The normal diameter of the fetal aorta and pulmonary artery: echocardiographic evaluation in utero

Area of the Fetal Ascending and Descending Aorta by Spatiotemporal Image Correlation in the Rendering Mode: Reproducibility and Comparison with Pregestational Diabetic Mothers

Background

The objective of this study was to assess the ascending and descending aorta area measurements by three-dimensional (3D) ultrasound using spatiotemporal image correlation (STIC) in the rendering mode comparing these measurements with pregestational diabetic mothers and assessing the reproducibility of the method.

Methods

We carried out a retrospective cross-sectional study with 58 normal and nine fetuses from pregestational diabetic mothers between 20 and 33 + 6 weeks of gestation. Fetal heart volumes were acquired at the level of four-chamber view to obtain the reconstructed planes for the ascending and descending aorta areas in the rendering mode. Linear regression was performed to assess the correlation between the fetal aorta areas and gestational age (GA). To assess the intra- and interobserver reproducibility, we used the concordance correlation coefficient (CCC).

Results

The mean ascending and descending aorta areas were 0.12 (0.02-0.48) and 0.11 (0.04-0.39) cm2 in normal fetuses, respectively. There was a moderate positive correlation between GA and ascending aorta area measurements (0.005676*GA - 0.01283; r = 0.53, P < 0.0001) and strong positive correlation between GA and descending aorta area (0.01095*GA - 0.1581; r = 0.68, P < 0.0001). We observed a weak intra- and interobserver reproducibility with CCC ranging from 0.05 to 0.91. The mean difference in the ascending and descending aorta area measurements of normal and fetuses of pregestational diabetic mothers was -0.03 cm2 (P = 0.276) and -0.03 cm2 (P = 0.231), respectively.

Conclusion

The fetal ascending and descending aorta area measurements obtained by 3D ultrasound using STIC in the rendering mode increased with GA in normal fetuses. The method showed weak intra- and interobserver reproducibility.

Unfavorable postnatal outcome with significant dilation of the fetal main pulmonary artery near term

INTRODUCTION

Fetal echocardiography in third trimester is relatively rare reported and there is no data, what is the clinical meaning of the main pulmonary artery (MPA) dilatation in third trimester or before the delivery in fetuses with congenital heart defect. We analyzed the neonatal follow-up in cases of significantly dilated MPA diameter to better understand its clinical significance.

MATERIAL AND METHODS

Retrospectively 238 healthy singleton fetuses were selected as a reference group. Consecutive percentiles for MPA diameter according to the gestational age were calculated. In second step, we selected cases whose MPA diameter measured at the level of three vessel trachea view (3VT view) was pointedly above 95th centile in third trimester of pregnancy, according to the obtained data of our healthy population.

RESULTS

There were 11 fetuses, with dilated MPA diameter (range 12-13.5 mm), who had last echocardiography performed at 37.6 weeks of gestation. There were 11 isolated heart defects: 7 cases with HLHS, 2 with d-TGA, and 2 cases with CoA. Mean neonatal weight was 3,345 g, with Apgar score 8-10. About 10 newborns out of 11 had cardiac surgery at the mean 12th day of the postnatal life and 8 of them died on the mean 23rd day. Autopsy was performed in 5 cases. In all of them histopathology reports described pulmonary hypertension in addition to cardiac structural abnormalities.

CONCLUSION

Severe dilation of the fetal MPA before the delivery suggested prenatal abnormal lung development and was a poor prognostic factor. In these cases postnatal pulmonary hypertension should be suspected.

A Case Report of in Utero Williams Syndrome Arterial Malformation

INTRODUCTION

Williams syndrome (WS), an autosomal dominant condition linked to gene deletions on chromosome 7, can cause supravalvular aortic narrowing and death. WS-associated mutations are believed to disrupt arterial elastin fibers, causing smooth muscle malformation, endomysial fibrosis and severe hypertension. Previous studies demonstrated arterial ultrastructural anomalies in adult WS patients. It is not presently known if the arterial phenotype of WS is also present in utero.

