Current topic: in vivo investigation of the placental circulations by Doppler echography

Spiral, uterine artery doppler and placental ultrasound in relation to preeclampsia

Preeclampsia (PE) is a multiorgan disorder that complicates around 2-8% of pregnancies and is a major cause of perinatal and maternal morbidity and mortality. PE is a clinical syndrome characterized by hypertension secondary to systemic inflammation, endothelial dysfunction, and syncytiotrophoblast stress leading to hypertension and multiorgan dysfunction. The uterine arteries are the main blood vessels that supply blood to the uterus. They give off branches and plays an important role in maintaining blood supply during pregnancy. The arcuate artery originates from the uterine artery and runs medially through the myometrium. The arcuate arteries divide almost directly into anterior and posterior branches, from which the radial artery leads directly to the uterine cavity during their course. Near the endometrium-myometrium junction, the radial artery generates spiral arteries within the basal layer and functional endometrium. The walls of radial and spiral arteries are rich in smooth muscle, which is lost when trophoblast cells invade and become large-caliber vessels. This physiological transformation of uteroplacental spiral arteries is critical for successful placental implantation and normal placental function. In normal pregnancy, the luminal diameter of the spiral arteries is greatly increased, and the vascular smooth muscle is replaced by trophoblast cells. This process and changes in the spiral arteries are called spiral artery remodeling. In PE, this genetically and immunologically governed process is deficient and therefore there is decreased vascular capacitance and increased resistance in the uteroplacental circulation. Furthermore, this defect in uteroplacental spiral artery remodeling is not only associated with early onset PE, but also with fetal growth restriction, placental abruption, and spontaneous premature rupture of membranes. Doppler ultrasound allows non-invasive assessment of placentation, while the flow impedance decreases as the pregnancy progresses in normal pregnancies, in those destined to develop preeclampsia the impedance is increased.

Placenta-Derived Extracellular Vesicles in Pregnancy Complications and Prospects on a Liquid Biopsy for Hemoglobin Bart's Disease

Extracellular vesicles (EVs) are nano-scaled vesicles released from all cell types into extracellular fluids and specifically contain signature molecules of the original cells and tissues, including the placenta. Placenta-derived EVs can be detected in maternal circulation at as early as six weeks of gestation, and their release can be triggered by the oxygen level and glucose concentration. Placental-associated complications such as preeclampsia, fetal growth restriction, and gestational diabetes have alterations in placenta-derived EVs in maternal plasma, and this can be used as a liquid biopsy for the diagnosis, prediction, and monitoring of such pregnancy complications. Alpha-thalassemia major ("homozygous alpha-thalassemia-1") or hemoglobin Bart's disease is the most severe form of thalassemia disease, and this condition is lethal for the fetus. Women with Bart's hydrops fetalis demonstrate signs of placental hypoxia and placentomegaly, thereby placenta-derived EVs provide an opportunity for a non-invasive liquid biopsy of this lethal condition. In this article, we introduced clinical features and current diagnostic markers of Bart's hydrops fetalis, extensively summarize the characteristics and biology of placenta-derived EVs, and discuss the challenges and opportunities of placenta-derived EVs as part of diagnostic tests for placental complications focusing on Bart's hydrop fetalis.

Uterine Radial Artery Resistance Index Predicts Reproductive Outcome in Women with Recurrent Pregnancy Losses and Thrombophilia

Uterine radial artery resistance index (URa-RI) by Doppler ultrasound may reflect the changes in the uteroplacental circulation and be associated with adverse events in early pregnancy. Recurrent pregnancy losses (RPL) are associated with thrombophilia, and anticoagulation treatment with low molecular weight heparin improves pregnancy outcome in women with RPL and thrombophilia. A retrospective cohort study was conducted in 139 pregnant women with 3 or more RPL and thrombophilia. The relationship between pregnancy outcome and dynamic changes of URa-RI was analyzed in 116 women who delivered a liveborn infant and 23 who miscarried the index pregnancy. Patients were on preconception low molecular weight heparin, low-dose aspirin (81mg per day), and prednisone treatment. URa-RI was measured during periovulation time, at the time of positive pregnancy test, and then repeated every two weeks until 32-week gestation or the time of miscarriage. The URa-RI at 8-week gestation was significantly higher in women who miscarried the index pregnancy than those who delivered alive born infant (0.51±0.08 vs. 0.42±0.03, P<0.001). Receiver operating characteristic curve analysis demonstrated that URa-RI of 8 wk gestation effectively distinguished women who miscarried from those who had a live birth with an area under the curve of 82.6% (95% CI 69.01-97.17). After adjusting for covariates including age, BMI, and number of miscarriages, multiple logistic regression models showed that each 0.1 unit increase of URa-RI of 8 wk gestation was associated with 18.70-point increase in the risk of miscarriage (OR19.70, 95%CI 4.26-91.1, P<0.001), and women with an URa-RI≥0.45 had an OR of 49.48 (95% CI 8.01-307.95; P<0.001) for miscarriage compared to those who had URa-RI<0.45. In women with RPL and inherited thrombophilia, increased URa-RI at 8-week gestation was associated with spontaneous abortion independent of other risk factors while they were on anticoagulation treatment.

