Histological study of decidual spiral arteries and the presence of maternal erythrocytes in the intervillous space during the first trimester of normal human pregnancy

Unveiling the human fetal-maternal interface during the first trimester: biophysical knowledge and gaps

The intricate interplay between the developing placenta and fetal-maternal interactions is critical for pregnancy outcomes. Despite advancements, gaps persist in understanding biomechanics, transport processes, and blood circulation parameters, all of which are crucial for safe pregnancies. Moreover, the complexity of fetal-maternal interactions led to conflicting data and methodological variations. This review presents a comprehensive overview of current knowledge on fetal-maternal interface structures, with a particular focus on the first trimester. More in detail, the embryological development, structural characteristics, and physiological functions of placental chorionic plate and villi, fetal membranes and umbilical cord are discussed. Furthermore, a description of the main structures and features of maternal and fetal fluid dynamic exchanges is provided. However, ethical constraints and technological limitations pose still challenges to studying early placental development directly, which calls for sophisticated in vitro, microfluidic organotypic models for advancing our understanding. For this, knowledge about key in vivo parameters are necessary for their design. In this scenario, the integration of data from later gestational stages and mathematical/computational simulations have proven to be useful tools. Notwithstanding, further research into cellular and molecular mechanisms at the fetal-maternal interface is essential for enhancing prenatal care and improving maternal and fetal health outcomes.

Computational modeling of the interactions between the maternal and fetal circulations in human pregnancy

In pregnancy, fetal growth is supported by its placenta. In turn, the placenta is nourished by maternal blood, delivered from the uterus, in which the vasculature is dramatically transformed to deliver this blood an ever increasing volume throughout gestation. A healthy pregnancy is thus dependent on the development of both the placental and maternal circulations, but also the interface where these physically separate circulations come in close proximity to exchange gases and nutrients between mum and baby. As the system continually evolves during pregnancy, our understanding of normal vascular anatomy, and how this impacts placental exchange function is limited. Understanding this is key to improve our ability to understand, predict, and detect pregnancy pathologies, but presents a number of challenges, due to the inaccessibility of the pregnant uterus to invasive measurements, and limitations in the resolution of imaging modalities safe for use in pregnancy. Computational approaches provide an opportunity to gain new insights into normal and abnormal pregnancy, by connecting observed anatomical changes from high-resolution imaging to function, and providing metrics that can be observed by routine clinical ultrasound. Such advanced modeling brings with it challenges to scale detailed anatomical models to reflect organ level function. This suggests pathways for future research to provide models that provide both physiological insights into pregnancy health, but also are simple enough to guide clinical focus. We the review evolution of computational approaches to understanding the physiology and pathophysiology of pregnancy in the uterus, placenta, and beyond focusing on both opportunities and challenges. This article is categorized under: Reproductive System Diseases >Computational Models.

Early first trimester uteroplacental flow and the progressive disintegration of spiral artery plugs: new insights from contrast-enhanced ultrasound and tissue histopathology

STUDY QUESTION

Does the use of a vascular contrast agent facilitate earlier detection of maternal flow to the placental intervillous space (IVS) in the first trimester of pregnancy?

SUMMARY ANSWER

Microvascular filling of the IVS was demonstrated by contrast-enhanced ultrasound from 6 weeks of gestation onwards, earlier than previously believed.

WHAT IS KNOWN ALREADY

During placental establishment and remodeling of maternal spiral arteries, endovascular trophoblast cells invade and accumulate in the lumen of these vessels to form 'trophoblast plugs'. Prior evidence from morphological and Doppler ultrasound studies has been conflicting as to whether the spiral arteries are completely plugged, preventing maternal blood flow to the IVS until late in the first trimester.

STUDY DESIGN, SIZE, DURATION

Uteroplacental flow was examined across the first trimester in human subjects given an intravenous infusion of lipid-shelled octofluoropropane microbubbles with ultrasound measurement of destruction and replenishment kinetics. We also performed a comprehensive histopathological correlation using two separately archived uteroplacental tissue collections to evaluate the degree of spiral artery plugging and evaluate remodeling of the upstream myometrial radial and arcurate arteries.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pregnant women (n = 34) were recruited in the first trimester (range: 6+3 to 13+6 weeks gestation) for contrast-enhanced ultrasound studies with destruction-replenishment analysis of signal intensity for assessment of microvascular flux rate. Histological samples from archived in situ (Boyd Collection, n = 11) and fresh first, second, and third trimester decidual and post-hysterectomy uterine specimens (n = 16) were evaluated by immunohistochemistry (using markers of epithelial, endothelial and T-cells, as well as cell adhesion and proliferation) and ultrastructural analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Contrast agent entry into the IVS was visualized as early as 6+3 weeks of gestation with some variability in microvascular flux rate noted in the 6-7+6 week samples. Spiral artery plug canalization was observed from 7 weeks with progressive disintegration thereafter. Of note, microvascular flux rate did not progressively increase until 13 weeks, which suggests that resistance to maternal flow in the early placenta may be mediated more proximally by myometrial radial arteries that begin remodeling at the end of the first trimester.

