Tissue factor-dependent blood coagulation is enhanced following delivery irrespective of the mode of delivery

Women with severe postpartum hemorrhage have a decreased endogenous thrombin potential before delivery

BACKGROUND

Severe postpartum hemorrhage (PPH), defined as a blood loss ≥1000 mL, is associated with maternal morbidity and mortality.

OBJECTIVES

We aimed at characterizing coagulation properties of predelivery plasmas from pregnant women with thrombin generation assay and hemostatic biomarkers (plasminogen activator inhibitor-1, tissue factor [TF], and thrombomodulin).

METHODS

A nested case-control study was conducted within the "Study of Biological Determinants of Bleeding Postpartum," a French prospective cohort study, in order to compare women with severe PPH (cases) and controls matched for age, body mass index, term, and mode of delivery. Plasma was collected at entry in the delivery room, and blood loss was measured objectively. The predelivery endogenous thrombin generation potential (ETP) was measured in plasma using calibrated automated thrombinography and low TF concentration. Hemostatic biomarkers were measured using ELISA kits.

RESULTS

A total of 142 women (71 cases and 71 controls) were investigated. There was no difference in the median lag phase, thrombin peak, and time to peak between cases and controls. However, median predelivery ETP was lower in cases than in controls (2170 vs 2408 nM.min, P < .0001), independently of mode of delivery and PPH etiology. Median plasminogen activator inhibitor-1 and TF levels were higher in cases compared with controls (107.4 vs 68.1 ng/mL, P = .0003; 34.4 vs 27.4 pg/mL, P = .007), whereas thrombomodulin levels did not differ between the 2 groups.

CONCLUSION

Among thrombin generation assay parameters, predelivery ETP levels may have a predictive value for severe PPH.

Thrombosis in Pregnant Women with Hemolytic Anemia

Hemolytic anemias are a group of uncommon disorders affecting both genders, frequently occurring at the reproductive age. While a link between hemolysis and hypercoagulability has been suggested based on the elucidation of certain involved pathophysiological mechanisms, the extent of thrombotic risk in pregnant women with hemolytic anemia remains debatable. Due to the paucity of pregnancy-related data, risk assessment of gestations in women with hemolytic anemia is complicated. This review will highlight the latest advances in the diagnosis and management of these challenging disorders in pregnancy.

Tissue Factor Pathway Inhibitors as Potential Targets for Understanding the Pathophysiology of Preeclampsia

BACKGROUND

Preeclampsia is a hypertensive disorder of pregnancy that causes maternal and perinatal morbidity and mortality worldwide. Preeclampsia is associated with complex abnormalities of the coagulation and fibrinolytic system. Tissue factor (TF) is involved in the hemostatic system during pregnancy, while the Tissue Factor Pathway Inhibitor (TFPI) is a major physiological inhibitor of the TF-initiated coagulation cascade. The imbalance in hemostatic mechanisms may lead to a hypercoagulable state, but prior research has not comprehensively investigated the roles of TFPI1 and TFPI2 in preeclamptic patients. In this review, we summarize our current understanding of the biological functions of TFPI1 and TFPI2 and discuss future directions in preeclampsia research.

METHODS

A literature search was performed from inception to 30 June 2022 in the PubMed and Google Scholar databases.

RESULTS

TFPI1 and TFPI2 are homologues with different protease inhibitory activities in the coagulation and fibrinolysis system. TFPI1 is an essential physiological inhibitor of the TF-initiated extrinsic pathway of coagulation. On the other hand, TFPI2 inhibits plasmin-mediated fibrinolysis and exerts antifibrinolytic activity. It also inhibits plasmin-mediated inactivation of clotting factors and maintains a hypercoagulable state. Furthermore, in contrast to TFPI1, TFPI2 suppresses trophoblast cell proliferation and invasion and promotes cell apoptosis. TFPI1 and TFPI2 may play important roles in regulating the coagulation and fibrinolytic system and trophoblast invasion to establish and maintain successful pregnancies. Concentrations of TF, TFPI1, and TFPI2 in maternal blood and placental tissue are significantly altered in preeclamptic women compared to normal pregnancies.

CONCLUSIONS

TFPI protein family may affect both the anticoagulant (i.e., TFPI1) and antifibrinolytic/procoagulant (i.e., TFPI2) systems. TFPI1 and TFPI2 may function as new predictive biomarkers for preeclampsia and navigate precision therapy.