Visualization of Small-Diameter Vessels by Reduction of Incoherent Reverberation With Coherent Flow Power Doppler

Power Doppler (PD) imaging is a widely used technique for flow detection. Despite the wide use of Doppler ultrasound, limitations exist in the ability of Doppler ultrasound to assess slow flow in the small-diameter vasculature, such as the maternal spiral arteries and fetal villous arteries of the placenta and focal liver lesions. The sensitivity of PD in small vessel detection is limited by the low signal produced by slow flow and the noise associated with small vessels. The noise sources include electronic noise, stationary or slowly moving tissue clutter, reverberation clutter, and off-axis scattering from tissue, among others. In order to provide more sensitive detection of slow flow in small diameter vessels, a coherent flow imaging technique, termed coherent flow PD (CFPD), is characterized and evaluated with simulation, flow phantom experiment studies, and an in vivo animal small vessel detection study. CFPD imaging was introduced as a technique to detect slow blood flow. It has been demonstrated to detect slow flow below the detection threshold of conventional PD imaging using identical pulse sequences and filter parameters. In this paper, we compare CFPD with PD in the detection of blood flow in small-diameter vessels. The results from the study suggest that CFPD is able to provide a 7.5-12.5-dB increase in the signal-to-noise ratio (SNR) over PD images for the same physiological conditions and is less susceptible to reverberation clutter and thermal noise. Due to the increase in SNR, CFPD is able to detect small vessels in high channel noise cases, for which PD was unable to generate enough contrast to observe the vessel.

The role of morphology in mathematical models of placental gas exchange

The performance of the placenta as a gas exchanger has a direct impact on the future health of the newborn. To provide accurate estimates of respiratory gas exchange rates, placenta models need to account for both the physiology of exchange and the organ morphology. While the former has been extensively studied, accounting for the latter is still a challenge. The geometrical complexity of placental structure requires use of carefully crafted approximations. We present here the state of the art of respiratory gas exchange placenta modeling and demonstrate the influence of the morphology description on model predictions. Advantages and shortcomings of various classes of models are discussed, and experimental techniques that may be used for model validation are summarized. Several directions for future development are suggested.

Absence of developmental toxicity in a canine model after infusion of a hemoglobin-based oxygen carrier: Implications for risk assessment

Bovine-derived hemoglobin-based oxygen carriers (HBOCs) have been investigated for use in humans (HBOC-201) and approved for veterinary medicine (HBOC-301). We infused pregnant beagles with HBOC-201 to test whether HBOC-induced developmental toxicity previously observed in rats would occur in a species devoid of an inverted visceral yolk sac (invVYS). Phase 1 assessed developmental toxicity of 6g/kg HBOC-201 on gestational day (GD) 21. Phase 2 investigated single infusions of 6g/kg HBOC-201 on one of GDs 21, 25, 29 or 33. Phase 3 studied multiple sequential infusions on GDs 21, 23,25,27,29, 31, and 33 at 0.52g/kg/day (3.6g/kg total dose). Mild to moderate maternal toxicity occurred in all phases. There was an unequivocal absence of developmental toxicity in all phases. Overall, our hypothesis that HBOC, which interferes with the function of the invVYS, would not affect the offspring in dogs was supported. The implications relative to human risk are discussed.

Placenta-derived exosomes continuously increase in maternal circulation over the first trimester of pregnancy

Background

Human placenta releases specific nanovesicles (i.e. exosomes) into the maternal circulation during pregnancy, however, the presence of placenta-derived exosomes in maternal blood during early pregnancy remains to be established. The aim of this study was to characterise gestational age related changes in the concentration of placenta-derived exosomes during the first trimester of pregnancy (i.e. from 6 to 12 weeks) in plasma from women with normal pregnancies.

Methods

A time-series experimental design was used to establish pregnancy-associated changes in maternal plasma exosome concentrations during the first trimester. A series of plasma were collected from normal healthy women (10 patients) at 6, 7, 8, 9, 10, 11 and 12 weeks of gestation (n = 70). We measured the stability of these vesicles by quantifying and observing their protein and miRNA contents after the freeze/thawing processes. Exosomes were isolated by differential and buoyant density centrifugation using a sucrose continuous gradient and characterised by their size distribution and morphology using the nanoparticles tracking analysis (NTA; Nanosight™) and electron microscopy (EM), respectively. The total number of exosomes and placenta-derived exosomes were determined by quantifying the immunoreactive exosomal marker, CD63 and a placenta-specific marker (Placental Alkaline Phosphatase PLAP).

Results

These nanoparticles are extraordinarily stable. There is no significant decline in their yield with the freeze/thawing processes or change in their EM morphology. NTA identified the presence of 50–150 nm spherical vesicles in maternal plasma as early as 6 weeks of pregnancy. The number of exosomes in maternal circulation increased significantly (ANOVA, p = 0.002) with the progression of pregnancy (from 6 to 12 weeks). The concentration of placenta-derived exosomes in maternal plasma (i.e. PLAP⁺) increased progressively with gestational age, from 6 weeks 70.6 ± 5.7 pg/ml to 12 weeks 117.5 ± 13.4 pg/ml. Regression analysis showed that weeks is a factor that explains for >70% of the observed variation in plasma exosomal PLAP concentration while the total exosome number only explains 20%.

