.6%, range 62.5-80.8%) than those with absent or reverse end-diastolic now (58.3%, 29.9-71.9%) or controls (60.8%, 43.1-65.6%). The gas-exchanging villi from placentas with absent or reverse end-diastolic now were slender, elongated, poorly branched, and poorly capillarized. There was a progressive trend toward reduced branching of the stem arteries from the controls (median 22%, range 2-38%), through the positive end-diastolic group (17%, 11-20%), to the absent or reverse end-diastolic group (13%, 4-23%).Conclusion: Compared with absent or reverse end-diastolic flow the placentas from growth-restricted fetuses with positive end-diastolic flow showed a normal pattern of stem artery development, accompanied by increased capillary angiogenesis and terminal villous development. These features suggest an adaptive pathway for the placenta in the face of uteroplacental ischemia. (Obstet Gynecol 1999;93: 499-503. (C) 1999 by The American College of Obstetricians and Gynecologists.).

OBJECTIVE: In contrast to tubal abortions, viable ectopic pregnancies in color Doppler ultrasonography exhibit a signal-intensive ring around the gestational sac. We investigated the underlying differences in implantation and placentation.STUDY DESIGN: Histologic sections of fallopian tubes carrying viable tubal pregnancies (13 patients) and tubal pregnancies that aborted (8 patients) were immunostained for cytokeratin, MIB-1, CD-34, and CD-68. The data were studied by computer-aided image analysis followed by statistical evaluation (Student t test, P <.05).RESULTS: In contrast to tubal abortions, viable tubal pregnancies are characterized by implantation at the mesosalpingial rather than at the antimesosalpingial side of the organ. They exhibit deeper trophoblast invasion into the thickened tubal wall, more intense trophoblast proliferation (P <.001), and increased villous vascularization(P<.001).CONCLUSION: The morphologic findings correlate with preoperative Doppler ultrasonography. They suggest that trophoblast invasion, placental growth, and the fate of tubal pregnancies depend on the implantation site. They encourage a conservative management of anti-mesosalpingially implanted, nonviable ectopic pregnancies in clinically stable patients.

Background Epidemiological studies describe an association between relative size of the placenta at delivery and cardiovascular morbidity and mortality during adult life. Some determinants of placental size, such as maternal anaemia, have been acknowledged, but no plausible mechanism has been advanced to explain the initiation of postnatal disease. Methods Placental villous vascularisation in anaemic women (Hb < 90 g/L) was assessed in the first and third trimesters of pregnancy by immunohistochemical identification of villous capillaries and compared with that of gestational age-matched groups of women with normal (Hb>110 g/L; control group) concentrations of haemoglobin, and an intermediate group (Hb 90-110 g/L). Findings Anaemia, especially in the first trimester, was associated with increased numbers of capillaries per villous cross section (mean 11·70 [SE 0·35] vs 4·14 [0·27]) located mainly in the outer third of the stroma beneath the trophoblast (94% [1·15] vs 67% [1·82]) and with increased numbers of villous macrophages and of proliferating MIB-1-positive cells compared with the control group. Interpretation Maternal anaemia in early pregnancy seems to influence the pattern of placental vascularisation. Such changes might alter placental vascular impedance during early fetal life, thereby exerting important effects on cardiovascular development.

Pre-eclampsia remains a leading cause of maternal and infant morbidity and mortality. Insufficient invasion of trophoblast cells into the myometrial portions of the spiral arteries is thought to play a crucial role in the development of pre-eclampsia. As a consequence, uteroplacental vessels fail to undergo adaptive changes which are imperative to provide a sufficient blood supply to the placenta. Consecutive placental hypoxia is supposed to cause secretion/shedding of still unidentified placental metabolites resulting in different forms of pregnancy-induced hypertension. This review presents published data concerning the causes of insufficient trophoblast invasion in preeclampsia. Expression of HLA-G by extravillous trophoblast cells seems to be altered, resulting in activation of the maternal immune system. The pattern of integrin expression as well as the secretion of proteases is reported to be disturbed, which could lead to a reduced invasive potential of the trophoblast cells. Recent data indicate a pathophysiological role of NK-cells and macrophages in the altered trophoblast invasion. In summary, preeclampsia seems to be induced by a multifactorial disturbance of trophoblast invasiveness which is characterised by reduced invasiveness of the trophoblast cells themselves and by an activated maternal immune response blocking the invasion by the semiallogenic trophoblast.

