Retrograde aortic isthmus net blood flow and human fetal cardiac function in placental insufficiency

Fetal aortic isthmus Doppler assessment to predict the adverse perinatal outcomes associated with fetal growth restriction: systematic review and meta-analysis

PURPOSE

Fetal growth restriction (FGR) management and delivery planning is based on a multimodal approach. This meta-analysis aimed to evaluate the prognostic accuracies of the aortic isthmus Doppler to predict adverse perinatal outcomes in singleton pregnancies with FGR.

METHODS

PubMed, EMBASE, the Cochrane Library, ClinicalTrials.gov and Google scholar were searched from inception to May 2021, for studies on the prognostic accuracy of anterograde aortic isthmus flow compared with retrograde aortic isthmus flow in singleton pregnancy with FGR. The meta-analysis was registered on PROSPERO and was assessed according to PRISMA and Newcastle-Ottawa Scale. DerSimonian and Laird's random-effect model was used for relative risks, Freeman-Tukey Double Arcsine for pooled estimates and exact method to stabilize variances and CIs. Heterogeneity was quantified using I2 statistics.

RESULTS

A total of 2933 articles were identified through the electronic search, of which 6 studies (involving 240 women) were included. The quality evaluation of studies revealed an overall acceptable score for study group selection and comparability and substantial heterogeneity. The risk of perinatal death was significantly greater in fetuses with retrograde Aortic Isthmus blood flow, with a RR of 5.17 (p value 0.00001). Similarly, the stillbirth rate was found to have a RR of 5.39 (p value 0.00001). Respiratory distress syndrome had a RR of 2.64 (p value = 0.03) in the group of fetuses with retrograde Aortic Isthmus blood flow.

CONCLUSION

Aortic Isthmus Doppler study may add information for FGR management. However, additional clinical trial are required to assess its applicability in clinical practice.

Heart function by M-mode and tissue Doppler in the early neonatal period in neonates with fetal growth restriction

BACKGROUND

Fetal growth restricted (FGR) neonates have increased risk of circulatory compromise due to failure of normal transition of circulation after birth.

AIM

Echocardiographic assessment of heart function in FGR neonates first three days after birth.

STUDY DESIGN

Prospective observational study.

SUBJECTS

FGR- and non-FGR neonates.

OUTCOME MEASURES

M-mode excursions and pulsed-wave tissue Doppler velocities normalised for heart size and E/e' of the atrioventricular plane day one, two and three after birth.

RESULTS

Compared with controls (non-FGR of comparable gestational age, n = 41), late-FGR (gestational age ≥ 32 weeks, n = 21) exhibited higher septal excursion (15.9 (0.6) vs. 14.0 (0.4) %, p = 0.021) (mean (SEM)) and left E/e' (17.3 (1.9) vs.11.5 (1.3), p = 0.019). Relative to day three, indexes on day one were higher for left excursion (21 (6) % higher on day one, p = 0.002), right excursion (12 (5) %, p = 0.025), left e' (15 (7) %, p = 0.049), right a' (18 (6) %, p = 0.001), left E/e' (25 (10) %, p = 0.015) and right E/e' (17 (7) %, p = 0.013), whereas no index changed from day two to day three. Late-FGR had no impact on changes from day one and two to day three. No measurements differed between early-FGR (n = 7) and late-FGR.

CONCLUSIONS

FGR impacted neonatal heart function the early transitional days after birth. Late-FGR hearts had increased septal contraction and reduced left diastolic function compared with controls. The dynamic changes in heart function between first three days were most evident in lateral walls, with similar pattern in late-FGR and non-FGR. Early-FGR and late-FGR exhibited similar heart function.

Evaluación integrada del bienestar en un feto apropiado para la edad gestacional (AGA) e insuficiencia placentaria aguda debido a corioamnionitis histológica: Reporte de caso

Introducción. La insuficiencia vascular útero placentaria aguda es una causa de desenlace fetal adverso en fetos con crecimiento adecuado para la edad gestacional. Caso clínico. Paciente de 24 años, con 37 semanas de edad gestacional acude al Instituto Nacional Materno Perinatal de Lima, Perú, por referir escaso sangrado vía vaginal. En la evaluación clínica, se encontró una PA 90/60 mmHg, altura uterina 32 cm, latidos cardiacos fetales en 152. A la evaluación ecográfica, a 1 hora de la admisión se reportó feto de 2902 gramos (percentil 34 Hadlock), un Perfil Biofísico Fetal 6/8 por movimientos corporales disminuidos, Índice de líquido amniótico 11cm, placenta fúndica posterior grado III, IP Doppler de Arteria Cerebral Media 1.18, IP Doppler de la arteria umbilical 0.56, IP ductus venoso 0.26 e Istmo Aórtico con diástole ausente. La prueba estresante a las 3 horas de la admisión fue reportada en 5 puntos con movimientos fetales disminuidos, variabilidad disminuida y aceleraciones ausentes. Se indicó cesárea de emergencia obteniéndose recién nacido masculino de 2846 gr, talla 47.5 cm, Apgar 8 – 9. Se encontró líquido meconial de aspecto sanguinolento oscuro. Al corte de la placenta, se observó parénquima con infartos vellosos: recientes 10% y antiguos 5%. Vellosidades coriales hipoplásicas con espacios intervellosos amplios e infiltrado inflamatorio agudo en corion y amnios, correspondientes a Corioamnionitis aguda y funisitis aguda en el cordón umbilical. Conclusiones. La vigilancia integrada de fetos AEG permiten detectar a fetos en riesgo de desenlace adverso por una insuficiencia placentaria aguda secundaria a corioamnionitis histológica o subclínica.

The Accelerated Right Ventricular Failure in Fetal Anemia in the Presence of Restrictive Foramen Ovale

Objective: To describe serious hemodynamic changes secondary to anemia in the case of restrictive foramen ovale (FO). Case: A 43-year-old pregnant woman, G4P0030, underwent fetal echocardiography at 35 weeks of gestation and was found to have (1) restrictive FO; (2) poor right ventricular function; (3) unbalanced hemodynamics; (4) fetal anemia (high MCA-PSV and hepatosplenomegaly). Acid-elution test indicated feto-maternal hemorrhage. Cesarean section was performed for postnatal blood transfusion. Nevertheless, the newborn developed heart failure and died after partial blood exchanges. Conclusions: Insights gained from this study are as follows: (1) Restrictive FO in structurally normal hearts can modify fetal response to anemia differently, by unequally distributing blood volume, leading to much more deteriorating right ventricular function. (2) To make decisions for intrauterine or extrauterine treatment in cases of anemia-associated heart failure, several factors must be taken into account such as gestational age, fetal cardiac function, and placental function. Because of the hyperdynamic state of newborns immediately after birth, delivery can deteriorate the compromised heart to irreversible failure. Intrauterine transfusion for a well-prepared heart just before delivery may be the best option since the baby should be well oxygenated at the time of delivery.

Evaluation of fetal foramen ovale blood flow by pulsed Doppler ultrasonography combined with spatiotemporal image correlation : To define the normal reference range of fetal foramen ovale blood volume for each gestational age: a cross-sectional study

Objective

The objective of this study was to determine fetal foramen ovale blood flow utilizing pulsed Doppler combined with spatiotemporal image correlation.