Conclusions

During normal healthy pregnancy, the number of exosomes present in the maternal plasma increased significantly with gestational age across the first trimester of pregnancy. This study is a baseline that provides an ideal starting point for developing early detection method for women who subsequently develop pregnancy complications, clinically detected during the second trimester. Early detection of women at risk of pregnancy complications would provide an opportunity to develop and evaluate appropriate intervention strategies to limit acute adverse sequel.

Abnormal oxidative stress responses in fibroblasts from preeclampsia infants

Background

Signs of severe oxidative stress are evident in term placentae of infants born to mothers with preeclampsia (PE), but it is unclear whether this is a cause or consequence of the disease. Here fibroblast lines were established from umbilical cords (UC) delivered by mothers who had experienced early onset PE and from controls with the goal of converting these primary cells to induced pluripotent stem cells and ultimately trophoblast. Contrary to expectations, the oxidative stress responses of these non-placental cells from PE infants were more severe than those from controls.

Methods and Findings

Three features suggested that UC-derived fibroblasts from PE infants responded less well to oxidative stressors than controls: 1) While all UC provided outgrowths in 4% O₂, success was significantly lower for PE cords in 20% O₂; 2) PE lines established in 4% O₂ proliferated more slowly than controls when switched to 20% O₂; 3) PE lines were more susceptible to the pro-oxidants diethylmaleate and tert-butylhydroquinone than control lines, but, unlike controls, were not protected by glutathione. Transcriptome profiling revealed only a few genes differentially regulated between PE lines and controls in 4% O₂ conditions. However, a more severely stressed phenotype than controls, particularly in the unfolded protein response, was evident when PE lines were switched suddenly to 20% O₂, thus confirming the greater sensitivity of the PE fibroblasts to acute changes in oxidative stress.

Conclusions

UC fibroblasts derived from PE infants are intrinsically less able to respond to acute oxidative stress than controls, and this phenotype is retained over many cell doublings. Whether the basis of this vulnerability is genetic or epigenetic and how it pertains to trophoblast development remains unclear, but this finding may provide a clue to the basis of the early onset, usually severe, form of PE.

The therapeutic potential of antioxidants, ER chaperones, NO and H2S donors, and statins for treatment of preeclampsia

Preeclampsia is a complex multifactorial disease. Placental oxidative stress, a result of deficient spiral artery remodeling, plays an important role in the pathophysiology of preeclampsia. Antiangiogenic factors secreted from malperfused placenta are instrumental in mediating maternal endothelial dysfunction and consequent symptoms of preeclampsia; the mechanism is likely to involve increased ET-1 secretion and reduced NO bioavailability. Therapeutic interventions so far remain only experimental and there is no established remedy for the treatment of preeclampsia. This review concentrates on the evidence for the therapeutic potential of antioxidants, ER chaperones, NO and H2S donors, and statins. These compounds display pleitropic antioxidant, anti-inflammatory, and pro-angiogenic effects in animal and in vitro studies. Although clinical trials on the use of antioxidant vitamins in pregnancy proved largely unsuccessful, the scope for their use still exists given the beneficial cardioprotective effects of antioxidant-rich Mediterranean diet, periconceptual vitamin use and the synergistic effect of vitamin C and L-arginine. Encouraging clinical evidence exists for the use of NO donors, and a clinical trial is underway testing the effect of statins in treatment of preeclampsia. H2S recently emerged as a novel therapeutic agent for cardiovascular disease, and its beneficial effects were also tested in animal models of preeclampsia. It is risky to prescribe any medication to pregnant women on a large scale, and any future therapeutic intervention has to be well tested and safe. Many of the compounds discussed could be potential candidates.

The timing and duration of hypoxia determine gene expression patterns in cultured human trophoblasts

OBJECTIVE

Exposure of cultured trophoblasts to hypoxia is commonly used to interrogate the molecular mechanisms underlying placental hypoxic injury. We examined the effect of levels, durations, and patterns of hypoxia on gene expression patterns in primary human trophoblasts.

STUDY DESIGN

We exposed primary term human trophoblasts to either standard culture conditions (O(2) = 20%) or to static or alternating levels of oxygen (O(2) = 8%, or O(2) = 0%) either early or late in culture, and analyzed the expression of 34 genes that are known to be regulated in placentas from pregnancies complicated by fetal growth restriction (FGR).

RESULTS

Using multidimensional scale analysis, Euclidean distance, and hierarchical clustering, we found that gene expression patterns in cells exposed to O(2) = 8% were similar to patterns observed in O(2) = 20%, but more distant from patterns in O(2) = 0%. Alternating atmospheric oxygen (8% vs. 0%) yielded intermediate results. Changes in oxygen levels over a longer period had a greater effect on gene expression than short-term changes. Gene expression patterns in cultured trophoblasts did not fully capture expression patterns observed in biopsies from FGR placentas vs. control.

CONCLUSIONS

The level, duration, and patterns of hypoxia are critical in determining trophoblast gene expression, and therefore germane for analysis of trophoblast hypoxic injury.

Doppler analysis and placental nitric oxide synthase expression during fetal growth restriction

OBJECTIVE

To assess placental nitric oxide (NO) metabolism related to changes in the uteroplacental circulation during fetal growth restriction (FGR).

METHODS

The resistance index (RI) from the uterine arteries and pulsatility index (PI) from the umbilical artery were determined by Doppler analysis in 15 patients with FGR and 12 healthy controls, before elective cesarean section. Inducible (iNOS) and endothelial (eNOS) NO synthase expression were measured in placental samples. Immunohistochemistry was performed for iNOS location in the placenta.