CASE REPORT

A 34-week stillborn was delivered to a 28-year-old with genetically confirmed WS. Aortic tissue from the patient was compared with non-WS fetal aorta of similar gestational age using EM and light microscopy. Both sections were taken from the proximal aortic root. This demonstrated internal elastic lamina disruption, malformed elastic fibers, smooth muscle proliferation and abnormal collagen fibers, consistent with adult WS phenotype.

CONCLUSION

Our analysis indicated the cardiovascular changes of WS in a fetus as young as 34 weeks.

Magnetic resonance angiography of fetal vasculature at 3.0 T

Magnetic resonance angiography has not been used much previously for visualizing fetal vessels in utero for reasons that include a contraindication for the use of exogenous contrast agents, maternal respiratory motion and fetal motion. In this work, we report the feasibility of using an appropriately modified clinical time-of-flight magnetic resonance imaging sequence for non-contrast angiography of human fetal and placental vessels at 3.0 T. Using this 2D angiography technique, it is possible to visualize fetal vascular networks in late pregnancy.

KEY POINTS

• 3D-visualization of fetal vasculature is feasible using non-contrast MRA at 3.0 T. • Visualization of placental vasculature is also possible with this method. • Fetal MRA can serve as a vascular localizer for quantitative MRI studies. • This method can be extended to 1.5 T.

Adjustable fetal phantom for pulse oximetry

As the measuring head of a fetal pulse oximeter must be attached to the head of the fetus inside the mother's uterus during labor, testing, and developing of fetal pulse oximeters in real environment have several difficulties. A fetal phantom could enable evaluation of pulse oximeters in a simulated environment without the restrictions and difficultness of medical experiments in the labor room. Based on anatomic data we developed an adjustable fetal head phantom with three different tissue layers and artificial arteries. The phantom consisted of two arteries with an inner diameter of 0.2 and 0.4 mm. An electronically controlled pump produced pulse waves in the arteries. With the phantom we investigated the sensitivity of a custom-designed wireless pulse oximeter at different pulsation intensity and artery diameters. The results showed that the oximeter was capable of identifying 4% and 2% changes in diameter between the diastolic and systolic point in arteries of over 0.2 and 0.4 mm inner diameter, respectively. As the structure of the phantom is based on reported anatomic values, the results predict that the investigated custom-designed wireless pulse oximeter has sufficient sensitivity to detect the pulse waves and to calculate the R rate on the fetal head.

Neonatal Aortic Arch Hemodynamics and Perfusion During Cardiopulmonary Bypass

The objective of this study is to quantify the detailed three-dimensional (3D) pulsatile hemodynamics, mechanical loading, and perfusion characteristics of a patient-specific neonatal aortic arch during cardiopulmonary bypass (CPB). The 3D cardiac magnetic resonance imaging (MRI) reconstruction of a pediatric patient with a normal aortic arch is modified based on clinical literature to represent the neonatal morphology and flow conditions. The anatomical dimensions are verified from several literature sources. The CPB is created virtually in the computer by clamping the ascending aorta and inserting the computer-aided design model of the 10 Fr tapered generic cannula. Pulsatile (130 bpm) 3D blood flow velocities and pressures are computed using the commercial computational fluid dynamics (CFD) software. Second order accurate CFD settings are validated against particle image velocimetry experiments in an earlier study with a complex cardiovascular unsteady benchmark. CFD results in this manuscript are further compared with the in vivo physiological CPB pressure waveforms and demonstrated excellent agreement. Cannula inlet flow waveforms are measured from in vivo PC-MRI and 3 kg piglet neonatal animal model physiological experiments, distributed equally between the head-neck vessels and the descending aorta. Neonatal 3D aortic hemodynamics is also compared with that of the pediatric and fetal aortic stages. Detailed 3D flow fields, blood damage, wall shear stress (WSS), pressure drop, perfusion, and hemodynamic parameters describing the pulsatile energetics are calculated for both the physiological neonatal aorta and for the CPB aorta assembly. The primary flow structure is the high-speed canulla jet flow (∼3.0 m/s at peak flow), which eventually stagnates at the anterior aortic arch wall and low velocity flow in the cross-clamp pouch. These structures contributed to the reduced flow pulsatility (85%), increased WSS (50%), power loss (28%), and blood damage (288%), compared with normal neonatal aortic physiology. These drastic hemodynamic differences and associated intense biophysical loading of the pathological CPB configuration necessitate urgent bioengineering improvements—in hardware design, perfusion flow waveform, and configuration. This study serves to document the baseline condition, while the methodology presented can be utilized in preliminary CPB cannula design and in optimization studies reducing animal experiments. Coupled to a lumped-parameter model the 3D hemodynamic characteristics will aid the surgical decision making process of the perfusion strategies in complex congenital heart surgeries.