Proteomic and miRNA Profiles of Exosomes Derived from Myometrial Tissue in Laboring Women

Myometrial contraction is essential for successful delivery. Recent studies have highlighted the vital roles of tissue-derived exosomes in disease diagnostic, prognostic, and therapeutic applications; however, the characteristics of uterine myometrium-derived exosomes are unclear. Here, we successfully isolated exosomes from myometrial tissues, human myometrial smooth muscle cells (HMSMCs), and human umbilical vein endothelial cells (HUVECs), then performed quantitative liquid chromatography-tandem mass spectrometry and miRNA sequencing to investigate the cargo of the exosomes. Fifty-two proteins and five miRNAs were differentially expressed (DE) in term non-labor and term labor myometrium-derived exosomes. Among them, seven proteins (SERPINE1, THBS1, MGAT1, VIM, FGB, FGG, and VWF) were differentially expressed both in the myometrial exosomes and tissues, three miRNAs (miR-363-3p, miR-203a-3p, and miR-205-5p) target 13 DE genes. The top three miRNA derived from HMSMCs (miR-125b-1-3p, miR-337-5p, and miR-503-5p) and HUVECs (miR-663a, miR-4463, and miR-3622a-5p) were identified. Two proteins, GJA1 and SLC39A14, exist in female blood exosomes and are highly expressed in HMSMCs exosomes, are also upregulated in the laboring myometrium, which verified increased in laboring blood samples, might be novel potential biomarkers for myometrial activation. The proteomic and miRNA profile of exosomes derived from laboring myometrium revealed some molecules in the exosomes that affect the intercellular communication and the function of the myometrium.

Risk stratification for pregnancy-associated venous thromboembolism: Potential role for global coagulation assays

Risk assessment for venous thromboembolism in pregnancy and the puerperium is currently limited to stratifying clinical surrogate risk factors without high-quality evidence. While the absolute risk of pregnancy-associated venous thromboembolism is low for the vast majority of women, associated morbidity and mortality remains significant. As guidelines for thromboprophylaxis vary widely, some women may be under- or over-anticoagulated, contributing to poor outcomes. New global coagulation assays provide a holistic view of coagulation and may have the potential to detect hypercoagulability in pregnancy, unlike clinically available coagulation assays. However, there are major technical challenges to overcome before global coagulation assays can be realistically proposed as an adjunct to risk assessment for pregnancy-associated venous thromboembolism. This review summarises the literature and controversies in the prediction and prevention of pregnancy-associated venous thromboembolism and outlines the new tools in haematology that may assist in our future understanding of hypercoagulability in pregnancy.

Circulatory Neutrophils Exhibit Enhanced Neutrophil Extracellular Trap Formation in Early Puerperium: NETs at the Nexus of Thrombosis and Immunity

Pregnancy is associated with elevated maternal levels of cell-free DNA of neutrophil extracellular trap (NET) origin, as circulatory neutrophils exhibit increased spontaneous NET formation, mainly driven by G-CSF and finely modulated by sex hormones. The postpartum period, on the other hand, involves physiological alterations consistent with the need for protection against infections and fatal haemorrhage. Our findings indicate that all relevant serum markers of neutrophil degranulation and NET release are substantially augmented postpartum. Neutrophil pro-NETotic activity in vitro is also upregulated particularly in post-delivery neutrophils. Moreover, maternal puerperal neutrophils exhibit a strong pro-NETotic phenotype, associated with increased levels of all key players in the generation of NETs, namely citH3, MPO, NE, and ROS, compared to non-pregnant and pregnant controls. Intriguingly, post-delivery NET formation is independent of G-CSF in contrast to late gestation and complemented by the presence of TF on the NETs, alterations in the platelet activity status, and activation of the coagulation cascade, triggered by circulating microparticles. Taken together, our results reveal the highly pro-NETotic and potentially procoagulant nature of postpartum neutrophils, bridging an overt immune activation with possible harmful thrombotic incidence.