LIMITATIONS REASONS FOR CAUTION

Gestational age was determined by crown-rump length measurements obtained by transvaginal ultrasound on the day of contrast-enhanced imaging studies, which may explain the variability in the earliest gestational age samples due to the margin of error in this type of measurement.

WIDER IMPLICATIONS OF THE FINDINGS

Our comprehensive in situ histological analysis, in combination with the use of an in vivo imaging modality that has the sensitivity to permit visualization of microvascular filling, has allowed us to reveal new evidence in support of increasing blood flow to the IVS from 6 weeks of gestation. Histologic review suggested the mechanism may be blood flow through capillary-sized channels that form through the loosely cohesive 'plugs' by 7 weeks gestation. However, spiral artery remodeling on its own did not appear to explain why there is significantly more blood flow at 13 weeks gestation. Histologic studies suggest it may be related to radial artery remodeling, which begins at the end of the first trimester.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by the Oregon Health and Science University Knight Cardiovascular Institute, Center for Developmental Health and the Struble Foundation. There are no competing interests.

Feeding Your Baby In Utero: How the Uteroplacental Circulation Impacts Pregnancy

The utero-placental circulation links the maternal and fetal circulations during pregnancy, ensuring adequate gas and nutrient exchange, and consequently fetal growth. However, our understanding of this circulatory system remains incomplete. Here, we discuss how the utero-placental circulation is established, how it changes dynamically during pregnancy, and how this may impact on pregnancy success, highlighting how we may address knowledge gaps through advances in imaging and computational modeling approaches.

Oxygen tension regulates the miRNA profile and bioactivity of exosomes released from extravillous trophoblast cells - Liquid biopsies for monitoring complications of pregnancy

Our understanding of how cells communicate has undergone a paradigm shift since the recent recognition of the role of exosomes in intercellular signaling. In this study, we investigated whether oxygen tension alters the exosome release and miRNA profile from extravillous trophoblast (EVT) cells, modifying their bioactivity on endothelial cells (EC). Furthermore, we have established the exosomal miRNA profile at early gestation in women who develop pre-eclampsia (PE) and spontaneous preterm birth (SPTB). HTR-8/SVneo cells were used as an EVT model. The effect of oxygen tension (i.e. 8% and 1% oxygen) on exosome release was quantified using nanocrystals (Qdot®) coupled to CD63 by fluorescence NTA. A real-time, live-cell imaging system (Incucyte™) was used to establish the effect of exosomes on EC. Plasma samples were obtained at early gestation (<18 weeks) and classified according to pregnancy outcomes. An Illumina TrueSeq Small RNA kit was used to construct a small RNA library from exosomal RNA obtained from EVT and plasma samples. The number of exosomes was significantly higher in EVT cultured under 1% compared to 8% oxygen. In total, 741 miRNA were identified in exosomes from EVT. Bioinformatic analysis revealed that these miRNA were associated with cell migration and cytokine production. Interestingly, exosomes isolated from EVT cultured at 8% oxygen increased EC migration, whilst exosomes cultured at 1% oxygen decreased EC migration. These changes were inversely proportional to TNF-α released from EC. Finally, we have identified a set of unique miRNAs in exosomes from EVT cultured at 1% oxygen and exosomes isolated from the circulation of mothers at early gestation, who later developed PE and SPTB. We suggest that aberrant exosomal signalling by placental cells is a common aetiological factor in pregnancy complications characterised by incomplete SpA remodeling and is therefore a clinically relevant biomarker of pregnancy complications.

Positive and negative effects of cellular senescence during female reproductive aging and pregnancy

Cellular senescence is a phenomenon occurring when cells are no longer able to divide even after treatment with growth stimuli. Because senescent cells are typically associated with aging and age-related diseases, cellular senescence is hypothesized to contribute to the age-related decline in reproductive function. However, some data suggest that senescent cells may also be important for normal physiological functions during pregnancy. Herein, we review the positive and negative effects of cellular senescence on female reproductive aging and pregnancy. We discuss how senescent cells accelerate female reproductive aging by promoting the decline in the number of ovarian follicles and increasing complications during pregnancy. We also describe how cellular senescence plays an important role in placental and fetal development as a beneficial process, ensuring proper homeostasis during pregnancy.