Estudo morfométrico do coração fetal: sua utilização como parâmetro para análise ecocardiográfica

OBJETIVO: Avaliar o diâmetro, o perímetro e a área das valvas atrioventriculares do coração fetal, bem como a espessura das paredes ventriculares e os diâmetros das cavidades ventriculares. MATERIAIS E MÉTODOS: Foram dissecados 20 corações de fetos com idade gestacional entre 28 e 36 semanas. Em seguida foram medidos os diâmetros ântero-posterior e transverso e aferidos as áreas e os perímetros das valvas mitral e tricúspide, bem como foram medidas as espessuras das paredes ventriculares e os diâmetros de suas cavidades, utilizando-se um paquímetro com acurácia de1/10 mm. RESULTADOS: Os diâmetros ântero-posterior e transverso da valva atrioventricular esquerda mediram, em média, 10,35 ± 1,62 mm e 9,90 ± 1,79 mm, respectivamente, e os diâmetros ântero-posterior e transverso da valva atrioventricular direita, 10,98 ± 1,90 mm e 9,51 ± 1,81 mm, respectivamente. A área e o perímetro da valva mitral foram de 84,06 ± 25,09 mm² e 29,87 ± 3,96 mm, respectivamente. A área e o perímetro da valva tricúspide mediram, respectivamente, 84,49 ± 26,79 mm² e 28,44 ± 3,85 mm. No ventrículo direito a espessura da parede anterior foi de 5,00 ± 1,70 mm e a da parede posterior foi de 3,83 ± 0,91 mm; no ventrículo esquerdo a espessura da parede anterior foi de 4,25 ± 0,87 mm e a da parede posterior foi de 4,14 ± 0,89 mm. O septo interventricular teve espessura de 4,10 ± 1,13 mm. O ventrículo direito teve como diâmetro ântero-posterior 9,25 ± 0,85 mm, e como diâmetro transverso 8,24 ± 0,42 mm. O ventrículo esquerdo mediu 9,95 ± 0,37 mm para o diâmetro ântero-posterior e 9,20 ± 0,40 mm para o diâmetro transverso. CONCLUSÃO: O conhecimento dos dados morfométricos do coração do feto é de grande importância para o diagnóstico ecocardiográfico de possíveis malformações cardíacas.

Utility of cardiac monitoring in fetuses at risk for congenital heart block: the PR Interval and Dexamethasone Evaluation (PRIDE) prospective study

BACKGROUND

Anti-SSA/Ro-associated third-degree congenital heart block is irreversible, prompting a search for early markers and effective therapy.