Phosphatidylserine Exposing Extracellular Vesicles in Pre-eclamptic Patients

Background: Pre-eclampsia (P-EC) is associated with systemic inflammation, endothelial dysfunction and hypercoagulability. The role of extracellular vesicles (EVs) in coagulation disturbances affecting the development and severity of P-EC remains elusive. We aimed to evaluate the concentration of EVs expressing phosphatidylserine (PS) and specific markers in relation to the thrombin and fibrin formation as well as fibrin clot properties, in pregnant women with P-EC in comparison to healthy pregnant women of similar gestational age.

Methods: Blood samples of 30 pregnant women diagnosed with P-EC were collected on the morning following admission to hospital and after delivery (mean duration 5 days). The concentration of the PS-exposing EVs (PS+ EVs) from platelets (CD42a⁺, endothelial cells (CD62E⁺), and PS+ EVs expressing tissue factor (TF) and vascular cell adhesion molecule 1 (VCAM-1) were measured by flow cytometry. Further phenotyping of EVs also included expression of PlGF. Markers of maternal haemostasis were correlated with EVs concentration in plasma.

Results: Preeclamptic pregnancy was associated with significantly higher plasma levels of PS+ CD42a⁺ EVs and PS+ VCAM-1⁺ EVs in comparison with normotensive pregnancy. P-EC patients after delivery had markedly elevated concentration of PS+ CD42a⁺ EVs, CD62E⁺ EVs, TF⁺ EVs, and VCAM-1⁺ EVs compared to those before delivery. Inverse correlation was observed between EVs concentrations (PS+, PS+ TF⁺, and PlGF⁺) and parameters of overall haemostatic potential (OHP) and fibrin formation, while PS+ VCAM-1⁺ EVs directly correlated with FVIII activity in plasma.

Conclusion: Increased levels of PS+ EVs subpopulations in P-EC and their association with global haemostatic parameters, as well as with fibrin clot properties may suggest EVs involvement in intravascular fibrin deposition leading to subsequent microcirculation disorders.

Approach to the Evaluation and Treatment of Venous Thromboembolism in Pregnancy

Thrombosis in pregnancy is a major cause of maternal and fetal morbidity and mortality. Risk stratification of venous thromboembolism (VTE) during pregnancy is complex. The hypercoagulability observed in pregnant women can reduce bleeding during childbirth, but may cause thrombosis especially in the presence of additional prothrombotic risk factors such as antiphospholipid antibodies or genetic thrombophilic defects. The availability of large datasets allows for the identification of additional independent risk factors, including assisted reproductive technologies (ARTs), endometriosis, and recurrent pregnancy loss. Data on the risk of VTE linked to COVID-19 in pregnant women are very limited, but suggest that infected pregnant women have an increased risk of VTE. Current guidelines on the prevention and treatment of VTE in pregnancy are based on available, albeit limited, data and mainly present expert opinion. Low-molecular-weight heparins (LMWHs) are the mainstay of anticoagulation to be employed during pregnancy. Administration of LMWH for VTE treatment in pregnancy should be based on the personalized approach, taking into account a weight-based adjusted scheme. During gestation, due to physiological changes, in women at high risk of VTE, monitoring of anti-Xa activity is performed to ensure adequate LMWH dosing. As for the treatment duration for pregnant women with acute VTE, guidelines suggest that anticoagulation should be continued for at least 6 weeks postpartum for a minimum total duration of therapy of 3 months.

Inhibitory effects of amniotic fluid on the activated protein C anticoagulation system in maternal plasma

Pulmonary thromboembolism (PTE) is one of the leading causes of maternal mortality. We previously reported that possible contamination of amniotic fluid (AF) into maternal circulation accelerated thrombin production and activated platelet function in maternal blood through the extrinsic pathway, which may be associated with the high incidence of PTE in early puerperium. However, it remains unclear whether the maternal anticoagulation system, e.g., the activated protein C (APC) pathway, contributes to the hypercoagulable condition induced by AF. Our previous study using an endogenous thrombin potential (ETP)-based assay revealed that sensitivity to APC was reduced during the postpartum first day, i.e., immediately after delivery, when parturients were supposed to be exposed to AF. Our aim is to investigate the susceptibility of maternal plasma to APC when mixed with AF. We collected plasma from 51 pregnant females and mixed with AF as well as APC. APC-sensitivity ratio (APC-sr) was calculated using the ETP-based assay. Addition of AF to maternal plasma showed a significant increase of ETP in the presence of APC. APC-sr was significantly increased, indicating decreased sensitivity to APC, after AF mixture to maternal plasma. The present APC-sr difference with AF contamination was smaller than that we reported previously in venous thromboembolism cases. The inhibitory effects of AF on the APC anticoagulation pathway may contribute, at least partly, to further promotion of thrombin production induced by AF. Combined with other classical thrombophilic risk factors, the present findings support possible involvements of AF exposure in the high incidence of PTE in early puerperium.