Hypertensive Schwangerschaftserkrankungen gehören auch heute noch zu den häufigsten Ursachen der mütterlichen und kindlichen Morbidität und Mortalität. Weitgehend anerkannt ist eine im Zentrum der Pathogenese stehende mangelhafte Invasion von extravillösen Trophoblastzellen in die myometranen Segmente der Spiralarterien. Die damit verbundene inadäquate Adaptation dieser Gefäße an den drastisch erhöhten Durchblutungsbedarf des Uterus in der Schwangerschaft hat eine plazentare Hypoxie zur Folge, die über eine Freisetzung bisher unbekannter Mediatoren letztlich zu dem heterogenen Bild hypertensiver Schwangerschaftskomplikationen führen soll. Die Ursachen dieser insuffizienten Trophoplastinvasion sind bisher nicht hinreichend geklärt. In der Literatur finden sich Hinweise für eine verminderte HLA-G Expression der Trophoplastzellen bei Präeklampsie. In der Folge könnte es zu einer verschlechterten Maskierung dieser Zellen gegenüber dem maternalen Immunsystem und damit zur Induktion einer maternalen Immunantwort kommen. Daneben wurde über ein verändertes Integrinexpressionsmuster auf der Trophoblastoberfläche berichtet. Als Folge wird eine Nichtausprägung des erforderlichen endothelartigen Phänotyps bei endovaskulären Trophoblastzellen diskutiert, außerdem eine beeinträchtigte Invasionsfähigkeit des Trophoblasten. Die gleiche Folge hat möglicherweise eine veränderte Sekretion von matrixauflösenden Proteasen durch invadierende Trophoblastzellen bei Präeklampsie. Hier sind die Ergebnisse allerdings noch widersprüchlich. Aktuelle Untersuchungen lassen vermuten, daß auch immunkompetente Zellen (NK-Zellen. Makrophagen) bei der gestörten Trophoblastinvasion eine pathophysiologische Bedeutung aufweisen. So haben zahlreiche von ihnen sezernierte Zytokine einen modulierenden Einfluß auf Trophoblastwachstum und -motilität. Darüber hinaus könnten immunkompetente Zellen auch eine Beeinträchtigung des Prostaglandinstoffwechsels, der bei Präeklampsie verändert ist, verursachen. Es ist denkbar, daß eine Veränderung im Gleichgewicht dieser vasoaktiven Substanzen im Plazentabett die Dilatation der uteroplazentaren Arterien behindert. Dies kann auch durch genetisch determinierte Varianten des Angiotensinogens verursacht werden. Darüber hinaus werden diese pathologischen Angiotensinogen-Varianten mit möglichen atherotischen Veränderungen der Spiralarterien in Verbindung gebracht. Obwohl ein schlüssiges Gesamtkonzept für die gestörte Trophoblastinvasion bei Präeklampsie derzeit noch nicht erstellt werden kann, muß man von einem Zusammenwirken multipler Faktoren ausgehen.

During the first trimester of pregnancy, the human placenta is an actively dividing and highly invasive tumour-like tissue, while near term, it represents a fully developed, non-invasive unit. In order to understand the molecular basis of this marked difference in the placental phenotypes, an approach based on a differential display–reverse transcription–polymerase chain reaction (DD–RT–PCR) was adopted to analyse changes in gene expression, using total RNA isolated from first-trimester and term placental villi. Using this approach, T-plastin was initially identified as being differentially expressed in the human first-trimester placenta. T-plastin is an actin-bundling protein and is known to be highly expressed in actively dividing cells and up-regulated in several carcinomas. Using a homogenous population of cytotrophoblasts and syncytiotrophoblasts isolated from human placentae, the present authors demonstrate the differential expression of T-plastin in cytotrophoblasts compared with the terminally differentiated syncytiotrophoblasts. The down-regulation of T-plastin expression is further demonstrated in human trophoblastic BeWo cells induced to differentiate using transforming growth factor (TGF)β1, a growth factor known for its anti-proliferative and anti-invasive response in placental cells. These studies suggest that expression of T-plastin in the placental context may indeed be associated with the enhanced replicative potential of placental trophoblasts.

In human pregnancy, trophoblasts are the only cells of fetal origin in direct contact with the maternal immune system: syncytiotrophoblasts are in contact with maternal blood, whereas extravillous trophoblasts are in contact with numerous maternal uterine natural killer (NK) cells. Therefore, trophoblasts are thought to play a key role in maternal tolerance to the semiallogeneic fetus, in part through cytokine production and NK cell interaction. Epstein-Barr virus-induced gene 3 (EBI3) encodes a soluble hematopoietin receptor related to the p40 subunit of interleukin-12. Previous studies indicated that EBI3 is expressed in the spleen and tonsils, and at high levels in full-term placenta. To investigate further EBI3 expression throughout human pregnancy, we generated monoclonal antibodies specific for EBI3 and developed an EBI3 enzyme-linked immunosorbent assay. Immunohistochemical experiments with EBI3 monoclonal antibody on first-, second-, and third-trimester placental tissues demonstrated that EBI3 was expressed throughout pregnancy by syncytiotrophoblasts and extravillous trophoblasts (cytotrophoblast cell columns, interstitial trophoblasts, multinucleated giant cells, and trophoblasts of the chorion laeve). EBI3 expression was also induced during in vitro differentiation of trophoblast cell lines. In addition, large amounts of secreted EBI3 were detected in explant cultures from first-trimester and term placentae. Consistent with these data, EBI3 levels were strongly up-regulated in sera from pregnant women and gradually increased with gestational age. These data, together with the finding that EBI3 peptide is presented by HLA-G, suggest that EBI3 is an important immunomodulator in the fetal-maternal relationship, possibly involved in NK cell regulation.