Methods

A cross-sectional study was performed in 440 normal fetuses between 20 and 40 weeks of gestation. In order to calculate foramen ovale blood flow, the foramen ovale flow velocity–time integral was obtained by pulsed Doppler ultrasonography, and the foramen ovale area was measured by using spatiotemporal image correlation rendering mode. Foramen ovale blood flow was calculated as the product of the foramen ovale area and the velocity–time integral.

Results

Gestational age-specific reference ranges are given for the absolute blood flow (ml/min) of foramen ovale, showing an exponential increase from 20 to 30 weeks of gestation, and a flat growth trend during the last trimester, while the weight-indexed flow (ml/min/kg) of foramen ovale decreased significantly. The median weight-indexed foramen ovale blood flow was 320.82 ml/min/kg (mean 319.1 ml/min/kg; SD 106.33 ml/min/kg).

Conclusions

The reference range for fetal foramen ovale blood flow was determined from 20 to 40 weeks of gestation. The present data show that the volume of foramen ovale blood flow might have a limited capacity to increase during the last trimester.

Doppler studies of placental function

Placental-associated diseases account for most cases of adverse perinatal outcome in developing countries. Doppler evaluation has been incorporated as a predictive parameter at early pregnancy for high-risk placental disease, in the diagnosis and management of those fetuses with impaired intrauterine growth and for the evaluation of fetal wellbeing in those high-risk pregnancies. Uterine Doppler at second trimester predicts most instances of early-onset preeclampsia and intrauterine growth restriction. However, the growing evidence of an effective early propylactic strategy, has turned Uterine Doppler an essential parameter to be included in first trimester predictive algorithms. Umbilical artery Doppler helps in the identification of small-for-gestational-age fetuses at higher risk, and is one of the essential vessels in the assessment of fetal hypoxia impairment, especially in the early cases. It helps in the decision timing for ending the pregnancy improving thus perinatal outcomes. Moreover, in high-risk pregnancies, umbilical artery Doppler has demonstrated to reduce the risk of perinatal deaths and the risk of obstetric interventions. On the other hand, middle cerebral artery Doppler reflects fetal adaptation to hypoxia, and with the cerebroplacental ratio, they improve the detection of fetuses a high risk of adverse perinatal outcome, mostly of those late small fetuses, where most instances of adverse outcome occur in fetuses with normal umbilical artery. Ductus venosous Doppler waveform is a surrogate parameter of the fetal base-acid status. Its use has demonstrated to improve perinatal outcomes, mainly reducing the risk of fetal intrauterine death. Alone or in combination with computerized CTG, it helps tailoring the best moment to end the pregnancy among early cases.

Fetal cardiovascular hemodynamics in type 1 diabetic pregnancies at near-term gestation

INTRODUCTION

Poor glycemic control in maternal type 1 diabetes mellitus during pregnancy can affect fetal cardiac and placental function. However, studies concerning fetal central hemodynamics have revealed conflicting results. We hypothesized that in pregnancies complicated by maternal type 1 diabetes, fetal cardiovascular and placental hemodynamics are comparable to the control fetuses at near-term gestation. In addition, we investigated the relation between newborn serum biomarkers of cardiac function and fetal cardiovascular and placental hemodynamics. Furthermore, we studied whether maternal diabetes is associated with placental inflammation.

MATERIAL AND METHODS

In this prospective case-control study, fetal central and peripheral hemodynamics were assessed by ultrasonography in 33 women with type 1 diabetes and in 67 controls with singleton pregnancies between 34⁺² and 40⁺² gestational weeks. Newborn umbilical cord serum was collected to analyze cardiac natriuretic peptides (atrial and B-type natriuretic peptides) and troponin T concentrations. Placental tissue samples were obtained for cytokine analyses.

RESULTS

Fetal ventricular wall thicknesses were greater and weight-adjusted stroke volumes and cardiac outputs were lower in the type 1 diabetes group than in the control group. Pulsatility in the aortic isthmus and inferior vena cava blood flow velocity waveforms was greater in the type 1 diabetes group fetuses than in the controls. A positive correlation was found between branch pulmonary artery and aortic isthmus pulsatility index values. Umbilical artery pulsatility indices were comparable between the groups. Umbilical cord serum natriuretic peptide and troponin T concentrations were elevated in the type 1 diabetes fetuses. These cardiac biomarkers correlated significantly with cardiovascular hemodynamics. Placental cytokine levels were not different between the groups.

CONCLUSIONS

In maternal type 1 diabetes pregnancies, fetal cardiovascular hemodynamics is impaired. Maternal type 1 diabetes does not seem to alter placental vascular impedance or induce placental inflammation.

Aortic Isthmus Doppler Velocimetry in Fetuses with Intrauterine Growth Restriction: A Literature Review

Intrauterine growth restriction (IUGR) is associated with poor perinatal prognosis and a higher risk of stillbirth, neonatal death, and cerebral palsy. Its detection and the evaluation of its severity by new Doppler velocimetric parameters, such as aortic isthmus (AoI), are of great relevance for obstetrical practice. The AoI is a vascular segment that represents a point of communication between the right and left fetal circulations. It is considered to be a functional arterial shunt that reflects the relationship between the systemic and cerebral impedances, and has recently been proposed as a tool to detect the status of hemodynamic balance and prognosis of IUGR in fetuses. In the present review, we noticed that in healthy fetuses, the AoI net flow is always antegrade, but in fetuses with IUGR the deterioration of placental function leads to progressive reduction in its flow until it becomes mostly retrograde; this point is associated with a drastic reduction in oxygen delivery to the brain. The more impaired the AoI flow is, the greater is the risk of impairment in the Doppler velocimetry of other vessels; and the alterations of the AoI Doppler seem to precede other indicators of severe hypoxemia. Although there seems to be an association between the presence of retrograde flow in the AoI and the risk of long-term neurologic disability, its role in the prediction of perinatal morbi-mortality remains unclear. The AoI Doppler seems to be a promising tool in the management of fetuses with IUGR, but more studies are needed to investigate its employment in clinical practice.

Prenatal Identification of Restrictive and Non-restrictive Ventricular Septal Defects Based on End-Systolic Flow Patterns in the Fetal Aortic Isthmus

Fetuses with large ventricular septal defects (VSDs) must be closely monitored during the perinatal period. Intrauterine assessment of size of septal defects with bidimensional echocardiography are unreliable. The objective of the present study is to document the contribution of flow pattern analysis in the fetal aortic isthmus for prenatal identification of large non-restrictive VSDs requiring immediate postnatal attention. We conducted a cross-sectional retrospective study of Doppler recordings from patients referred to our Fetal Cardiology Unit and diagnosed with one or multiple VSDs from January 2006 to November 2015. Three groups were defined: (1) large non-restrictive VSDs (n = 11) with postnatal cardiac failure (2) small restrictive VSDs (n = 28) asymptomatic, and (3) absence of cardiac abnormality (n = 66). The Isthmic end-Systolic Index (ISI) was computed to quantify aortic isthmus flow and compared between the three groups. Fetuses with restrictive VSD and control group showed similar ISI: stable at 0.20 ± 0.01 up to 27 weeks of gestation and dropping later due to the fall of end-systolic velocities in the aortic isthmus. By 35 weeks, a brief end-systolic retrograde flow was present, associated with a further fall of ISI down to -0.26 ± 0.05. In contrast, ISI of fetuses with large non-restrictive VSDs were unchanged throughout gestation (0.18 ± 0.06), becoming significantly higher during the last weeks of gestation compared to the two other groups (p < 0.001). In fetuses with VSDs, the ISI measurement from the aortic isthmus Doppler flow during the second half of gestation is a reliable predictor of a large non-restrictive defect with risk of major postnatal clinical impact.