Physiopathology of human embryonic implantation: clinical incidences

Embryo implantation consists of a series of events promoting the invasion of the endometrium and then the uterine arterial system by the extra-embryonic trophoblast. In order for this semi-heterologous implantation to succeed, the endometrium has to first undergo a number of structural and biochemical changes (decidualization). The decidua's various constituents subsequently play a role in the embryonic implantation. The third step is the transformation of the uterine vascular system and the growth of the placenta, which will provide the foetoplacental unit with nutrients. Several physiopathological aspects will be discussed: 1) the implantation window, regulated by maternal and embryonic hormonal secretions and thus influenced by any defects in the latter: dysharmonic luteal phase, 21-hydroxylase block, abnormal integrin expression, 2) the successive trophoblast invasions of uterine vessels which, when defective, lead to early embryo loss or late-onset vascular pathologies, as preeclampsia, 3) the pregnancy's immunological equilibrium, with a spontaneously tolerated semi-allogeneic implant, 4) the impact of pro-coagulant factors (thrombophilia) on the pregnancy's progression, 5) the environment of the uterus, ranging from hydrosalpinx to uterine contractions. In summary, the least anatomical or physiological perturbation can interfere with human embryonic implantation - a very particular phenomenon and a true biological paradox.

Inflammatory and Epigenetic Pathways for Perinatal Depression

Depression during the perinatal period is common and can have adverse consequences for women and their children. Yet, the biobehavioral mechanisms underlying perinatal depression are not known. Adverse early life experiences increase the risk for adult depression. One potential mechanism by which this increased risk occurs is epigenetic embedding of inflammatory pathways. The purpose of this article is to propose a conceptual model that explicates the linkage between early life adversity and the risk for maternal depression. The model posits that early life adversity embeds a proinflammatory epigenetic signature (altered DNA methylation) that predisposes vulnerable women to depression during pregnancy and the postpartum period. As proposed, women with a history of early life adversity are more likely to exhibit higher levels of proinflammatory cytokines and lower levels of oxytocin in response to the demands of pregnancy and new motherhood, both of which are associated with the risk for perinatal depression. The model is designed to guide investigations into the biobehavioral basis for perinatal depression, with emphasis upon the impact of early life adversity. Testing this model will provide a better understanding of maternal depressive risk and improve identification of vulnerable women who would benefit from targeted interventions that can reduce the impact of perinatal depression on maternal–infant health.

Sera from early-onset, severely preeclamptic women directly modulate HLA-E expression in the EA.hy296 endothelial cell line

The expression of endothelial HLA-E in the context of the systemic inflammatory response observed in preeclampsia has not been established. An experimental study was designed to determine the effect of the sera of pregnant women on the expression of HLA-E in EA.hy296 endothelial cells. First, measurements of protein fractions were performed in sera from early-onset, severely preeclamptic women without HELLP syndrome, in which there was no significant difference in total proteins between the groups, but a reduced level of plasma albumin and an increase in α1-globulin were observed in both groups of pregnant women compared with non-pregnant women. Measurements of colloid osmotic pressure (COP) using a recalculated albumin/globulin ratio formula determined only a significant decrease in COP in all pregnant groups compared with non-pregnant women. The expression of membrane HLA-E was increased in EA.hy296 endothelial cells stimulated with sera of early-onset, severely preeclamptic women, while recombinant interferon-γ (IFN-γ) significantly reduced the expression of membrane HLA-E. Pro-inflammatory cytokines were measured by Luminex in the serum samples, and increased levels of tumor necrosis factor (TNF) and decreased levels of IFN-γ were observed in early-onset, severe preeclampsia compared with normal pregnancy. Moreover, soluble HLA-E was detected in these serum samples by Western blot and ELISA, but no significant difference was found. This raises the possibility that a systemic inflammatory response promotes a compensatory mechanism of COP balance in severe preeclampsia by release of inflammation-induced factors, including endothelial HLA-E. Evidence is now provided regarding HLA-E expression by EA.hy296 cells.

Cross-species withdrawal of MCL1 facilitates postpartum uterine involution in both the mouse and baboon

A successful postpartum involution permits the postnatal uterus to rapidly regain its prepregnancy function and size to ultimately facilitate an ensuing blastocyst implantation. This study investigates the molecular mechanisms that govern the initiation of the involution process by examining the signaling events that occur as the uterus transitions from the pregnant to postnatal state. Using mouse and baboon uteri, we found a remarkable cross-species conservation at the signal transduction level as the pregnant uterus initiates and progresses through the involution process. This study originated with the observation of elevated levels of caspase-3 activation in both the laboring mouse and baboon uterus, which we found to be apoptotic in nature as evidenced by the concurrent appearance of cleaved poly(ADP-ribose) polymerase. We previously defined a nonapoptotic and potential tocolytic role for uterine caspase-3 during pregnancy regulated by increased antiapoptotic signaling mediated by myeloid cell leukemia sequence 1 and X-linked inhibitor of apoptosis. In contrast, this study determined that diminished antiapoptotic signaling in the postpartum uterus allowed for both endometrial apoptotic and myometrial autophagic episodes, which we speculate are responsible for the rapid reduction in size of the postpartum uterus. Using our human telomerase immortalized myometrial cell line and the Simian virus-40 immortalized endometrial cell line (12Z), we demonstrated that the withdrawal of antiapoptotic signaling was also an upstream event for both the autophagic and apoptotic processes in the human uterine myocyte and endometrial epithelial cell.