To Clot or Not: HELLP Syndrome and Disseminated Intravascular Coagulation in an Eclamptic Patient with Intrauterine Fetal Demise

A 39-year-old G2P1001 female presented from an outside hospital following an eclamptic seizure in the setting of HELLP syndrome. This condition was complicated by intrauterine fetal demise and disseminated intravascular coagulation, which required an emergent cesarean section. We report the work-up and intraoperative and postoperative management of this complex patient with multiple medical needs. We focus on the hemostatic abnormalities in this patient and describe how our management would differ from that of a similar, nonpregnant patient.

Microparticle Release During Normal Cesarean Delivery

Coagulation increases during pregnancy and peaks during parturition. We hypothesized that an increase in microparticle (MP) levels in plasma occurs around the time of placental separation and subsides over several hours. We performed a prospective observational pilot study to investigate plasma MP levels in healthy parturients immediately before and after cesarean delivery. The primary outcome was MP levels at postdelivery time points compared to baseline levels. Samples underwent flow cytometry and staining to determine MP levels. Placental-derived MPs were further characterized for the presence of procoagulant proteins. Placental-derived MPs increased immediately after delivery before returning to baseline in healthy parturients.

Amniotic fluid as a potent activator of blood coagulation and platelet aggregation: Study with rotational thromboelastometry

INTRODUCTION

Pulmonary thromboembolism (PTE) is a leading cause of maternal death and frequently occurs during early puerperium. Amniotic fluid components are frequently observed in the maternal circulation in parturition; however, it currently remains unclear whether amniotic fluid contamination in maternal blood is related to the high incidence of PTE in early postpartum.

OBJECTIVES

To examine the influence of amniotic fluid on blood coagulation and fibrinolysis systems with thromboelastometry.

MATERIALS AND METHODS

Twenty-one pregnant women were recruited. We used whole citrated blood in ROTEM® (Tem Innovations GmbH, Munich, Germany), including the non-activated assay (NATEM), assessments for extrinsic (EXTEM) and intrinsic pathways (INTEM), fibrin polymerization (FIBTEM), and hyperfibrinolysis (APTEM), with amniotic fluid contamination, and measured the clotting time (CT), clot formation time (CFT), alpha, amplitude at 10 min (A10), maximum clot firmness (MCF), and lysis indices at 30 min (LI30) and 60 min (LI60).

RESULTS

Short CT in all assays as well as short CFT, high alpha, and increased A10 and MCF in NATEM were observed with amniotic fluid contamination. A10 and MCF as well as LI30 and LI60 decreased in EXTEM. Decreased LI60 with the mixture of amniotic fluid was not improved by tranexamic acid in APTEM.

CONCLUSIONS

Amniotic fluid accelerated thrombin production and activated platelet aggregation without inducing hyperfibrinolysis in whole blood. The activated tissue factor pathway with amniotic fluid produced soft and fragile clots due to its influence on platelets, which may be associated with, at least partly, the high incidence of PTE in early puerperium, particularly after cesarean section.

Postpartum haemorrhage: prevention and treatment

INTRODUCTION

Postpartum hemorrhage (PPH) is one of the leading causes of maternal death and severe maternal morbidity worldwide and strategies to prevent and treat PPH vary among international authorities. Areas covered: This review seeks to provide a global overview of PPH (incidence, causes, risk factors), prevention (active management of the third stage of labor and prohemostatic agents), treatment (first, second and third-line measures to control PPH), by also underlining recommendations elaborated by international authorities and using algorithms. Expert commentary: When available, oxytocin is considered the drug of first choice for both prevention and treatment of PPH, while peripartum hysterectomy remains the ultimate life-saving procedure if pharmacological and resuscitation measures fail. Nevertheless, the level of evidence for preventing and treating PPH is globally low. The emergency nature of PPH makes randomized controlled trials (RCT) logistically difficult. Population-based observational studies should be encouraged as they can usefully strengthen the evidence base, particularly for components of PPH treatment that are difficult or impossible to assess through RCT.