Prognostic value of the aortic isthmus Doppler assessment on late onset fetal growth restriction

Background As conflicting results have been reported about the association of reversed flow on the aortic isthmus (AoI) and adverse perinatal results in fetal growth restriction (FGR), we aim to compare perinatal outcomes (including tolerance to labor induction) of late-onset FGR between those with anterograde and reversed AoI flow. Methods This was an observational retrospective cohort study on 148 singleton gestations diagnosed with late-onset FGR (diagnosis ≥32+0 weeks), with an estimated fetal weight (EFW) <10th centile and mild fetal Doppler alteration: umbilical artery (UA) pulsatility index (PI) >95th centile, middle cerebral artery (MCA)-PI <5th centile or cerebral-placental ratio <5th centile. Anterograde AoI flow was present in n=79 and reversed AoI flow in n=69. Delivery was recommended from 37 weeks in both groups. Perinatal results were compared between the groups. Results The global percentage of vaginal delivery of fetuses with anterograde and reversed blood flow was 55.7% vs. 66.7% (P=0.18) and the percentage of cesarean section (C-section) for non-reassuring fetal status was 12.7% vs. 15.9% (P=0.29), respectively. When evaluating those that underwent labor induction, the vaginal delivery rate was 67.9% vs. 77.2% (P=0.17), respectively. There were no significant differences regarding any other perinatal variables and there were no cases of severe morbidity or mortality. Conclusion We observed that the presence of reversed AoI flow does not worsen perinatal outcomes on fetuses with late-onset growth restriction with mild Doppler alterations. Attempt of labor induction is feasible in these fetuses regardless of the direction of AoI flow.

An integrated approach to fetal growth restriction

Fetal growth restriction (FGR) is among the most common complications of pregnancy. FGR is associated with placental insufficiency and poor perinatal outcomes. Clinical management is challenging because of variability in clinical presentation. Fetal smallness (estimated fetal weight <10th centile for gestational age) remains the best clinical surrogate for FGR. However, it is commonly accepted that not all forms of fetal smallness represent true FGR. In a significant subset of small fetuses, there is no evidence of placental involvement, perinatal outcomes are nearly normal, and they are clinically referred to as "only" small for gestational age (SGA). Doppler may improve the clinical management of FGR; however, the need to use several parameters sometimes results in a number of combinations that may render interpretation challenging when translating into clinical decisions. We propose that the management of FGR can be simplified using a sequential approach based on three steps: (1) identification of the "small fetus," (2) differentiation between FGR and SGA, and (3) timing of delivery according to a protocol based on stages of fetal deterioration.

Early onset fetal growth restriction

Fetal growth restriction remains a challenging entity with significant variations in clinical practice around the world. The different etiopathogenesis of early and late fetal growth restriction with their distinct progression of fetal severity and outcomes, compounded by doctors and patient anxiety adds to the quandary involving its management. This review summarises the literature around diagnosing and monitoring early onset fetal growth restriction (early onset FGR) with special emphasis on optimal timing of delivery as guided by recent research advances.

Intrauterine Growth Restriction: Antenatal and Postnatal Aspects

Intrauterine growth restriction (IUGR), a condition that occurs due to various reasons, is an important cause of fetal and neonatal morbidity and mortality. It has been defined as a rate of fetal growth that is less than normal in light of the growth potential of that specific infant. Usually, IUGR and small for gestational age (SGA) are used interchangeably in literature, even though there exist minute differences between them. SGA has been defined as having birth weight less than two standard deviations below the mean or less than the 10th percentile of a population-specific birth weight for specific gestational age. These infants have many acute neonatal problems that include perinatal asphyxia, hypothermia, hypoglycemia, and polycythemia. The likely long-term complications that are prone to develop when IUGR infants grow up includes growth retardation, major and subtle neurodevelopmental handicaps, and developmental origin of health and disease. In this review, we have covered various antenatal and postnatal aspects of IUGR.

The Aortic Isthmus: A Significant yet Underexplored Watershed of the Fetal Circulation

The aortic isthmus (AoI) is a unique fetal watershed with a waveform reflecting its complex haemodynamic physiology. The systolic component represents left and right ventricular systolic ejection, and the diastolic component represents comparative downstream vascular impedance between the brachiocephalic and subdiaphragmatic fetal circulations. Several indices have been devised to quantify different components of the waveform, including the pulsatility index, resistance index, isthmic flow index, and recently the isthmic systolic index. There have been promising preliminary studies applying these indices to both cardiac (congenital) and extracardiac pathologies, including intrauterine growth restriction and twin-twin transfusion syndrome. However, the waveform's multifactorial origin has proven to be challenging, and the difficulty in separating various components of the waveform could explain that AoI evaluation does not have a clear clinical utility. Further research is underway to realise the full potential of this vessel in fetal cardiac and haemodynamically compromised pathological conditions. In this review article we outline the physiological origin of this Doppler waveform, describe in detail the various published indices, summarise the published literature to date, and finally outline potential future research and hopefully clinical applications.

Effects of fetal cardiac anomalies on ductus venosus and aortic isthmus doppler profiles

PURPOSE

To demonstrate the blood flow profiles of fetuses with cardiac anomalies at the level of Ductus venosus (DV) and Aortic isthmus (AI) to evaluate the effects of fetal cardiac anomalies on these profiles, and how these profile changes contribute to cardiac anomaly screening studies as a marker.

METHODS

DV and AI doppler studies were applied to 64 singleton pregnant women with fetal cardiac anomalies and 74 pregnant women with healthy fetuses. DV-PVIV (peak velocity index for veins) for DV and IFI (isthmic flow index) for AI were used.

RESULTS

DV doppler studies in fetuses with cardiac anomalies and healthy fetuses did not show statistically significant difference. But the results of the AI doppler studies had statistically significant difference in the fetal cardiac anomaly group with the exception of cases with dilatation and regurgitation. When right-sided heart anomaly and the remaining cases were compared with the control groups, AI doppler results also showed lower IFI values.

CONCLUSIONS

DV doppler studies in the second or third trimester may not be suitable as a screening test for congenital heart disease, but AI doppler studies might be considered as a supporting parameter. But further studies are needed for routine clinical use.

Fetal-maternal interface impedance parallels local NADPH oxidase related superoxide production

Blood flow assessment employing Doppler techniques is a useful procedure in pregnancy evaluation, as it may predict pregnancy disorders coursing with increased uterine vascular impedance, as pre-eclampsia. While the local causes are unknown, emphasis has been put on reactive oxygen species (ROS) excessive production. As NADPH oxidase (NOX) is a ROS generator, it is hypothesized that combining Doppler assessment with NOX activity might provide useful knowledge on placental bed disorders underlying mechanisms. A prospective longitudinal study was performed in 19 normal course, singleton pregnancies. Fetal aortic isthmus (AoI) and maternal uterine arteries (UtA) pulsatility index (PI) were recorded at two time points: 20-22 and 40-41 weeks, just before elective Cesarean section. In addition, placenta and placental bed biopsies were performed immediately after fetal extraction. NOX activity was evaluated using a dihydroethidium-based fluorescence method and associations to PI values were studied with Spearman correlations. A clustering of pregnancies coursing with higher and lower PI values was shown, which correlated strongly with placental bed NOX activity, but less consistently with placental tissue. The study provides evidence favoring that placental bed NOX activity parallels UtA PI enhancement and suggests that an excess in oxidation underlies the development of pregnancy disorders coursing with enhanced UtA impedance.