Manifestations of immune tolerance in the human female reproductive tract

Like other mucosal surfaces (e.g., the gastrointestinal tract, the respiratory tract), the human female reproductive tract acts as an initial barrier to foreign antigens. In this role, the epithelial surface and subepithelial immune cells must balance protection against pathogenic insults against harmful inflammatory reactions and acceptance of particular foreign antigens. Two common examples of these acceptable foreign antigens are the fetal allograft and human semen/sperm. Both are purposely deposited into the female genital tract and appropriate immunologic response to these non-self antigens is essential to the survival of the species. In light of the weight of this task, it is not surprising that multiple, redundant and overlapping mechanisms are involved. For instance, cells at the immunologic interface between self (female reproductive tract epithelium) and non-self (placental trophoblast cells or human sperm) express glycosylation patterns that mimic those on many metastatic cancer cells and successful pathogens. The cytokine/chemokine milieu at this interface is altered through endocrine and immunologic mechanisms to favor tolerance of non-self. The “foreign” cells themselves also play an integral role in their own immunologic acceptance, since sperm and placental trophoblast cells are unusual and unique in their antigen presenting molecule expression patterns. Here, we will discuss these and other mechanisms that allow the human female reproductive tract to perform this delicate and indispensible balancing act.

Placental apoptosis in health and disease

Apoptosis, programmed cell death, is an essential feature of normal placental development but is exaggerated in association with placental disease. Placental development relies upon effective implantation and invasion of the maternal decidua by the placental trophoblast. In normal pregnancy, trophoblast apoptosis increases with placental growth and advancing gestation. However, apoptosis is notably exaggerated in the pregnancy complications, hydatidiform mole, pre-eclampsia, and intrauterine growth restriction (IUGR). Placental apoptosis may be initiated by a variety of stimuli, including hypoxia and oxidative stress. In common with other cell-types, trophoblast apoptosis follows the extrinsic or intrinsic pathways culminating in the activation of caspases. In contrast, the formation of apoptotic bodies is less clearly identified, but postulated by some to involve the clustering of apoptotic nuclei and liberation of this material into the maternal circulation. In addition to promoting a favorable maternal immune response, the release of this placental-derived material is thought to provoke the endothelial dysfunction of pre-eclampsia. Widespread apoptosis of the syncytiotrophoblast may also impair trophoblast function leading to the reduction in nutrient transport seen in IUGR. A clearer understanding of placental apoptosis and its regulation may provide new insights into placental pathologies, potentially suggesting therapeutic targets.

First-trimester 3-dimensional power Doppler of the uteroplacental circulation space: a potential screening method for preeclampsia

OBJECTIVE

The objective of the study was to compare 3-dimensional power Doppler (3DPD) of the uteroplacental circulation space (UPCS) in the first trimester between women who develop preeclampsia (PEC) and those who do not and to assess the 3DPD method as a screening tool for PEC.

STUDY DESIGN

This was a prospective observational study of singleton pregnancies at 10 weeks 4 days to 13 weeks 6 days. The 3DPD indices, vascularization index (VI), flow index (FI), and vascularization flow index (VFI), were determined on a UPSC sphere biopsy with the virtual organ computer-aided analysis (VOCAL) program.

RESULTS

Of 277 women enrolled, 24 developed PEC. The 3DPD indices were lower in women who developed PEC. The area under the receiver-operating characteristics curve for the prediction of PEC was 78.9%, 77.6%, and 79.6% for VI, FI, and VFI, respectively.

CONCLUSION

Patients who develop PEC have lower 3DPD indices of their UPCS during the first trimester. Our findings suggest that this ultrasonographic tool has the potential to predict the development of PEC.

Intervillous and uteroplacental circulation in normal early pregnancy and early pregnancy loss assessed by 3-dimensional power Doppler angiography

OBJECTIVE

To assess intervillous and uteroplacental circulation in early normal pregnancies and miscarriages.

STUDY DESIGN

One hundred normal pregnancies and 46 delayed miscarriages were evaluated by 3-dimensional vaginal ultrasound and power Doppler angiography. Volumes of the early placenta and the subplacental area were obtained between 5 and 12.6 weeks' gestation. The placental volume, vascularization index, flow index, and vascularization flow index was calculated.

RESULTS

Intraclass correlation coefficients ranged from 0.961 for placental volume to 0.885 for intervillous flow index. Intervillous power Doppler signals were not detected before the sixth week. Placental volume (R(2) = 0.68), intervillous vascularization index (R(2) = 0.30), flow index (R(2) = 0.33) and vascularization flow index (R(2) = 0.35), uteroplacental flow index (R(2) = 0.34), and vascularization flow index (R(2) = 0.17) increase significantly (P < .001) throughout the first trimester of normal pregnancies. Uteroplacental vascularization index was not significantly related to gestational age. Intervillous vasculariztion index, flow index, and vascularization flow index were significantly raised in miscarriages, but there were no significant differences for uteroplacental vascularization index, flow index, or vascularization flow index.