ABSTRACT Objective To assess the elaboration of placental stem villous vessels from pregnancies complicated by intrauterine growth restriction (IUGR) with absent end–diastolic flow velocity detected prior to delivery in the umbilical artery. Design Comparison between IUGR and control groups of the distribution, in 15 pm increments of 600 randomly chosen stem vessel profiles (post‐fixation diameter 10‐160 pm) identified by immunohistochemical localisation of a‐smooth muscle actin in the vessel media. Setting Clinical teaching hospital and university anatomy department. Subjects Paraffin‐fixed blocks obtained from placentas of eight pregnancies complicated by IUGR and eight gestational age‐matched controls. Results The distribution of the stem villous vessels in the IUGR placentas, as assessed by the mean vessel diameter in each case, did not differ from the controls (mean vessel diameter 31.8 μm [SD 2.41 vs 29.6 pm [2.3]; P = 0.13 ). In five IUGR cases a‐smooth muscle actin positive cells (myofibroblasts) were identified within the stroma of nonmuscularised peripheral (mature intermediate and terminal) villi, but in none of the controls. Conclusions Our data do not support the theory that IUGR with absent end‐diastolic flow velocity in the umbilical artery is due to a selective loss of small stem villous vessels. The increased impedance in this condition may be conferred more distally within the nonmuscularised capillaries of the peripheral villi.

Topological analysis was applied to investigate the branching pattern of three specimens obtained from early human placenta (6, 9, and 16 weeks p.m.) reconstructed on the basis of semi-thin sections. Centripetal Horton-Strahler and centrifugal branching order nomenclature was used for topological description of the analysed tree-like structures. Bifurcation ratio and vertex ratio were determined for all three cases and were found to be relatively constant. It was shown that branching pattern is closely related to the model of random segment branching that implicates a high level of asymmetry and a small level of space limitation for branching. The significance of this approach for the analysis of development of the villous tree, for the analysis of mesenchymal villous heterogeneity, and for the estimation of physiological parameters for fetoplacental exchange is discussed. We suggest that topological analysis can lead to a new quantitative classification of branching patterns of the human placental villous trees in normal and pathologic pregnancies.

Objective: To test the hypothesis that the characteristics of umbilical artery Doppler flow velocity waveforms in growth-restricted fetuses indicate angiogenesis within placental stem and gas-exchanging villi.Methods: We examined 18 placentas from singleton fetuses that were normal structurally and chromosomally but were growth-restricted, preterm, and complicated by preeclampsia. Ten cases with positive end-diastolic flow and eight with absent or reverse end-diastolic flow were compared with six gestational age-matched controls. Sections of villous placenta were examined to determine structural composition (percentage of fibrinoid, intervillous space, and villous tissue), relative proportion of villous types (stem, immature intermediate, and gas-exchanging villi), and the frequency distribution of stem arterial vessel calibers and their branching pattern.Results: Placentas with positive end-diastolic flow had a significantly (P < .05) higher percentage of gas-exchanging villi (median 69.6%, range 62.5–80.8%) than those with absent or reverse end-diastolic flow (58.3%, 29.9–71.9%) or controls (60.8%, 43.1–65.6%). The gas-exchanging villi from placentas with absent or reverse end-diastolic flow were slender, elongated, poorly branched, and poorly capillarized. There was a progressive trend toward reduced branching of the stem arteries from the controls (median 22%, range 2–38%), through the positive end-diastolic group (17%, 11–20%), to the absent or reverse end-diastolic group (13%, 4–23%).Conclusion: Compared with absent or reverse end-diastolic flow, the placentas from growth-restricted fetuses with positive end-diastolic flow showed a normal pattern of stem artery development, accompanied by increased capillary angiogenesis and terminal villous development. These features suggest an adaptive pathway for the placenta in the face of uteroplacental ischemia.

Nach der lichtmikroskopischen und der dreidimensionalen Struktur der mesenchymalen Zotte soll mit den hier vorgestellten Befunden die beschriebene strukturelle Dreiteilung in Zottenbasis, Mittelteil und Spitzenregion auf ultrastrukturellem Niveau weiter untersucht werden. Um die Schlußfolgerungen zur funktionellen Bedeutung der Dreiteilung zu überprüfen, wurde darüber hinaus autoradiographisch die Zellteilungsrate bestimmt.