RESULTS

During FGR, we observed a significant elevation of iNOS when compared with controls. Conversely, eNOS did not differ between the two groups. A negative correlation with eNOS (r = -0.85) and a positive correlation with iNOS (r = 0.91) was found correlating to umbilical PI. The iNOS proteins were reduced in syncytiotrophoblast cells and increased in endothelium in the FGR group compared to the controls.

CONCLUSIONS

During FGR, placental iNOS expression is significantly increased; this increase possibly represents an adaptive physiological mechanism for overcoming a fetoplacental circulation deficiency.

Gabor Than Award Lecture 2008: pre-eclampsia - from placental oxidative stress to maternal endothelial dysfunction

Pre-eclampsia is the most important complication of human pregnancy worldwide and a major contributor to maternal and fetal morbidity and mortality. Strong evidence exists that generation of placental oxidative stress, secondary to deficient spiral artery remodelling, is a key intermediary event, triggering the secretion of a mixture of placental factors that culminate in an enhanced maternal inflammatory response. Reactive oxygen species (ROS) have been recognised as secondary messengers in intracellular signalling cascades. Experiments studying placental ischaemia-reperfusion in vitro or in vivo during labour provide strong evidence suggesting that oxidative stress and ROS production can activate downstream stress-signalling pathways, p38 and SAPK/JNK MAPK, and the pro-inflammatory NF-kappaB signalling pathway, culminating in the release of inflammatory mediators, apoptotic debris, anti-angiogenic factors and other mediators, which then stimulate a maternal inflammatory reaction that manifests in endothelial dysfunction and the symptoms of pre-eclampsia. Addition of anti-oxidants or blocking the stress or inflammatory pathways in vitro attenuates these effects and opens possibilities for therapeutic intervention.

Doppler examination of uteroplacental circulation in early pregnancy: can it predict adverse outcome?

PURPOSE

To determine whether spectral Doppler measurements obtained from bilateral uterine, arcuate, radial, and spiral arteries in early gestation correlate with adverse pregnancy outcome.

METHODS

One hundred five pregnant women underwent transvaginal Doppler sonographic examination of uteroplacental circulation at 6-12 weeks' gestation. Resistance index (RI) and pulsatility index (PI) of bilateral uterine, arcuate, radial, and spiral arteries were measured. Diameters of gestational sac (GS) and yolk sac, crown-rump length (CRL), GS-CRL difference, and GS/CRL ratio were also recorded. Correlation was made with pregnancy outcome.

RESULTS

Sixteen women developed adverse pregnancy outcome. In these women, right uterine artery PI and RI were significantly higher than in women with normal obstetrical outcome. Spiral artery PI and RI values were also higher, but the difference was not statistically significant. GS-CRL difference, GS/CRL ratio, and yolk sac diameters were significantly lower in this group.

CONCLUSION

Transvaginal Doppler examination can detect hemodynamic changes in uteroplacental circulation associated with subsequent adverse pregnancy outcome.

Physiological adaptation in early human pregnancy: adaptation to balance maternal-fetal demands

After conception, the corpus luteum, placenta, and developing embryo release hormones, growth factors, and other substances into the maternal circulation. These substances trigger a cascade of events that transform the functioning of the maternal cardiovascular, respiratory, and renal systems, which in turn alter the physicochemical determinants of [H+]. Following implantation, maternal adaptations fulfill 4 important functions that support fetal growth. Increased availability of substrates and precursors for fetal-placental metabolism and hormone production is mediated by increases in dietary intake, as well as endocrine changes that increase the availability of glucose and low-density lipoprotein (LDL) cholesterol. Transport capacity is enhanced by increases in cardiac output, facilitating the transport of substrates and precursors to the placenta, and fetal waste products to maternal organs for disposal. Maternal-fetal exchange is regulated by the placenta after 10-12 weeks gestation, but it may occur through histiotrophic mechanisms before this time. Disposal of additional waste products (heat, carbon dioxide, and metabolic byproducts) occurs through peripheral vasodilation and increases in skin blood flow, ventilation, and renal filtration. The maternal physiological adaptations described above must meet the combined demands of maternal exercise and fetal growth. More research is needed to formulate evidence-based guidelines for healthy physical activity in early pregnancy.Key words: maternal adaptation, first trimester, exercise, fetal growth and development, hormones.

The role of ultrasound imaging in diagnosing and investigating early pregnancy failure