CONCLUSION

Intervillous and uteroplacental blood flow increases throughout the first trimester of normal pregnancies. Intervillous circulation is abnormally increased when a miscarriage is diagnosed.

Trophoblast-mediated spiral artery remodelling: a role for apoptosis

In the first 20 weeks of pregnancy a number of important changes take place in the maternal uterine vasculature. Vascular endothelial and smooth muscle cells are lost from the spiral arteries and are replaced by fetal trophoblast cells. The resulting increase in blood flow to the intervillous space ensures that the fetus receives the nutrients and respiratory gases required for growth. Failure of the vessels to remodel sufficiently is a common feature of pregnancy pathologies such as early pregnancy loss, intrauterine growth restriction and pre-eclampsia. Although there is evidence to suggest that some vascular changes occur prior to trophoblast invasion, it is clear that in the absence of trophoblast invasion the remodelling of the spiral arteries is reduced. The cellular and molecular mechanisms by which trophoblasts influence vessel structure have been little studied. Trophoblasts synthesize and release a plethora of cytokines and growth factors including members of the tumour necrosis factor family such as tumour necrosis factor alpha, Fas-ligand and tumour necrosis factor-related apoptosis-inducing ligand. Recent studies suggest that these factors may be important in regulating the remodelling process by inducing both endothelial cell and vascular smooth muscle cell apoptosis.

Increased apoptosis in first trimester extravillous trophoblasts from pregnancies at higher risk of developing preeclampsia

Preeclampsia complicates 5 to 10% of pregnancies and is a leading cause of maternal and fetal mortality and morbidity. Although the cause is unknown, inadequate invasion and remodeling of maternal uterine arteries by extravillous trophoblasts (EVTs) in the first trimester is a common feature. Uterine spiral artery resistance as detected by Doppler ultrasound is commonly used in the second trimester to identify pregnancies destined to develop preeclampsia. Correlation between high uterine resistance and the failure of trophoblast invasion has been reported as early as 12 weeks. However, the reason for this failure has not been established. Understanding the processes involved would significantly improve our diagnostic potential. In this study, we correlated increased first trimester uterine artery resistance with a biological abnormality in trophoblast function. EVTs derived from high-resistance pregnancies were more sensitive to apoptotic stimuli than those from normal-resistance pregnancies. Survival of EVTs from high-resistance pregnancies could be increased by nitric oxide, whereas inhibition of nitric oxide in cells from normal-resistance pregnancies increased apoptotic sensitivity. This predates the onset of symptoms by several weeks and provides evidence for a mechanism responsible for the incomplete uterine vessel remodeling and the differences in artery resistance between preeclamptic and normal pregnancies.

Subinvolution of the placental site as an anatomic cause of postpartum uterine bleeding: a review

CONTEXT

Subinvolution of the placental site is an anatomic cause of delayed postpartum uterine bleeding that may be underrecognized by general surgical pathologists.

OBJECTIVE

To review the physiology of uteroplacental arterial development and normal postpartum involution, and to present the characteristic clinical and histopathologic features of subinvolution.

DATA SOURCES

Literature review (MEDLINE via PubMed and Ovid) regarding the pathology and pathophysiology of placental site subinvolution. Review of the clinical and pathologic characteristics of our own institution's previously diagnosed cases of subinvolution from hysterectomy and endomyometrial curettage specimens.

CONCLUSIONS

Surgical pathologists must be aware of the cardinal histopathologic findings of subinvolution, and this diagnosis must be considered in every postpartum curettage or hysterectomy specimen presented to the surgical pathologist. Subinvolution of the placental site is an important diagnosis, as this process implies an idiopathic cause, rather than an iatrogenic cause, of postpartum uterine bleeding. The etiology of placental site subinvolution remains poorly characterized.

The Uterine Spiral Arteries In Human Pregnancy: Facts and Controversies

Uterine spiral arteries play a vital role in supplying nutrients to the placenta and fetus, and for this purpose they are remodelled into highly dilated vessels by the action of invading trophoblast (physiological change). Knowledge of the mechanisms of these changes is relevant for a better understanding of pre-eclampsia and other pregnancy complications which show incomplete spiral artery remodelling. Controversies still abound concerning different steps in these physiological changes, and several of these disagreements are highlighted in this review, thereby suggesting directions for further research. First, a better definition of the degree of decidua- versus trophoblast-associated remodelling may help to devise a more adequate terminology. Other contestable issues are the vascular plugging and its relation with oxygen, trophoblast invasion from the outside or the inside of the vessels (intravasation versus extravasation), the impact of haemodynamics on endovascular migration, the replacement of arterial components by trophoblast, maternal tissue repair mechanisms and the role of uterine natural killer (NK) cells. Several of these features may be disturbed in complicated pregnancies, including the early decidua-associated vascular remodelling, vascular plugging and haemodynamics. The hyperinflammatory condition of pre-eclampsia may be responsible for vasculopathies such as acute atherosis, although the overall impact of such lesions on placental function is far from clear. Several features of the human placental bed are mirrored by processes in other species with haemochorial placentation, and studying such models may help to illuminate poorly understood aspects of human placentation.