Disseminated Intravascular Coagulation Syndromes in Obstetrics

Disseminated intravascular coagulation (DIC) is a syndrome that can be initiated by a myriad of medical, surgical, and obstetric disorders. Also known as consumptive coagulopathy, DIC is a common contributor to maternal morbidity and mortality and is associated with up to 25% of maternal deaths. The etiopathogenesis of DIC is complex and currently thought to be initiated by tissue factor or thromboplastin, which is released from trophoblastic or fetal tissue, or maternal decidua or endothelium. Tissue factor activates the coagulation sequence to cause fibrin clotting and its dissolution by the fibrinolysin system. The result of this process can range from mild, clinically insignificant laboratory derangements to marked coagulopathy with bleeding at sites of minimal trauma. Although clinical recognition varies by disease severity, several organizations have attempted to standardize the diagnosis through development of scoring systems. Several important--albeit not necessarily common--obstetric disorders associated with DIC include placental abruption, amniotic fluid embolism, sepsis syndrome, and acute fatty liver of pregnancy. More common disorders include severe preeclampsia, hemolysis, elevated liver enzymes, and low platelet count syndrome, and massive obstetric hemorrhage. Importantly, many of these disorders either cause or are associated with substantive obstetric hemorrhage. Treatment of DIC is centered on two principles. The first is identification and treatment of the underlying disorder. Because many women with consumptive coagulopathy also have massive hemorrhage, the second tenet of treatment is that obstetric complications such as uterine atony or lacerations must be controlled simultaneously with prompt blood and component replacement for a salutary outcome.

Intrapartum anti-disseminated intravascular coagulation therapy leading to successful vaginal delivery following intrauterine fetal death caused by placental abruption: a case report

Introduction

Disseminated intravascular coagulation due to placental abruption with intrauterine fetal death is not uncommon. It can result in increased maternal mortality rates and the need for hysterectomy or greater transfusion volumes if the delivery is not completed within six to eight hours. However, consensus is lacking regarding the delivery approach for cases in which delivery is prolonged.

Case presentation

A 37-year-old Japanese woman was transported to our tertiary center two and a half hours after the onset of labor because of a diagnosis of placental abruption with intrauterine fetal death at 40 weeks and three days’ gestation. On arrival, although severe hypofibrinogenemia was observed, there was no external hemorrhage. Because her cervical canal dilation was good (Bishop score, 7), labor was induced using oxytocin. Anti-disseminated intravascular coagulation therapy was simultaneously started via transfusion. After her hypofibrinogenemia resolved, delivery progressed rapidly, and the fetus was delivered approximately 10 hours after the onset. To reduce postpartum hemorrhage, 6g of fibrinogen concentrate and tranexamic acid, an antifibrinolytic agent, were administered immediately before extraction of the dead fetus and placenta. Although the amount of intrapartum hemorrhage was 1824g, there was no abnormal bleeding after delivery, and our patient was discharged three days later.

Conclusion

In cases of placental abruption complicated with disseminated intravascular coagulation, intrapartum administration of coagulation factors can simultaneously promote effective labor and correct hypofibrinogenemia, enabling minimally invasive vaginal delivery.

Pathogenesis and management of peripartum coagulopathic calamities (disseminated intravascular coagulation and amniotic fluid embolism)

Acute coagulopathic peripartum calamities are relatively rare but contribute importantly to maternal morbidity and mortality in the Western world. Abruptio placenta, amniotic fluid embolism, and retained fetal or placental material may lead to fulminant intravascular activation of coagulation which results in thromboembolic complications and consumption coagulopathy causing severe hemorrhage. The central underlying pathophysiological pathway in the coagulopathy associated with these syndromes is the occurrence of tissue factor, released from the placenta and amniotic fluid, in the circulation, in combination with low levels of physiological anticoagulant factors during pregnancy. The diagnosis of DIC may be made trough conventional composite scoring systems employing routine coagulation tests, whereas for the diagnosis of amniotic fluid embolism measurement of insulin like growth factor binding protein-1 seems promising. Therapy is aimed at removing the precipitating factor combined with supportive adjunctive treatment options.