The advent of high-resolution transvaginal ultrasound (TVS) has revolutionized our understanding of the pathophysiology and the management of early pregnancy failure. Knowledge of the ultrasound appearances of normal early pregnancy development and a good understanding of its pitfalls are essential for the diagnosis and management of early pregnancy failure. Ultrasound imaging has rapidly replaced all other techniques used to study normal human development in the first trimester, and ultrasound features of the early gestational sac have corroborated anatomical studies showing that the first structures to appear are the celomic cavity and the secondary yolk sac. No single ultrasound measurement of the different anatomical features in the first trimester has been shown to have a high predictive value for determining early pregnancy outcome. Similarly, Doppler studies have failed to demonstrate abnormal blood flow indices in the first-trimester uteroplacental circulation of pregnancies that subsequently end in miscarriage. Ultrasound parameters combined with maternal serum hormone levels, maternal age, smoking habits, obstetric history and the occurrence of vaginal bleeding have all been combined in multivariate analyses, with mixed results. Combined ultrasound and in-vitro experiments have demonstrated that the maternal circulation inside the placenta starts at the periphery at around 9 weeks of gestation and that this is associated with a physiological oxidative stress which could be the trigger for the formation of the placental membranes. Abnormal development of these membranes can result in subchorionic hemorrhage and threatened miscarriage with subsequent long-term consequences such as preterm rupture of the membranes and preterm labor, irrespective of the finding of a hematoma on ultrasound. In both euploid and aneuploid missed miscarriages there is clear ultrasound evidence for excessive entry of maternal blood at a very early stage inside the developing placenta resulting in oxidative stress and subsequent degeneration of villous tissue. The finding of blood flow in the intervillous space in cases of first-trimester miscarriage using color Doppler also appears to be useful in the prediction of success of expectant management. Miscarriages with blood flow within the intervillous space are up to four times more likely to complete with expectant management. TVS is considered the gold standard in the diagnosis and management of incomplete miscarriage. Expectant management of miscarriage, using ultrasound parameters to determine eligibility, could significantly reduce the number of unnecessary evacuations of the retained products of conception, depending on the criteria used.

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).

Uterine glands provide histiotrophic nutrition for the human fetus during the first trimester of pregnancy

Providing adequate nutrition to the fetus is key to a successful pregnancy. The interstitial form of implantation displayed by the human blastocyst is generally associated with early onset of maternal blood flow to the developing placenta, and hence hemotrophic exchange. However, the recent finding that the maternal intraplacental circulation is not fully established until the third month of gestation suggests that human fetal nutrition may be initially histiotrophic. We therefore investigated activity of the uterine glands during early pregnancy. We demonstrate here that these glands remain active until at least wk 10 of pregnancy, and that their secretions are delivered freely into the placental intervillous space. We also demonstrate phagocytic uptake by the placental syncytiotrophoblast of two glycoproteins, the mucin MUC-1 and glycodelin A, synthesized in the maternal glands. Glycodelin was also detected within the epithelium of the secondary yolk sac lining the exocoelomic cavity, indicating that the yolk sac may play an important role in nutrient exchange before vascularisation of the chorionic villi. Our findings demonstrate that the uterine glands are an important source of nutrients during organogenesis, when metabolism is essentially anaerobic.

Comparative developmental anatomy of the murine and human definitive placentae

The placenta of eutherian mammals is a remarkable biological structure. It is composed of both zygote-derived and maternal cells, and mediates the complex interactions between the mother and the fetus that are necessary for fetal growth and survival. While the genetic basis of human placental development and function is largely unknown, its understanding is of immense clinical importance because placentopathies of unknown genetic aetiology are thought to be the cause of many types of pregnancy complications including unexplained miscarriage and intrauterine growth retardation. The mouse is the best-studied mammalian experimental genetic model system and research is not restricted by the inherent ethical and practical limitations associated with the human. As a result, knowledge about the genetic control of mouse placental development has expanded greatly in recent years. In order for this to be of benefit to medical practice, extrapolations from murine to human placentation have to be made. However, comprehensive comparisons of the placentae of these two species are rare. This review therefore compares the developmental anatomy of the placenta between humans and mice with emphasis on structures and cell types that might be analogous between the two species. This could be of particular benefit to mouse developmental geneticists who study placental development and have an interest in the possible clinical implications of their work.

Nutrition of the human fetus during the first trimester--a review

In all mammalian species nutrition of the conceptus is initially histiotrophic, with the trophectoderm phagocytosing first oviductal and then uterine secretions. Following implantation and establishment of the chorioallantoic placenta there is a transition to haemotrophic nutrition, with exchange between the maternal and fetal circulations. It has long been assumed that the transition occurs soon after implantation in the human, due to the invasive nature of this process. However, the recent realization that the maternal circulation to the placenta is not fully established until the end of the first trimester casts doubt on the validity of this assumption. There is new evidence that the uterine glands discharge secretions into the intervillous space until at least 8 weeks of pregnancy, and that these are taken up by the syncytiotrophoblast. Also, during early pregnancy selected maternal proteins accumulate within the fluid of the coelomic cavity, from which they may be transported to the fetus by the secondary yolk sac. Histiotrophic nutrition may be advantageous to the fetus during the first trimester as it provides nutrients under a low oxygen concentration, so reducing the risk of free radical mediated damage during the sensitive period of organogenesis. Once this is complete, and fetal oxygen requirements rise, there is a transition to haemotrophic nutrition at the start of the second trimester, when the maternal placental circulation is fully established.

Correlations between serum assays of human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) and pre-eclampsia or intrauterine growth restriction (IUGR) among nulliparas younger than 38 years

OBJECTIVE

To study the relation between serum human chorionic gonadotrophin (hCG) levels measured at 15-18 weeks and gestational disorders, assess their correlation with the artery uteroplacental Doppler (AUD) at 24 weeks among nulliparas, and assess the predictivity of the hCG/hPL (human placental lactogen) ratio for pre-eclampsia.