First-trimester trophoblast cell model gene response to hypoxia

OBJECTIVE

Trophoblast invasion, which sets the stage for placentation and pregnancy outcome, likely occurs in a hypoxic environment. We used microarray technology in a trophoblast cell line to identify hypoxia-responsive genes that may impact placentation.

STUDY DESIGN

An immortalized extravillous cytotrophoblast cell line, HTR-8/SVneo, was exposed to normoxia (20% oxygen) or hypoxia (1% oxygen) for 6 hours. Total RNA was harvested and prepared for microarray study. Quantitative reverse transcriptase polymerase chain reaction was performed for array confirmation.

RESULTS

We confirmed the up- and down-regulation of 10 hypoxia-responsive genes using quantitative reverse transcriptase polymerase chain reaction. Ontologic gene categories that were found to be hypoxia-responsive included motility/migration, angiogenesis, and apoptosis.

CONCLUSION

Specific genes that were found to be up-regulated in this first-trimester array (such as plasminogen activator inhibitor-1 and tissue inhibitor of metalloproteinase 3) have been described in preeclampsia. The hypoxia-responsive genes that we identified may be physiologic in early pregnancy. However, up-regulation of these same genes in later pregnancy augurs poorly.

The regulation of trophoblast differentiation by oxygen in the first trimester of pregnancy

In the first trimester of human pregnancy villous cytotrophoblasts are able to differentiate to form either the overlying syncytiotrophoblast layer or, in anchoring villi, extravillous trophoblasts which grow out from the villi and invade into the maternal decidua, acting to both physically attach the placenta to the decidua, and modify the maternal spiral arteries to sustain pregnancy. During the first 10-12 weeks of gestation, extravillous trophoblast plugs block the spiral arteries and prevent maternal blood flow entering the intervillous space, thereby creating an environment of physiological hypoxia in which placental and fetal development occur. As extravillous trophoblasts migrate away from the villus they differentiate from a proliferative to an invasive phenotype. The hypoxic environment of the first trimester is believed to play an important role in the regulation of trophoblast differentiation. However, there is currently a large body of conflicting experimental evidence concerning this topic. This review examines the experimental evidence to date on the role of oxygen in trophoblast differentiation.

A prospective, longitudinal study of the renin–angiotensin system, prostacyclin and thromboxane in the first trimester of normal human pregnancy: association with birthweight

BACKGROUND

Very early human pregnancy is a state of cardiovascular underfilling. The renin-angiotensin system (RAS) is directly concerned with sodium and water homeostasis. Angiotensinogen is known to be the rate-limiting component in the generation of angiotensin I, and hence angiotensin II, in pregnancy. The usual measurement of 'renin activity' does not differentiate between enzyme and substrate. We hypothesized that the RAS is activated from the start of pregnancy; plasma renin concentration (PRC) and angiotensinogen will show differential regulation and might stimulate the rise in prostacyclin.

METHODS

A prospective study of 12 nulliparous normal women. PRC and angiotensinogen and excretion of prostacyclin and thromboxane metabolites were measured pre-pregnancy and four to six times after conception to 13 weeks.

RESULTS

By 6 weeks gestation, mean PRC was markedly raised and remained stable to 13 weeks. The initial angiotensinogen response varied, but rose consistently after 6-8 weeks. Regression analysis showed angiotensinogen in the first trimester to be strongly associated with corrected birthweight centile (P < 0.001). Excretion of eicosanoid metabolites was very variable, but rose significantly from 6 weeks; the ratio between prostacyclin and thromboxane excretion did not alter over this time. There was no correlation between the various hormones measured.

CONCLUSION

Angiotensinogen is known to be rate-limiting in pregnancy. Its association with birthweight may be through effects on early plasma volume expansion and may have implications for intrauterine growth restriction and pre-eclampsia.

Doppler and immunohistochemical evaluation of decidual spiral arteries in early pregnancy

OBJECTIVE

The purpose of this study was to estimate spiral artery subchorionic flow at 8-11 gestational weeks (GW) by Doppler ultrasound and then to analyze these vessels in the decidua basalis using histologic, morphometric and immunohistochemical analyses.

METHODS

Subchorionic spiral arteries were evaluated in 5 women scheduled for aspiration at 8-11 GW. Flow velocity waveforms were sought using color and pulsed Doppler, and the diastolic/systolic (D/S) index was calculated. Transcervical biopsy specimens and aspiration products were thoroughly examined to investigate the structure of the spiral artery at the implantation site using cytotrophoblastic and arterial smooth muscle cell immunohistochemical markers (anti-cytokeratin 7 and anti-actin monoclonal antibodies). Spiral artery cross-sectional inner areas were measured and compared with the D/S index in each case.