The (Pulsed-Wave) Doppler Fetal Myocardial Performance Index: Technical Challenges, Clinical Applications and Future Research

Functional cardiovascular assessment is becoming an increasingly important tool in the study of fetal pathology. The myocardial performance index (MPI) is a parameter measuring global myocardial function. Since its introduction, several studies have proposed methods to improve its reproducibility and have constructed normative reference ranges. Fetal heart evaluation using the MPI is technically challenging, requiring specific training and expertise, and a consensus has yet to be reached on the method of delineating the time periods used to calculate the index. Despite these limitations, it has been shown to be a useful and highly sensitive parameter of dysfunction in a number of fetal pathologies. Further research is warranted into the effect of pathology on MPI, parameters of unilateral cardiac strain that utilise MPI, and automation of the MPI to encourage incorporation of the MPI as a useful tool in clinical practice.

Reference ranges for the pulsatility index of the fetal aortic isthmus in singleton and twin pregnancies

OBJECTIVES

The purpose of this study was to estimate reference ranges for the pulsatility index (PI) of the fetal aortic isthmus in uncomplicated singleton and twin pregnancies during the second half of pregnancy.

METHODS

We conducted a cross-sectional observational study involving 543 healthy fetuses: 361 singleton pregnancies and 182 twin pregnancies between 19 and 36 weeks' gestation. The aortic isthmus PI was measured in 2 sonographic planes: the longitudinal aortic arch view and the 3-vessel and trachea view. We evaluated the reproducibility of aortic isthmus PI measurements between these planes by calculating intraclass correlation coefficients and limits of agreement. Scans were performed by 2 physicians, and intraobserver agreement was also measured. Regression analysis was used to estimate gestational age reference values for the aortic isthmus PI.

RESULTS

The aortic isthmus PI was significantly correlated with gestational age in singletons and twins during the second half of pregnancy (P < .01). We did not find significant differences between reference ranges in singletons and twins or between the sonographic views.

CONCLUSIONS

This study offers reference ranges for the aortic isthmus PI during the second half of gestation in singleton and twin pregnancies. Mean aortic isthmus PI values were similar in both types of gestations as well as both sonographic views. The aortic isthmus PI may be reliably obtained from either sonographic view.

Fetal ventricular interactions and wall mechanics during ductus arteriosus occlusion in a sheep model

We investigated the effect of fetal sheep ductus arteriosus occlusion (DO) on the distribution of cardiac output and left and right ventricular function by tissue and pulsed Doppler at baseline; after 15 and 60 min of DO induced with a vascular occluder; and 15 min after release of DO. Ductal occlusion decreased fetal pO2. Mean left ventricular output increased (p < 0.001) from 725 to 1013 mL/min, and right ventricular (1185 mL/min vs. 552 mL/min) and systemic (1757 mL/min vs. 1013 mL/min) cardiac outputs fell (p < 0.001) after 15 min of DO, compared with baseline. Pulmonary vascular impedance decreased and volume blood flow increased more than threefold during DO, whereas foramen ovale volume blood flow remained unchanged. Left ventricular systolic function was unaffected, whereas isovolumic relaxation velocity deceleration decreased. Right ventricular functional indices remained unchanged. We conclude that DO increased pulmonary volume blood flow, not foramen ovale volume blood flow. Left ventricular output increased, although not as much as right ventricular output fell, resulting in decreased systemic cardiac output. During DO, left ventricular function exhibited diminished relaxation.

Doppler assessment of fetal aortic isthmus flow in twin

Objective

The purpose of this study was to investigate the aortic isthmus (AoI) flow difference between larger fetus and smaller fetus of twin; and to evaluate the predictive value of early diagnosis of hemodynamic change in twin growth.

Methods

This prospective study on 49 pairs of twin fetuses was performed to obtain AoI blood flow data. Cases with structural or chromosomal abnormalities and co-twin death were excluded. The interval from examination to delivery was within 4 weeks and 3 cases over 4 weeks interval were re-examined. Assessment of fetal AoI Doppler parameters were peak systolic velocity (PSV), end-diastolic velocity, times-averaged maximum velocities, pulsatility index (PI), and resistance index (RI). According to the direction of the diastolic flow in the AoI, antegrade and retrograde flow were made and was used to analyze the perinatal outcomes of each fetus. The predictive value of AoI Doppler parameters in predicting fetal growth was obtained by using ANOVA and logistic regression analysis of quantitative variables in each fetus of twins.

Results

There were significant differences in the gestational weeks at delivery, birth weight and the incidence of growth discordance over 20% or more between monochorionic twin and dichorionic twin. The AoI PI and RI were significantly higher in smaller fetus than in larger regardless of chorionicity. Retrograde flow was noted in 8 of 98 cases (8.2%) and the only one case was of the larger fetus and the others were smaller fetuses of twin. Significant correlations were found between the AoI PI and birthweight (P=0.018) and between the PSV and growth discordance (P=0.032). In monochorionic twin, linear correlation was shown between the AoI PI and birthweight (P=0.004) and between AoI PI and growth discordance (P=0.031). Also, the meaningful correlation between the PSV and birthweight (P=0.036) was found by using logistic regression analyses.

Conclusion

On the basis of our observation, AoI PI has revealed their hemodynamic status and this result may improve the understanding of growth patterns in twins.

Foetal aortic flow velocity waveforms in healthy and hypertensive pregnant women

Background

The foetal aortic Doppler frequency spectrum is influenced by cardiac output and contractility of the foetal heart as well as vascular compliance, blood viscosity and impedance of the arterial vascular system. The present study aimed at comparing Doppler flow pulsatility (PI) and resistance (RI) indexes of foetal proximal descending aorta (AoF) in the first, second and third trimesters of pregnancy, in low risk women and in those with chronic arterial hypertension, who had normal pregnancy outcomes.

Methods

A longitudinal and prospective study was carried out in 101 singleton pregnancies (71 low-risk pregnancies and 30 with essential hypertension). Multivariate regression had to be considered due to the experiment’s nature: two different indexes were read on the same set of individuals, once at each trimester of the pregnancy [1^st (11–14 weeks), 2^nd (19–22 weeks) and 3^rd (28–32 weeks) trimesters]. The response variable was denoted as index d, in a subject with hypertensive status h (hypertensive or normotensive), at continuous time t.

Results

In both groups, AoF-PI and AoF-RI showed a small, but significant increase from the first to the second (1.850 ± 0.339 vs 2.110 ± 0.242 for PI, and 0.829 ± 0.068 vs 0.857 ± 0.038 for RI; p < 0.001) and the first to the third (1.850 ± 0.339 vs 2.163 ± 0.282 for PI, and 0.829 ± 0.068 vs 0.864 ± 0.037 for RI; p < 0.001) trimesters of pregnancy. The global model showed that while AoF-RI trends were converging as time progressed, the AoF-PI values exhibited a divergent trend (p < 0.05).

Conclusions

Chronic stable hypertension in pregnancies with normal outcome, evidences an upward regular trend of foetal descending aorta pulsatility index that is similar to the normotensive condition.

Reference values for fetal aortic isthmus blood flow parameters at 24 to 38 weeks' gestation

OBJECTIVE

The goal of this study is to establish population-specific nomograms of fetal aortic isthmus (AoI) Doppler indices in the period of 24-38 weeks' gestation.