STUDY DESIGN

Retrospective study of two groups of women younger than 38 years old: one with an elevated serum hCG level (2 MoM (multiples of the median) or more) and a normal fetal karyotype (group A), and the other with a lower hCG level (group B). Within each group, we studied the nulliparas separately (respectively groups AO and BO). We analyzed the double screening, elevated hCG levels with abnormal AUD, for the predicting of hypertensive disorders.

RESULTS

Elevated hCG levels were significantly (p<0.05) more prevalent among women who developed gestational diabetes (groups A and AO) and among nulliparas with pregnancy-induced hypertension and pre-eclampsia (AO). Among nulliparas, the combination of the hCG assay and a subsequent Doppler increased the positive predictive value (PPV) of the assay from 19 to 75%, without reducing its negative predictive value (NPV) for gestational vascular disorders. The hCG/hPL ratio did not improve the predictivity of the hCG assay alone for pre-eclampsia.

CONCLUSIONS

An hCG level of 2 MoM or more at 15-18 weeks identifies a group of women at risk of gestational vascular disorders; it therefore ought to lead to an AUD at 24 weeks. This double screening should be able to define a population of women at risk of developing a hypertensive disorder, who could thus benefit from a preventive treatment, as aspirin.

Onset of maternal arterial blood flow and placental oxidative stress. A possible factor in human early pregnancy failure

The aim was to measure changes in the oxygen tension within the human placenta associated with onset of the maternal arterial circulation at the end of the first trimester of pregnancy, and the impact on placental tissues. Using a multiparameter probe we established that the oxygen tension rises steeply from <20 mmHg at 8 weeks of gestation to >50 mmHg at 12 weeks. This rise coincides with morphological changes in the uterine arteries that allow free flow of maternal blood into the placenta, and is associated with increases in the mRNA concentrations and activities of the antioxidant enzymes catalase, glutathione peroxidase, and manganese and copper/zinc superoxide dismutase within placental tissues. Between 8 to 9 weeks there is a sharp peak of expression of the inducible form of heat shock protein 70, formation of nitrotyrosine residues, and derangement of the mitochondrial cristae within the syncytiotrophoblast. We conclude that a burst of oxidative stress occurs in the normal placenta as the maternal circulation is established. We speculate that this may serve a physiological role in stimulating normal placental differentiation, but may also be a factor in the pathogenesis of pre-eclampsia and early pregnancy failure if antioxidant defenses are depleted.

First trimester umbilical artery pulsatility index in fetuses presenting enlarged nuchal translucency

The aim of this prospective study was to evaluate an umbilical artery pulsatility index (UAPI) in first trimester fetuses who present enlarged nuchal translucency (NT) measurements. UAPI was measured in 121 single fetuses with NT > or =95th centile, from 10+3 to 13+6 weeks (crown-rump length (CRL) > or =38 mm - < or =84 mm). In these fetuses there were 20 trisomy 21, and six other chromosomal abnormalities (three trisomy 18 and three monosomy X). Eighty-nine cases had normal karyotype and delivered a baby without evidence of congenital malformations. Five fetuses with normal karyotype assessed antenatally were excluded from the comparison, because of evidence of congenital malformation. A fetus with normal karyotype that was spontaneously miscarried at 14 weeks' after chorionic villus sampling was also excluded. UAPI of fetuses with enlarged NT was compared with those of 65 singleton fetuses with normal NT and normal karyotype, which were used to establish our terms of reference (5th centile, median and 95th centile). UAPI of 7/20 (35%) Down syndrome and 42/89 (47%) normal karyotype fetuses presenting enlarged NT were above the median, and respectively 2/20 (10%) and 14/89 (15.7%) were above 95th centile of normal NT and normal karyotype fetuses. No significant differences were demonstrated in the UAPI values amongst normal karyotype fetuses with normal NT or normal karyotype fetuses with an enlarged NT or trisomy 21 fetuses with an enlarged NT.

Differential localization of placental extracellular superoxide dismutase as pregnancy progresses

OBJECTIVE

The aim of this study was to determine placental localization and activity of extracellular superoxide dismutase, a nitric oxide modulator, during early gestation and to correlate these characteristics with fetal vascular development.

STUDY DESIGN

First-trimester (n = 10) and second-trimester (n = 10) villi were obtained at elective pregnancy termination. Extracellular superoxide dismutase was localized by means of an immunoperoxidase method. Activity was measured by determining the inhibition of cytochrome c reduction at pH 10 and messenger ribonucleic acid expression by in situ hybridization.

RESULTS

Extracellular superoxide dismutase was intracellular within villous trophoblasts until 17 weeks' gestation, when it relocated to the villous extracellular matrix. Activities were similar between first- and second-trimester villi. In situ hybridization confirmed extracellular superoxide dismutase messenger ribonucleic acid within trophoblasts throughout gestation.

CONCLUSION

Extracellular superoxide dismutase is produced by trophoblasts early in pregnancy, but it remains intracellular until 17 weeks' gestation, which may be related to fetal vascular development.

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.