METHODS AND RESULTS

One hundred twenty-seven pregnant women with anti-SSA/Ro antibodies were enrolled; 95 completed an evaluable course in 98 pregnancies. The protocol included fetal echocardiograms performed weekly from 16 to 26 weeks' gestation and biweekly from 26 to 34 weeks. PR intervals >150 ms were considered prolonged, consistent with first-degree block. Ninety-two fetuses had normal PR intervals. Neonatal lupus developed in 10 cases; 4 were neonatal lupus rash only. Three fetuses had third-degree block; none had a preceding abnormal PR interval, although in 2 fetuses >1 week elapsed between echocardiographic evaluations. Tricuspid regurgitation preceded third-degree block in 1 fetus, and an atrial echodensity preceded block in a second. Two fetuses had PR intervals >150 ms. Both were detected at or before 22 weeks, and each reversed within 1 week with 4 mg dexamethasone. The ECG of 1 additional newborn revealed a prolonged PR interval persistent at 3 years despite normal intervals throughout gestation. No first-degree block developed after a normal ECG at birth. Heart block occurred in 3 of 16 pregnancies (19%) in mothers with a previous child with congenital heart block and in 3 of 74 pregnancies (4%) in mothers without a previous child with congenital heart block or rash (P=0.067).

CONCLUSIONS

Prolongation of the PR interval was uncommon and did not precede more advanced block. There was a trend toward more congenital heart block in fetuses of women with previously affected offspring than those without previously affected offspring. Advanced block and cardiomyopathy can occur within 1 week of a normal echocardiogram without initial first-degree block. Echodensities and moderate/severe tricuspid regurgitation merit attention as early signs of injury.

Development of Z-scores for fetal cardiac dimensions from echocardiography

OBJECTIVES

Z-scores for cardiac dimensions are well established in postnatal life, but have yet to be developed for fetal cardiac dimensions. These would be of real advantage to the clinician in accurately quantifying size and growth of cardiac dimensions and to the researcher by allowing mathematical comparison of growth in differing subgroups of a disease. The purpose of this observational study, conducted at tertiary fetal medicine and cardiology units, was to produce formulae and nomograms allowing computation of Z-scores for fetal cardiac dimensions from knowledge of femur length (FL), biparietal diameter (BPD) or gestational age (GA) using fetal echocardiography.

METHODS

Seventeen fetal cardiac dimensions were measured in 130 pregnant women with singleton fetuses of gestational age 15-39 weeks. Regression equations were derived relating all dimensions to FL, BPD and GA. From the calculations, formulae were then developed allowing fetal cardiac Z-score computation.

RESULTS

The relationships between cardiac dimensions and FL, BPD or GA were described following natural log transformation. From this analysis, FL (taken as an expression of fetal size) had the highest correlation to fetal cardiac dimensions. From the developed nomograms, Z-scores of specific fetal cardiac structures could be estimated from knowledge of the FL, BPD or GA and echocardiographically derived measurements.

CONCLUSIONS

This study allowed computation of Z-scores in fetal life for 17 cardiac dimensions from FL, BPD or GA. Previous studies of normal data allowed qualitative assessment of where abnormal cardiac dimensions lay with regard to the normal range. Z-scores from this study allow quantitative analysis of where such dimensions lie relative to the mean. This permits exact assessment of growth of fetal cardiac structures in normal hearts and particularly in congenitally abnormal hearts where quantitative assessment of the growth of cardiac structures is important in analyzing and planning treatment strategies.

Three-dimensional and four-dimensional fetal echocardiography: a new frontier

PURPOSE OF REVIEW

One of the difficulties of conventional two-dimensional cardiac imaging is the inability to examine fetal cardiac anatomy from multiple angle planes. Three-dimensional and four-dimensional ultrasound allows the fetal examiner to more accurately accomplish this task. Currently, multiple disciplines may be involved in the examination of the fetal heart (pediatric cardiologists, obstetricians, maternal-fetal medicine specialists, and radiologists). The three-dimensional and four-dimensional imaging equipment used by these specialty physicians varies greatly. The purpose of this communication is to review techniques using three-dimensional and four-dimensional imaging that the pediatric cardiologist may not be exposed to in the clinical environment, however, in consulting with colleagues needs to have an understanding of these imaging modalities.