METHODS

This was a cross-sectional study of 240 Asian singleton pregnant women at 24-38 completed weeks' gestation. Fetal AoI blood flow was evaluated by Doppler study with automatic calculation of pulsatility index, resistance index, peak systolic velocity, end-diastolic velocity, and time-averaged maximum velocity. The relationship of these indices and gestational age was estimated by using regression analysis, and the best predictive models were determined to define mean, 5th, and 95th centile of each gestational age. The reproducibility was expressed by intraclass correlation coefficients and limits of agreement.

RESULTS

The mean maternal age was 28 ± 5.7 years. A total of 97% of all attempts to obtain AoI Doppler waveforms were successful with high interobserver and intraobserver reproducibility. Pulsatility index and peak systolic velocity significantly correlated with gestational age (P = 0.03 and 0.001, respectively), whereas no significant change of resistance index, end-diastolic velocity, and time-averaged maximum velocity with advancing gestation was observed.

CONCLUSION

This study offers normative values of fetal AoI Doppler indices, which may be useful in the difficult task of fetal surveillance in growth-restricted fetuses among our population.

The fetal cardiovascular response to increased placental vascular impedance to flow determined with 4-dimensional ultrasound using spatiotemporal image correlation and virtual organ computer-aided analysis

OBJECTIVE

We sought to determine if increased placental vascular impedance to flow is associated with changes in fetal cardiac function using spatiotemporal image correlation and virtual organ computer-aided analysis.

STUDY DESIGN

A cross-sectional study was performed in fetuses with umbilical artery pulsatility index >95th percentile (abnormal [ABN]). Ventricular volume (end-systole, end-diastole), stroke volume, cardiac output (CO), adjusted CO, and ejection fraction were compared to those of 184 normal fetuses.

RESULTS

A total of 34 fetuses were evaluated at a median gestational age of 28.3 (range, 20.6-36.9) weeks. Mean ventricular volumes were lower for ABN than normal cases (end-systole, end-diastole) with a proportionally greater decrease for left ventricular volume (vs right). Mean left and right stroke volume, CO, and adjusted CO were lower for ABN (vs normal) cases. Right ventricular volume, stroke volume, CO, and adjusted CO exceeded the left in ABN fetuses. Mean ejection fraction was greater for ABN than normal cases. Median left ejection fraction was greater (vs right) in ABN fetuses.

CONCLUSION

Increased placental vascular impedance to flow is associated with changes in fetal cardiac function.

Fetal left modified myocardial performance index: technical refinements in obtaining pulsed-Doppler waveforms

OBJECTIVE

To assess the influence of machine settings (wall motion filter (WMF), angle of insonation, Doppler aliasing) and phase of valve clicks on repeatability of measurement of the fetal left modified myocardial performance index (Mod-MPI).

METHODS

Fetal left Mod-MPI was evaluated prospectively in 157 morphologically normal fetuses at 19-36 weeks' gestation. In a baseline cohort, a previously published technique and settings were used for measurement of Mod-MPI. In a second cohort, the influence of WMF, angle of insonation, Doppler aliasing and selection of the phase of the valve clicks on repeatability of measurement of Mod-MPI was assessed.

RESULTS

The intraclass correlation coefficient (ICC) for measurement repeatability in the baseline cohort was 0.22. Increase in WMF to 300 Hz or 500 Hz was associated with an increase in ICC to 0.60 and 0.55, respectively. An angle of insonation of < 15° was associated with an increase in ICC to 0.79 and 0.78 at a WMF of 300 and 500 Hz, respectively. A WMF of 300 Hz, angle of insonation of < 15° and absence of aliasing was associated with an increase in ICC to 0.85 and 0.87 at the beginning and peak of the valve click, respectively. Mod-MPI ranged from 0.35 to 0.48. An increase in calculated MPI was associated with increasing WMF, selection of the beginning vs. peak of the valve clicks and increase in angle of insonation. The presence or absence of aliasing had no effect.

CONCLUSIONS

Refinement of machine settings improves repeatability of Mod-MPI, as does selection of the peak of the valve click. We suggest a consensus be reached as to the precise measurement of MPI, but for the moment would suggest: WMF, 300 Hz; angle of insonation, < 15°; avoiding Doppler aliasing; and selection of valve click peak. Systematic variation in measurement of time intervals may be responsible for the widely varying published normal ranges for Mod-MPI.

Longitudinal study of aortic isthmus Doppler in appropriately grown and small-for-gestational-age fetuses with normal and abnormal umbilical artery Doppler

OBJECTIVE

To establish reference ranges using longitudinal data for aortic isthmus (AoI) Doppler indices in appropriate-for-gestational-age (AGA) fetuses and to document the longitudinal trends in a cohort of small-for-gestational-age (SGA) fetuses with normal umbilical artery Doppler and in fetuses with intrauterine growth restriction (IUGR) and abnormal umbilical artery Doppler.

METHODS

AoI Doppler reference ranges were established from longitudinal data on 72 AGA singleton fetuses. Reliability of AoI Doppler flow measurements at two different sites and reproducibility between two operators was reviewed. A prospective longitudinal study of AoI Doppler indices in 48 SGA fetuses with normal umbilical artery Doppler and 10 IUGR fetuses was performed.

RESULTS

The AoI pulsatility index (PI) and peak systolic velocity (PSV) in AGA fetuses showed a significant increase with gestational age. Analysis of intra- and interoperator variability revealed no significant mean difference in measurements of AoI-PI or AoI-PSV. Observations of AoI-PI and AoI-PSV from SGA fetuses did not differ significantly from those of AGA or IUGR fetuses. Retrograde flow in the AoI did not predate changes in the ductus venosus in IUGR fetuses.

CONCLUSIONS

Reference ranges for fetal AoI Doppler parameters in AGA fetuses constructed using longitudinal data are consistent with those obtained from cross-sectional data. The AoI Doppler parameters in SGA fetuses did not differ from those in AGA fetuses. Preterm IUGR fetuses did not manifest alterations in AoI-PI or AoI-PSV prior to changes in biophysical profile or ductus venosus Doppler. Further large-scale prospective studies are needed to determine whether AoI Doppler parameters are of any value in timing delivery or reducing adverse neurodevelopmental outcome.

Assessment of uterine artery and aortic isthmus Doppler recordings as predictors of necrotizing enterocolitis

OBJECTIVE

The purpose of this study was to evaluate whether changes of uterine arteries and aortic isthmus Doppler blood flow recordings could enhance the prediction of necrotizing enterocolitis.

STUDY DESIGN

Doppler characteristics of the uterine artery, umbilical and middle cerebral arteries, ductus venosus, and aortic isthmus were reviewed in 123 growth-restricted fetuses who were then divided into 2 groups: with and without necrotizing enterocolitis.

RESULTS

Twelve of 123 newborn infants (9%) expressed necrotizing enterocolitis. This group showed significant association between necrotizing enterocolitis and bilateral notching on the uterine artery (83.3% vs 29.7%; P < .001), uterine artery mean resistance index (83.3% vs 36.9%; P < .002), aortic isthmus diastolic blood flow velocity integrals (Z score: -7.32 vs -3.99; P = .028), and absent or negative "a" wave on the ductus venosus (17% vs 1.8%; P = .021). With the use of logistic regression, uterine bilateral notching could predict necrotizing enterocolitis with a sensitivity of 83.3% and a specificity of 70.3%.