Umbilical arterial blood flow in the mouse embryo during development and following acutely increased heart rate

In anesthetized, pregnant ICR mice, we measured embryonic umbilical arterial velocity at baseline and during bipolar atrial or ventricular pacing. Pregnant mice were anesthetized with pentobarbital (60 mg/kg intraperitoneal) and ventilation was mechanically supported via a tracheotomy. Embryos were exposed through a mid-line laparotomy and regional hysterotomy. We recorded umbilical velocity using a 1-mm diameter piezoelectric crystal and 20-MHz, pulsed Doppler velocimeter at embryo day (ED) 10.5 (n = 8), 12.5 (n = 10), 13.5 (n = 27), 14.5 (n = 12), and 16.5 (n = 17). We then acutely altered embryonic heart rate in n = 8 ED 13.5 mouse embryos by bipolar atrial and ventricular pacing. Embryonic heart rate in this experimental preparation increased from 123+/-7 to 193+/-11 beats/min from ED 10.5 to 16.5 (p<0.05). Peak instantaneous average velocity increased from 21+/-2 to 55+/-6 mm/s from ED 10.5 to 16.6 (p<0.05), as did stroke volume and blood flow (p<0.05 for each). In contrast to human umbilical arterial velocity profiles, significant forward diastolic flow was not seen at these stages, suggesting higher placental resistance in mice versus humans at comparable developmental time points. As previously noted for the chick embryo, murine embryonic umbilical arterial velocity decreased after atrial pacing and disappeared after ventricular pacing. Thus, we can determine embryonic umbilical blood flow during the overlapping periods of murine cardiac and placental morphogenesis.

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.

Changes in concentration, localization and activity of catalase within the human placenta during early gestation

Using villous tissue from accurately dated gestational age placentae, this study identified significant changes in the protein concentration, enzyme activity and localization of catalase, an enzyme responsible for the intracellular metabolism of hydrogen peroxide, during the first and early second trimester of pregnancy. Enzyme activity was found to increase approximately threefold between weeks 6 and 17, with the greatest increase between 12 and 17 weeks. Immunostaining of tissue sections was supportive of these findings, demonstrating a progressively stronger signal between weeks 6 and 17. Immunostaining also demonstrated that the main cell types expressing catalase were the cytotrophoblast cells as well as a subset of the stromal cells. Between 13-17 weeks gestation, however, it was possible to detect catalase within the syncytiotrophoblast also, although with a much reduced intensity of staining. At the ultrastructural level, immunogold labelling of catalase clearly showed that staining was predominately compartmentalized within peroxisomes, although non-peroxisomal staining was also seen. Immunoreactivity also demonstrated, via morphological identification, that the stromal cells containing detectable levels of catalase were placental macrophages (Hofbauer cells). These results are in agreement with the proposal that the placenta exists in a physiologically low oxygen environment during the early part of gestation. In this environment oxidative activity of the sort resulting in the generation of hydrogen peroxide would presumably be suppressed, thereby limiting the requirement for catalase until oxygen tension begins to rise.

Placental pathophysiology of the twin oligohydramnios-polyhydramnios sequence and the twin-twin transfusion syndrome

Currently accepted sonographic criteria for antenatal diagnosis of twin-twin transfusion (TTT) syndrome include a monochorionic placenta with same-sex twins, marked growth discordance, and oligohydramnios of the growth-retarded twin with coexistent polyhydramnios of the larger twin. Our previous report of nine women fulfilling these criteria, examined using sequential funipuncture of both fetuses, demonstrated inter-twin blood transfusion in only four cases (44 per cent). It was proposed that traditional sonographic criteria actually describe a heterogeneous group of disorders more appropriately described as the twin oligohydramnios-polydramnios sequence (TOPS). True TTT is a subset of this population, the antenatal diagnosis of which requires specific demonstration of transfusion from one fetus (donor) to the other (recipient). In this report, antenatal placental evaluation has been correlated using duplex pulsed-wave Doppler analysis of arterial blood flow velocity with postpartum gross and histopathologic evaluation of the placenta, with special attention to microvasculature. There was a higher incidence of resistance to blood flow, abnormal umbilical cord insertion, and diminished placental microvasculature associated with oligohydramnic growth-retarded (donor) twins when compared with polyhydramnic (recipient) twins. Based on these observations, it is proposed that TTT and TOPS represent asymmetric placental insufficiency resulting from aberrant placentation.

Determination of intervillous flow in early pregnancy

The process of placentation in the macaque has been extensively studied and found to resemble closely that observed in the human. In this model, histopathologically, intervillous flow is anticipated from week 3 post-conception. We set out to document the nature and onset of intervillous flow in the macaque in vivo using colour Doppler imaging (CDI), colour Doppler energy (CDE) and pulsed-wave Doppler (PWD). Pregnant females were assessed between 15-50 days gestation (term = 165 days) with an Acuson 128/XP10 high-resolution ultrasound scanner, using a 7-MHz linear array probe. The placenta, subjacent decidua and myometrium were assessed using CDI and CDE. Specific regions of flow were interrogated using PWD; the resulting flow velocity waveforms were stored and quantified using conventional Doppler indices. B-mode sonography was able to demonstrate the well-defined placental-decidual interface observed in this species; CDI and CDE clearly visualized the uteroplacental vasculature. Spiral arteries were followed to their point of discharge into the intervillous space, and PWD at these sites obtained a characteristic flow velocity waveform. The indices obtained confirmed a flow of low resistance and pulsatility throughout the gestation studied. Flow within the intervillous space was noted from day 20 of gestation.

Maternal circulation in the first-trimester human placenta--myth or reality?