RESULTS

Low-impedance pulsatile flow could be detected below the trophoblastic ring in all cases. Complete obstruction of a spiral artery lumen was never observed and cytotrophoblastic cells were incorporated into the vessel wall starting from the perivascular cuff.

CONCLUSION

Both techniques evidenced that decidual spiral arteries in the placental bed are not completely obstructed at 8-11 GW.

Pathophysiology of preeclampsia: links with implantation disorders

The phenomenon of implantation anchors the embryo into the uterine wall and produces a hemochorial placenta that maintains the pregnancy and fetal growth. Implantation and placentation are intimately linked and cannot be dissociated either in time or in space. Preeclampsia is characterized by hypertension and proteinuria. It is secondary to an anomaly of the invasion of the uterine spiral arteries by extra-villous cytotrophoblast cells, associated with local disruptions of vascular tone, of immunological balance and inflammatory status, and sometimes with genetic predispositions. Preeclampsia is a disease of early pregnancy, a form of incomplete spontaneous abortion, but is expressed late in pregnancy. Aspirin may play a favorable role in implantation which is related to the genesis of preeclampsia and some cases of intra-uterine growth restriction. The most important points in obtaining a preventive effect from low-dose aspirin during the pregnancy are early treatment (before 13 weeks of gestation) and the prescription of a sufficient dose (more than 100 mg per day).

Trophoblast invasion of spiral arteries: a novel in vitro model

Extravillous trophoblasts invade the uterine wall (interstitial invasion) and the spiral arteries (endovascular invasion), replacing the cells of the vessel wall and creating a high-flow low-resistance vessel. We have developed a novel model to allow the interactions between the invading trophoblast cells and the cells of the spiral artery to be directly examined. Unmodified (non-placental bed) spiral arteries were obtained from uterine biopsies at caesarean section. Fluorescently labelled trophoblasts were seeded on top of artery segments embedded in fibrin gels (to study interstitial invasion) or perfused into the lumen of arteries mounted on a pressure myograph (to study endovascular invasion). Trophoblasts were incubated with the vessels for 3-5 days prior to cryo-sectioning. Both interstitial and endovascular interactions/invasion could clearly be detected and a comparison of the extravillous trophoblast cell line, SGHPL-4 and primary first trimester cytotrophoblasts showed both to be invasive in this model. This novel method will prove useful in an area where in vitro studies have been hampered by the lack of suitable models directly examining cellular interactions during invasion.

Uteroplacental circulation development: Doppler assessment and clinical importance

In the first weeks of pregnancy, columns of endovascular cytotrophoblastic plugs develop in the lumen of spiral arteries. Morphologic data show that these plugs become loosened as soon as the end of the second month and the intervillous circulation of maternal blood is likely to be established progressively between the 8th and 12th weeks. The disorganization of the musculo-elastic layers of these vessels provokes a dramatic decrease in vascular tone in the uteroplacental circulation. These modifications appear to govern the establishment of a low-pressure blood flow in the placenta, and hence determine the quality of uteroplacental circulation and normal fetal growth. Placental bed biopsies in women with pre-eclampsia and in a proportion of pregnancies with intrauterine growth retardation have shown that these physiologic changes were absent in the myometrial segments of spiral arteries. Recently, colour Doppler was used to assess intervillous and spiral artery flow in early pregnancy, confirming in vivo free intervillous flow at 12 weeks and a progressive significant decrease in spiral artery resistance with advancing gestation during the first trimester. However, certain data at an earlier gestational age are still contradictory. Particularly, the exact nature of the contents of the intervillous space before 8 weeks, and whether or not this fluid can be considered maternal blood, remains controversial.

[Detection of fetal cells in maternal blood: myth or reality?]

Fetal cells exist in maternal blood and can be utilized for prenatal diagnosis. These cells are present from the sixth week of gestation, with frequency increasing as gestation advances, to many years after the birth. Enrichment of trophoblast cells, erythroblasts and lymphocytes was performed with various density gradient techniques and either magnetic activated or fluorescent activated sorting techniques. The abnormalities were detected by fluorescent in-situ hybridation (FISH) with chromosome-specific DNA probes for the detection of trisomy 21, trisomy 18, Klinefelter syndrome 47 XXY, or by polymerase chain reaction (PCR) for the detection of fetal sex, certain Mendelian disorders (as beta-globin mutations), HLA polymorphisms and fetal Rhesus D blood type. However others studies were necessary to determine the sensitivity and specificity of this technique as a noninvasive alternative to conventional methods of prenatal cytogenetic diagnosis.

Uterine haemodynamics as a possible driving force for endovascular trophoblast migration in the placental bed

Uteroplacental vascular adaptation during pregnancy depends on retrograde endovascular migration of trophoblast in the uterine spiral arteries and their subsequent incorporation into the vessel wall. In the human, this migration process occurs in a step-wise fashion, starting with plugging of the distal ends of the arteries, followed by migration into the decidual and, after several weeks' delay, into the myometrial segments. The hypothesis is put forward that haemodynamical forces play an important regulatory role in this process. A mechanical signal transduction system should then be present within the trophoblastic cells to trigger their rheotactic behaviour. Since the condition of preeclampsia is characterized by restricted colonization of spiral arteries by trophoblast, the implications of this proposed regulatory system on the pathogenesis of the disease are considered.