CONCLUSION

More than any other variable, uterine bilateral notching should be recognized as a strong risk factor for necrotizing enterocolitis.

Restriction of placental vasculature in a non-human primate: a unique model to study placental plasticity

The limits of placental plasticity, i.e., the ability of the placenta to adapt and alter its growth trajectory in response to altered fetal requirements, are not known. We report fetal and placental hemodynamic adaptations in a novel non-human primate model in which the fetal inter-placental bridging vessels were surgically ligated. Doppler ultrasound studies showed that the rhesus placenta compensates for an approximate 40% reduction in functional capacity by increased growth and maintenance of umbilical volume blood flow. This unique experimental animal model has applications for mechanistic studies of placental plasticity and the impact on fetal development.

Changes in myocardial performance index and aortic isthmus and ductus venosus Doppler in term, small-for-gestational age fetuses with normal umbilical artery pulsatility index

OBJECTIVE

To evaluate the changes in myocardial performance index (MPI) and aortic isthmus (AoI) and ductus venosus (DV) Doppler in term, small-for-gestational age (SGA) fetuses with normal umbilical artery (UA) Doppler.

METHODS

MPI, AoI and DV pulsatility indices (PI) were measured within 1 week prior to delivery in a cohort of 178 term singleton consecutive SGA fetuses with normal UA-PI (< 95(th) percentile) and 178 controls matched by gestational age. Cardiovascular parameters were converted into Z-scores and values above the 95(th) centile defined as abnormal.

RESULTS

Median gestational age at inclusion and at delivery was 35.7 and 38.6 weeks, respectively. Compared to controls, SGA fetuses showed significantly higher values in MPI and AoI-PI and similar values in DV-PI. SGA fetuses showed a significantly higher proportion of increased MPI (28.1 vs. 6.7%; P < 0.01) and abnormal AoI-PI (14.6 vs. 5.1%; P < 0.01) than controls. The proportion of cases with abnormal DV-PI was similar between SGA cases and controls. Retrograde net blood flow in the AoI was observed in 7.3% of the SGA cases and in none of the controls.

CONCLUSION

A proportion of SGA fetuses show cardiovascular Doppler abnormalities. This information might be of clinical relevance in improving the detection and management of late-onset intrauterine growth restriction.

Aortic isthmus and cardiac monitoring of the growth-restricted fetus

Aortic isthmus acts as an arterial watershed between the cerebral and placental circulations, connecting 2 parallel fetal ventricular pumps. It plays a crucial role in the fetal circulatory dynamics. Information about aortic isthmus blood flow may improve the management of sick fetuses. However, perceived technical difficulties limit the clinical use of aortic isthmus Doppler for fetal hemodynamic monitoring. Changes in aortic isthmus blood flow pattern seem to reflect fetal cardiovascular status accurately and predict perinatal and long-term neurodevelopmental outcome in intrauterine growth restriction. This review evaluates the available scientific information and discusses the role of aortic isthmus in fetal circulation.

Impact of congenital heart disease on brain development and neurodevelopmental outcome

Advances in cardiac surgical techniques and perioperative intensive care have led to improved survival in babies with congenital heart disease (CHD). While it is true that the majority of children with CHD today will survive, many will have impaired neurodevelopmental outcome across a wide spectrum of domains. While continuing to improve short-term morbidity and mortality is an important goal, recent and ongoing research has focused on defining the impact of CHD on brain development, minimizing postnatal brain injury, and improving long-term outcomes. This paper will review the impact that CHD has on the developing brain of the fetus and infant. Neurologic abnormalities detectable prior to surgery will be described. Potential etiologies of these findings will be discussed, including altered fetal intrauterine growth, cerebral blood flow and brain development, associated congenital brain abnormalities, and risk for postnatal brain injury. Finally, reported neurodevelopmental outcomes after surgical repair of CHD will be reviewed.

Usefulness of myocardial tissue Doppler vs conventional echocardiography in the evaluation of cardiac dysfunction in early-onset intrauterine growth restriction

OBJECTIVE

To evaluate cardiac function by tissue Doppler imaging vs conventional echocardiography in intrauterine growth restriction.

STUDY DESIGN

A prospective study in 25 intrauterine growth restriction, and in 50 normally grown fetuses between 24 and 34 weeks. Conventional echocardiography (E/A ratios, outflow tract velocities and myocardial performance index), and tissue Doppler (myocardial peak velocities, E'/A' ratios and myocardial performance index') measurements were performed.

RESULTS

With conventional echocardiography, intrauterine growth restriction fetuses showed an increase in left myocardial performance index but similar values of E/A ratios, outflow tract velocities and right myocardial performance index as compared with controls. Tissue Doppler imaging demonstrated that intrauterine growth restriction fetuses had significantly lower systolic and diastolic myocardial velocities in mitral and tricuspid annulus, higher mitral E'/A' ratio and higher mitral, tricuspid and septal myocardial performance index' values.

CONCLUSION

Tissue Doppler imaging demonstrated the presence of both systolic and diastolic cardiac dysfunction in intrauterine growth restriction. Tissue Doppler imaging may constitute a more sensitive tool than conventional echocardiography to evaluate cardiac dysfunction in intrauterine growth restriction.

Repeatability and reproducibility of fetal cardiac ventricular volume calculations using spatiotemporal image correlation and virtual organ computer-aided analysis

OBJECTIVE

The objective of this study was to quantify the repeatability and reproducibility of fetal cardiac ventricular volumes obtained using spatiotemporal image correlation (STIC) and Virtual Organ Computer-Aided Analysis (VOCAL; GE Healthcare, Kretztechnik, Zipf, Austria).

METHODS

A technique was developed to compute ventricular volumes using the subfeature Contour Finder: Trace. Twenty-five normal pregnancies were evaluated for the following: (1) to compare the coefficient of variation (CV) of ventricular volumes obtained using 15 degrees and 30 degrees rotation; (2) to compare the CV between 3 methods of quantifying ventricular volumes: (a) Manual Trace, (b) Inversion Mode, and (c) Contour Finder: Trace; and (3) to determine repeatability by calculating agreement and reliability of ventricular volumes when each STIC was measured twice by 3 observers. Reproducibility was assessed by obtaining 2 STICs from each of 44 normal pregnancies. For each STIC, 2 ventricular volume calculations were performed, and agreement and reliability were evaluated. Additionally, measurement error was examined.

RESULTS

(1) Agreement was better with 15 degrees rotation than 30 degrees (15 degrees: 3.6%; 95% confidence interval [CI], 3.0%-4.2%; versus 30 degrees: 7.1%; 95% CI, 5.8%-8.6%; P < .001); (2) ventricular volumes obtained with Contour Finder: Trace had better agreement than those obtained using either Inversion Mode (Contour Finder: Trace: 3.6%; 95% CI, 3.0%-4.2%; versus Inversion Mode: 6.0%; 95% CI, 4.9%-7.2%; P < .001) or Manual Trace (10.5%; 95% CI, 8.7%-12.5%; P < .001); (3) ventricular volumes were repeatable with good agreement and excellent reliability for both intraobserver and interobserver measurements; and (4) ventricular volumes were reproducible with negligible differences in agreement and good reliability. In addition, bias between STIC acquisitions was minimal (<1%; mean percent difference, -0.4%; 95% limits of agreement, -5.4%-5.9%).