The classic theory of development of the uteroplacental and intervillous circulation determined that maternal blood enters the intervillous space in high-pressure streams from the early first trimester. This theory has recently been challenged and our hypothesis to be presented is that the intervillous circulation is not fully established until the end of the first trimester. Ex vivo studies of hysterectomy specimens have demonstrated that trophoblastic plugs obstruct blood flow into the intervillous space in early pregnancy and only at 12 to 13 weeks do these plugs become loose and allow for continuous maternal blood flow into the intervillous space. This concept is supported by many other experimental findings. In complicated early pregnancies the uteroplacental circulation demonstrates flow characteristics that are strikingly different from those of normal early pregnancies. In abnormal pregnancies increased flow within the intervillous space is demonstrated by color Doppler imaging. Our hypothesis supports other studies that have shown that the embryo favors an environment low in oxygen during early development and that oxygen levels in placental tissue are low in the early first trimester. The classic drawing of placental circulations is based on second- and third-trimester studies, and its applicability to the early first trimester should be revisited because we will show that new data support the hypothesis that the development of the early intervillous circulation is a progressive phenomenon.

Activation and dimerization of type III nitric oxide synthase by submicromolar concentrations of tetrahydrobiopterin in microsomal preparations from human primordial placenta

We have found in a previous study that 5-50 microM tetrahydrobiopterin (BH4) stimulated 1.2-2.5-fold Ca(2+)-dependent nitric-oxide synthase (NOS) activity in homogenates prepared from primordial human placentae. Now we report on the dramatic, about sixfold, activating effect of BH4 on this activity measured in microsomal preparations. Firstly, both in the absence and presence of BH4, arginine bound to kinetically homogeneous sites, with no significant change between the apparent KM values for arginine (3.12 +/- 1.99 microM and 2.06 +/- 1.13 microM in the absence and presence of 50 microM BH4 respectively, mean +/- s.d., n = 3). On the other hand, the Vmax values measured in different pools of placenta tissue varied between 2.5-7.55 (no BH4 added) and 13.3-58.5 (with BH4 added) pmol/min/mg protein. Secondly, the microsomal preparations responded sensitively to BH4 addition. A dose-response study indicated that as low as 79 nM final BH4 concentration stimulated NOS activity half-maximally, and 1 microM BH4 resulted in an almost maximal effect. Thirdly, immunoblot analysis combined with laser densitometric evaluation demonstrated that BH4 efficiently promoted the aggregation of microsomal NOS type III isozyme into a protein having the characteristics (electrophoretic mobility, resistance of SDS) of the dimeric form. Half-maximal dimerizing activity was reached at 148 +/- 33 nM BH4 (mean +/- s.d., n = 3), whereas 1 microM BH4 led to almost, maximal aggregation of monomers. This is the first time that BH4-induced dimerization of a NOS type III isoform has been demonstrated. Considering that human placenta predominantly expresses NOS type III isoform and BH4 concentration in this tissue is 207 +/- 87 nM, the present results strongly suggest that the dimerizing effect of BH4 is a crucial physiological mechanism for the assembly of active Ca(2+)-dependent NOS in the human primordial placenta.

Nitric oxide synthase in human placenta and umbilical cord from normal, intrauterine growth-retarded and pre-eclamptic pregnancies

1. It has been suggested that a deficiency of nitric oxide (NO) may explain many of the pathophysiological features of pre-eclampsia (PE) and intra-uterine (foetal) growth retardation (IUGR). To elucidate further the role of NO in the pathophysiology of pregnancy we have determined the relative amount and activity of NO synthase (NOS) in first trimester and normal-term placental tissues, as well as in the placenta and umbilical cord in pregnancies complicated by PE and IUGR, using NG-nitro-L-[2,3,4,5(-3)H]-arginine ([3H]-L-NOARG) binding, quantitative in vitro autoradiography, [3H]-arginine to [3H]-citrulline conversion and Western blotting. 2. Specific, high affinity (KD = 38 nM) [3H]-L-NOARG binding was demonstrated in the villous trophoblast of normal-term placentae. Binding was calcium-independent, stereoselective and exhibited a rank order of inhibition by NOS inhibitors and substrate (L-NOARG > or = L-NMMA > or = 7-NI > L-NAME > L-Arg > or = L-NIO > ADMA). 3. [3H]-L-NOARG binding density and NOS activity were both significantly greater in placental tissues from first trimester and PE or IUGR complicated pregnancies compared to normal-term placentae. 4. Western blotting, using an endothelial NOS peptide antiserum, demonstrated a approximately 140 KDa protein band in placental extracts and indicated that the amount of immunoreactive material was significantly greater in first trimester compared to normal-term placentae. 5. Specific [3H]-L-NOARG binding was also localized to the endothelial lining of umbilical arteries and veins, binding density being greater in the artery than the vein. [3H]-L-NOARG binding to the umbilical artery endothelium was significantly lower in PE and IUGR complicated pregnancies compared to normal-term controls. 6. The role of trophoblast-derived NO in human placental pathophysiology remains to be established, but differences in the amount of placental [3H]-L-NOARG binding, NOS activity and immunoreactive material indicate that expression of NOS in the villous trophoblast falls during pregnancy. Conversely, the apparent reduction in NOS in the umbilical artery endothelium in PE and IUGR complicated pregnancies may be indicative of endothelial dysfunction.