Localization and significance of urokinase plasminogen activator and its receptor in placental tissue from intrauterine, ectopic and molar pregnancies

Urokinase plasminogen activator receptor (uPAR) is a membrane-anchored protein with urokinase plasminogen activator (uPA) as the ligand. This complex induces proteolysis and remodelling of maternal decidua during placental implantation. The presence of uPAR on trophoblasts is supposed to promote adhesion, migration and invasion. In cancer tissue, high levels of uPAR are correlated with a poor prognosis. This immunohistochemical study shows the localization of uPA and uPAR in a prospective design with stereological sampling of fetal and maternal tissue from normal, ectopic and hydatidiform molar (HM) pregnancies. Cytokeratin and Ki67 were used as markers for trophoblasts and proliferating cells. Membrane-bound uPAR was observed on villous non-proliferating intermediate trophoblasts (IT) within cell columns in intrauterine and ectopic pregnancies. The corresponding proliferating IT with cytological atypia sprouting from the chorionic villi in HM was uPAR-negative. uPA but not uPAR was observed in anchoring distal IT at the attachment-point to the basal plate. In the placental bed, extravillous interstitial trophoblasts were uPA-positive but uPAR-negative. The trophoblast giant cells were both uPA- and uPAR-negative. In relation to the maternal vessels, a focal distribution for uPA and uPAR was present in the endovascular and perivascular trophoblasts. The intraluminal trophoblasts overlying endothelial cells were uPAR-positive only. In maternal tissue from intrauterine and molar pregnancies, uPAR was seen in the decidual cells in a zone facing the anchoring villi and the fibrinoid lesions with embedded trophoblasts. In contrast, the stromal cells of the fallopian tube without a decidual reaction facing the implanted gestation were uPAR-negative. Non-invaded decidual, myometrial and muscular tissue of the pregnant uterus and fallopian tube was extensively positive for uPA whereas 'pseudodecidual' cells from the intrauterine evacuate in patients with an ectopic pregnancy only showed a focal and scanty reaction for uPA. When trophoblast invasion of the decidua was present, the decidual cells were uPA-negative. A semi-quantitative assessment of the receptor was estimated in villous IT within cell columns in normal and molar pregnancies but, in conclusion, quantitative evaluation of uPAR cannot be used to predict development of post-molar persistent trophoblastic disease (PTD).

Maternal arterial connections to the placental intervillous space during the first trimester of human pregnancy: the Boyd collection revisited

OBJECTIVE

We sought to determine morphologically when the maternal uterine circulation to the human placenta is established.

STUDY DESIGN

We performed a histologic review of 12 early-pregnancy hysterectomy specimens contained within the Boyd Collection, ranging from 43 to 130 days' gestation.

RESULTS

Before the eighth week of pregnancy, maternal arterial connections with the intervillous space are restricted to tortuous networks of intercellular spaces. Only after this period can direct channels be observed. Initially, these are of small caliber, but they become sizable and clearly delineated after 11 to 12 weeks.

CONCLUSION

The maternal circulation to the placenta must be extremely sluggish before the eighth week of pregnancy but will be gradually established over the next few weeks. It is unlikely to be substantial until at least 12 weeks. The implication is that development of the human fetoplacental unit during most of the first trimester takes place in a low-oxygen environment.

Susceptibility of human placental syncytiotrophoblastic mitochondria to oxygen-mediated damage in relation to gestational age

When maintaining first trimester placental villi in organ culture under conventional normoxic conditions, we have observed widespread degeneration of the syncytiotrophoblast within 24 h despite excellent viability for the cytotrophoblastic and stromal cell types. Here we identify loss of mitochondrial activity as an early event in this process. In the light of proposals that the early part of gestation occurs in a low oxygen environment and also reported associations between mitochondrial disruption and oxidative stress, we cultured first trimester villi under low oxygen conditions (2.5%). Mitochondrial superoxide dismutase (MnSOD) localization and activity at different gestational ages were also determined. It was found that syncytiotrophoblastic and mitochondrial morphology improved, and mitochondrial activity was retained for 6 h and more if 8- to 10-week-old tissue was placed into a low oxygen environment immediately after removal from the uterus. The effect of oxygen concentration was less marked when using tissue of 14 weeks or more gestational age, which showed good survival and retention of mitochondrial activity under both low and ambient oxygen conditions. This correlated with our finding that placental MnSOD activity increased significantly between 8 and 14 weeks of gestation. Immunohistochemistry demonstrated that at 11 weeks; MnSOD was localized predominantly within the cytotrophoblast cells, whereas by 16 weeks it was found in the syncytiotrophoblast also. These results indicate an acute sensitivity of first trimester placenta syncytiotrophoblast to oxygen-mediated damage.