CONCLUSIONS

Fetal echocardiography using STIC and VOCAL allows repeatable and reproducible calculation of ventricular volumes with the subfeature Contour Finder: Trace.

Contribution of the myocardial performance index and aortic isthmus blood flow index to predicting mortality in preterm growth-restricted fetuses

OBJECTIVES

To evaluate the predictive value for perinatal death of the myocardial performance index (MPI) and aortic isthmus flow index (IFI), as isolated parameters and in a combined model including currently used Doppler indices, in preterm growth restricted (IUGR) fetuses.

METHODS

Umbilical artery, fetal middle cerebral artery (MCA) and ductus venosus (DV) pulsatility indices (PIs) were recorded, along with IFI and MPI, in a cohort of 97 preterm (delivered at between 24 and 34 weeks) IUGR fetuses. Logistic regression analysis was performed to identify those variables that were independently associated with perinatal mortality, and an algorithm to estimate probability of death was constructed including the best combination of parameters.

RESULTS

With the exception of MCA, all Doppler indices were significantly associated with perinatal death as isolated parameters, but only DV-PI and MPI were found to be independent predictors on multivariate analysis. An algorithm combining DV atrial flow (positive or absent/reversed) and MPI (normal or above 95(th) percentile) had a better predictive accuracy than did any single parameter. The risk for death in IUGR fetuses below 28 weeks' gestation with present atrial flow in the DV and normal MPI was 18%, with either characteristic abnormal it was 70-73%, and with both abnormal it was 97%. The risk for death in IUGR fetuses above 28 weeks with present atrial flow in the DV and normal MPI was 0.1%, with either abnormal it was 6-7%, and with both abnormal it was 45%.

CONCLUSIONS

MPI is an independent predictor of perinatal death in preterm IUGR fetuses with accuracy similar to that of DV flow. A combination of DV flow with MPI may better stratify the estimated probability of death. IFI does not add to the prediction of perinatal death when used in combination with DV flow.

The role of Doppler and placental screening

Placental-associated diseases account for most cases of adverse perinatal outcome in developing countries. Uterine Doppler evaluation predicts most instances of early-onset preeclampsia and intrauterine growth restriction, but there is no evidence in favour of any prophylactic strategy in cases of an abnormal screening result. Umbilical artery Doppler investigation allows identifying those small-for-gestational-age foetuses at higher risk, and its use in these pregnancies improves a number of perinatal outcomes. Middle cerebral artery Doppler investigation reflects brain redistribution, and its use in combination with the umbilical artery in a cerebroplacental ratio seems to improve prediction of adverse outcome, mainly in near-term pregnancies, where most instances of adverse outcome occur in foetuses with normal umbilical artery. Ductus venosus Doppler waveform is a surrogate parameter of the foetal acid-base status. However, the benefits of its use in the management of early-onset growth restriction needs further evidence.

Fetal aortic isthmus blood flow and the fraction of cardiac output distributed to the upper body and brain at 11-20 weeks of gestation

OBJECTIVE

To measure serial changes in fetal aortic isthmus (AI) blood flow and estimate the fraction of fetal cardiac output distributed to the upper body, including the brain, at 11-20 weeks of gestation.

METHODS

Using pulsed-wave Doppler and two-dimensional ultrasound, blood flow velocities and inner diameter of the AI, aortic valve (AV) and pulmonary valve (PV) were measured longitudinally in 143 fetuses and volume blood flows (Q) were calculated for each site using the formula: Q (mL/min) = pix (diameter/2)(2) x velocity time integral x heart rate x 60. The sum of Q(av) and Q(pv) constituted the combined cardiac output (CCO) and the fraction (%) of the upper body (including brain) blood flow was calculated as: (Q(av)-Q(ai))x100/CCO.

RESULTS

AI blood velocities as well as the vessel diameter increased with advancing gestation, resulting in a significant increase in Q(ai) from 1.9 to 40.5 mL/min during weeks 11 to 20. The AI peak systolic velocity increased from 29 to 63 cm/s, end-diastolic velocity from 1.2 to 5.2 cm/s, and the time-averaged maximum velocity from 11 to 22 cm/s, resulting in a fairly stable pulsatility index (PI) of 2.4-2.6 and resistance index (RI) of 0.91-0.94. On average, 75% of blood ejected by the left ventricle (which represented about 35% of the CCO) passed through the AI to the descending aorta. The fraction of CCO distributed to the upper body, including the brain, was estimated as approximately 13%.

CONCLUSION

We have established longitudinal reference ranges for fetal AI diameter, blood flow velocities, PI, RI and volume blood flow at 11-20 weeks of gestation. The human fetus appears to direct a relatively small fraction (13%) of its CCO to the upper body, including the brain, during this period of pregnancy.

Monitoring of fetuses with intrauterine growth restriction: longitudinal changes in ductus venosus and aortic isthmus flow

OBJECTIVES

To explore in growth-restricted fetuses the sequence of changes in aortic isthmus and ductus venosus blood flow in relation to other arterial Doppler parameters commonly used to evaluate fetal wellbeing.

METHODS

Umbilical and middle cerebral arteries, ductus venosus and aortic isthmus were explored serially by means of pulsed Doppler in a cohort of singleton small-for-gestational age fetuses requiring delivery before 34 weeks. Longitudinal changes in the last 30 days before delivery were modeled by multilevel analysis. Individual regression lines for each variable were calculated for each fetus and from these the regression lines for the whole group were derived, in order to estimate the mean time point at which each Doppler parameter became abnormal (outside the 5th-95th centile range). A survival analysis was performed during the monitoring period, in which the endpoint was an abnormal Doppler pulsatility index.

RESULTS

A total of 162 observations were performed on 46 fetuses (median, 3; range, 2-10). The median gestational age at inclusion was 28.9 (range, 23.6-33.4) weeks and delivery occurred at a median gestational age of 30.5 (range, 25.9-33.9) weeks. Six (13%) cases of perinatal mortality occurred. Umbilical and middle cerebral artery Doppler showed an almost linear deterioration throughout monitoring, becoming abnormal on average 24 days and 20 days before delivery, respectively. Aortic isthmus Doppler became abnormal on average 13 days before delivery, while ductus venosus Doppler did so within the last week before delivery.

CONCLUSIONS

In preterm growth-restricted fetuses, aortic isthmus blood flow becomes abnormal on average 1 week earlier than does that in the ductus venosus. This could provide a sound basis to better define management protocols aimed to improve intact fetal survival.

Relationship between aortic isthmus and ductus venosus velocity waveforms in severe growth restricted fetuses

OBJECTIVE

To evaluate the incidence of abnormalities in velocity waveforms from ductus venosus (DV) and aortic isthmus (AoI) in fetuses with intrauterine growth restriction (IUGR) and their reciprocal temporal relationship.

METHODS

DV and AoI velocity waveforms were recorded in 31 IUGR fetuses characterized either by absent end diastolic (20) or reverse flow (11) in umbilical artery. Abnormal velocity waveforms in DV and AoI were defined in presence of reverse diastolic flows.

RESULTS

Abnormal DV velocity waveforms were present in 10 fetuses and were always associated with abnormalities. Abnormal AoI flows were also present in 10 fetuses of the remaining 21 fetuses with normal DV velocity waveforms (47.6%). Longitudinal monitoring of fetuses with normal DV flows showed a significantly shorter time interval in the onset of reverse flow in DV when abnormalities in AoI were present (4 vs 14 days p=0.001) irrespectively of gestational age or other potential confounding variables.