Thrombin generation post elective caesarean section: effect of low molecular weight heparin

INTRODUCTION

Caesarean section (CS) is a significant risk factor for venous thromboembolism.. Low molecular weight heparin (LMWH) is commonly used for thromboprophylaxis post emergency caesarean delivery. However, no consensus exists regarding LMWH thromboprophylaxis following elective caesarean section. Measures of thrombin formation may indicate the full anticoagulant activity of LMWH in this setting.

MATERIALS AND METHODS

Anti-Xa, tissue factor pathway inhibitor (TFPI), thrombin anti-thrombin complex (TAT) and endogenous thrombin potential (ETP) were measured in twenty healthy women who received 4,500 IU tinzaparin 6 hours post CS (CS1), twenty women who received 4,500 IU tinzaparin at 10-12 hours post delivery (CS2) and twenty women post spontaneous vaginal delivery (SVD).

RESULTS

Prior to initiation of LMWH, TAT levels at 6 hours post delivery were significantly higher in the CS1 and CS2 groups than the SVD group (P<0.002); TAT levels were significantly reduced up to 24 hours post LMWH treatment despite declining anti-Xa levels (P<0.001). In CS1, peak thrombin and ETP were significantly reduced following LMWH prophylaxis (P<0.0001; P<0.002) and reverted to pre-delivery levels 10 hours post LMWH. TFPI levels mirror anti-Xa levels during the 24 hours following LMWH treatment in CS1 group with peak levels coinciding with peak anti-Xa levels 4 hours post injection.

CONCLUSION

In women post caesarean section, anti-Xa levels do not reflect the full anticoagulant effects of LMWH. In-vivo thrombin production (TAT) is effectively reduced even when anti-Xa levels are negligible. LMWH thromboprophylaxis in this healthy cohort of patients appears to have a sustained effect in reducing excess thrombin production post elective caesarean section.

Peripartum pulmonary embolism

Pregnancy is an example of Virchow's triad predisposing to the development of venous thromboembolism (VTE). Specific risk factors for antepartum and postpartum VTE have been identified. The diagnosis of pulmonary embolism in pregnancy is complicated by the physiologic changes of pregnancy as well as physicians' apprehension about ordering radiologic studies during pregnancy because of concerns with fetal well-being. Therapy for VTE is complicated by pregnancy physiology affecting medication pharmacokinetics and bioavailability, and the unpredictable occurrence of labor during therapeutic anticoagulation.

The association between thromboelastographic parameters and total estimated blood loss in patients undergoing elective cesarean delivery

BACKGROUND

In this study, we assessed the relationship between coagulation parameters using kaolin-activated thromboelastography (TEG®) and total estimated blood loss (EBL) in patients undergoing elective cesarean delivery (CD).

METHODS

TEG® parameters were recorded in 52 patients before and after elective CD. Laboratory markers of coagulation (prothrombin time, activated partial thromboplastin time, fibrinogen) were also assessed in a smaller subset (21 patients). Correlation and linear regression analysis was used to assess the relationship among TEG® parameters, relevant clinical variables, and total EBL. Secondary analysis included comparisons of TEG® and coagulation profiles pre-CD versus post-CD.

RESULTS

EBL weakly correlated with percentage change in maximum amplitude (r=0.3; P=0.04) and post-CD maximum rate of thrombus generation (r=0.31; P=0.02). Post-CD values for split point, reaction time, time to maximum rate of thrombin generation, prothrombin time, and activated partial thromboplastin time were significantly increased compared with baseline values (P<0.05). Post-CD α angle, maximum amplitude, total thrombus generation, fibrinogen, and platelet counts were significantly decreased compared with baseline values (P<0.05).

CONCLUSIONS

There is a weak association between clot strength (as assessed by kaolin-activated TEG®) and EBL in patients undergoing elective CD under neuraxial anesthesia, and a modest reduction in the degree of maternal hypercoagulability occurs in the early postpartum period after elective CD.

Local anesthetic use in the pregnant and postpartum patient

The use of systemically absorbed drugs in the gravid and in the lactating patient is of concern to the dentist. This article reviews concerns for the health and safety of the mother, developing fetus, and neonate involving local anesthetics. The available literature on the use of local anesthetics for dentistry in the pregnant and postpartum patient is also reviewed. In addition, the physiology of the pregnant and postpartum woman is discussed because this is essential to understanding potential interplay with local anesthesia and the stress of a dental appointment.