CONCLUSIONS

Our data suggest that AoI velocity waveforms become abnormal at an earlier stage of fetal compromise than DV.

Use of the 3-vessel view to record Doppler velocity waveforms from the aortic isthmus in normally grown and growth-restricted fetuses: comparison with the long aortic arch view

OBJECTIVE

Aortic isthmus (AoI) velocity waveforms are considered powerful indicators of hemodynamic deterioration in intrauterine growth-restricted (IUGR) fetuses. However, technical difficulties in sampling AoI velocity waveforms from the longitudinal aortic arch (LAA) have limited its clinical application thus far. In this study, we tested the possibility of recording AoI velocity waveforms from the 3-vessel (3V) view of the fetal mediastinum and comparing the agreement of these measurements with recordings from the LAA.

METHODS

Doppler measurements of the pulsatility index (PI) from the AoI were performed in 70 fetuses (20 IUGR and 50 normally grown) between 20 and 34 weeks' gestation. All measurements were sampled in both the LAA and 3V views by the same investigator. Reliability was evaluated with intraclass correlation coefficients (ICCs), and Bland-Altman plots were generated. The time required to complete the measurements was compared.

RESULTS

A high degree of reliability was observed between PI values obtained from LAA and 3V views in both IUGR and normally grown fetuses (all fetuses: ICC, 0.976; 95% confidence interval [CI], 0.961-0.985; normally grown: ICC, 0.839; 95% CI, 0.731-0.906; IUGR: ICC, 0.954; 95% CI, 0.886-0.982). However, recordings from the 3V view were significantly less time-consuming than those from the LLA view (mean +/- SD, 30.4 +/- 14.2 versus 52.8 +/- 29.4 seconds; P < .0001) and showed higher intraobserver reproducibility.

CONCLUSIONS

In IUGR and normally grown fetuses, AoI waveforms can be reliably obtained from the 3V view with higher reproducibility and a shorter recording time.

Doppler assessment of the aortic isthmus and perinatal outcome in preterm fetuses with severe intrauterine growth restriction

OBJECTIVES

To evaluate the characteristics and association with perinatal outcome of the aortic isthmus (AoI) circulation as assessed by Doppler imaging in preterm growth-restricted fetuses with placental insufficiency.

METHODS

This was a prospective cross-sectional study. Fifty-one fetuses with intrauterine growth restriction (IUGR) and either an umbilical artery (UA) pulsatility index (PI) > 95(th) centile or a cerebroplacental ratio < 5(th) centile were examined at 24-36 weeks' gestation. AoI impedance indices (PI and resistance index) and absolute velocities (peak systolic (PSV), end-diastolic and time-averaged maximum (TAMXV) velocities), were measured in all cases and compared with reference ranges by gestational age. Furthermore, fetuses were stratified into two groups according to the direction of the diastolic blood flow in the AoI: those with antegrade flow (n = 41) and those with retrograde flow (n = 10). Clinical surveillance was based on gestational age and Doppler assessment of the UA, middle cerebral artery and ductus venosus (DV). Adverse perinatal outcome was defined as stillbirth, neonatal death and severe morbidity (respiratory distress syndrome, bronchopulmonary dysplasia, Grade III/IV intraventricular hemorrhage, necrotizing enterocolitis and a neonatal intensive care unit stay > 14 days).

RESULTS

Adverse perinatal outcome was significantly associated with an increased AoI-PI (area under the curve 0.77; 95% CI, 0.63-0.92; P < 0.005). A significant correlation (P < 0.001) was found between retrograde blood flow in the AoI and adverse perinatal outcome, the overall perinatal mortality being higher in the retrograde group (70% vs. 4.8%, P < 0.001). In 4/5 (80%) fetuses the reversal of flow in the AoI preceded that in the DV by 24-48 h. AoI-PSV and AoI-TAMXV were < 5(th) centile in 40/51 (78%) and 48/51 (94%) cases, respectively, whereas AoI-PI was > 95(th) centile in 21/51 (41%) cases.

CONCLUSIONS

Retrograde flow in the AoI in growth-restricted fetuses correlates strongly with adverse perinatal outcome. Absolute velocities in the AoI are decreased in growth-restricted fetuses. The data suggest a potential role for Doppler imaging of the AoI in the clinical surveillance of fetuses with severe IUGR, which should be confirmed in larger prospective studies.

Fetal cardiac output, distribution to the placenta and impact of placental compromise

OBJECTIVES

Intrauterine growth restriction is a common clinical problem, but the underlying hemodynamic changes are not well known. Our aim was to determine the normal distribution of fetal cardiac output to the placenta during the second half of pregnancy, and to assess the changes imposed by growth restriction with various degrees of placental compromise.

METHODS

A cross-sectional study of 212 low-risk pregnancies with a gestational age of 18-41 weeks constituted the reference population. A second group of 64 pregnancies with an estimated fetal weight <or = 2.5(th) percentile constituted the study group. Ultrasound measurements of inner diameters and velocities at the fetal left and right ventricular outlets and intra-abdominal umbilical vein were used to determine combined left and right cardiac output (CCO) and the fraction distributed to the placenta. Placental compromise was graded according to umbilical artery waveform: pulsatility index normal, > 97.5th percentile, or absent/reversed end-diastolic velocity. Regression analysis and Z-score (SD-score) statistics were used to establish normal ranges and to compare groups.

RESULTS

During gestational weeks 18-41 the normal CCO/kg was on average 400 mL/min/kg and the fraction directed to the placenta was on average 32%, while after 32 weeks it was 21%. In intrauterine growth restriction the CCO/kg was not significantly different, but the fraction to the placenta was lower (P < 0.001). This effect was more pronounced in severe placental compromise (P < 0.001).

CONCLUSIONS

Normally, one third of the fetal CCO is distributed to the placenta in most of the second half of pregnancy, and one fifth near term. In placental compromise this fraction is reduced while CCO/kg is maintained at normal levels, signifying an increased recirculation of umbilical blood in the fetal body.

Reference ranges for Doppler parameters of the fetal aortic isthmus during the second half of pregnancy

OBJECTIVE

To establish reference ranges for blood flow velocity waveforms (FVW) of the fetal aortic isthmus (AoI) during the second and third trimesters of pregnancy.

METHODS

This was a prospective cross-sectional observational study involving 458 uncomplicated singleton pregnancies between 19 and 37 weeks of gestation. Fetal AoI Doppler parameters were assessed in either the longitudinal aortic arch view or the three vessels and trachea view. Regression analysis was used to determine gestational-age-specific reference ranges and to construct nomograms for the following Doppler parameters: pulsatility index (PI), resistance index (RI) and peak systolic (PSV), end-diastolic (EDV) and time-averaged maximum (TAMXV) velocities. Intra- and interobserver reproducibility were evaluated by calculating intraclass correlation coefficients (ICCs) and limits of agreement.

RESULTS

Reliable FVW in the AoI were obtained in all cases. Acceptable intra- and interobserver reproducibility was obtained. With advancing gestation, there was a significant increase in PSV, TAMXV and PI, whereas RI and EDV remained constant during the second half of pregnancy. No cases of absent or reversed flow during diastole were detected.

CONCLUSION

Normal data of the fetal AoI blood FVW throughout the second and third trimesters of pregnancy are provided. The reported Doppler profiles may be of clinical use in the assessment of hemodynamically compromised growth-restricted fetuses.