RECENT FINDINGS

The reconstruction of cardiac structures using this technology allows the examiner to view cardiac anatomy in a manner that was limited by previous two-dimensional imaging. Volume datasets are obtained in the three-dimensional static mode (no cardiac motion) or using four-dimensional - the three-dimensional heart is observed contracting during one or multiple cardiac cycles. Therefore, the fourth dimension is time. Using either three-dimensional or four-dimensional technology datasets are acquired, followed by image reconstruction. The image reconstruction enables the examiner to evaluate a two-dimensional image using multiple views, evaluate intracardiac anatomy at different depth planes, and recreate casts of blood flow of the chambers and great vessels.

SUMMARY

This new technology has enhanced the ability of the examiner to identify normal and complex fetal heart anatomy during the early second to the late third trimesters of pregnancy.

Prenatal sonographic features of isolated hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a spectrum of fetal conditions associated with severe hypoplasia of the left ventricle and left ventricular outflow tract. The purpose of this series was to focus on the sonographic prenatal features of isolated HLHS. Based on the 5 cases presented here, the prenatal sonographic features of HLHS include small-sized left ventricle, atretic or hypoplastic mitral valves with restricted motion and a small amount of antegrade flow or regurgitation, and hypoplastic ascending aorta. Retrograde flow in the transverse aortic arch strongly suggests inadequate systemic output from the left heart. Tricuspid regurgitation is common and increases the chance for the development of hydrops. Other findings may be helpful, including left ventricular hyperechoic endocardium and increased nuchal translucency at 11-14 weeks. With careful fetal echocardiography, HLHS may be readily observed on a 4-chamber view as either a small or even absent left ventricle.

Reference ranges for two-dimensional echocardiographic examination of the fetal ductus arteriosus

OBJECTIVES

To establish reference ranges for 2D-echocardiographic examination of the fetal ductus arteriosus and its relationship to the main pulmonary artery and the aorta.

METHODS

A prospective cross-sectional echocardiographic study was performed in 222 normal fetuses from 13 to 41 weeks of gestation using high resolution/color Doppler ultrasound equipment.

RESULTS

Gestational age-specific reference ranges are given for the diameter of the pulmonary valve anulus, diameter of the ductus arteriosus at its beginning, middle, and end, ductal length, ductal diameter-to-pulmonary valve anulus diameter ratio, and the spatial relationship of the ductus arteriosus to the main pulmonary artery and to the aorta.

CONCLUSIONS

The presented data derived from a study group of 222 normal fetuses provide in-vivo insights into the morphology of the ductus arteriosus and its relationship to the adjacent vessels. The reference ranges may be helpful in prenatal diagnosis of cardiac malformations and abnormalities of the ductus arteriosus, such as obstruction or aneurysm from 13 to 41 weeks of gestation.

The application of color power angiography to the longitudinal quantification of blood flow volume in the fetal middle cerebral arteries, ascending aorta, descending aorta, and renal arteries during gestation

OBJECTIVE

This study was undertaken to determine by means of color power angiography the longitudinal changes in the diameters and the flow volumes of 4 major fetal arteries during gestation.

STUDY DESIGN

The middle cerebral artery, the ascending aorta, the descending aorta, and the renal arteries in 81 appropriate-for-gestational-age fetuses were examined longitudinally between 24 and 38 weeks' gestation by means of color power angiography. In addition to measurement of the diameters of these arteries, Doppler velocimetry was performed. Flow volume was calculated from the cross-sectional areas of the arteries and the velocity integral of the Doppler waveforms.

RESULTS

The mean (+/-SD) gestational age at delivery and birth weight were 39.8 +/- 1. 6 weeks and 3326 +/- 345 g, respectively. The diameters and flow volumes of all the arteries increased significantly as gestational age advanced. Flow volume increased from 39 +/- 19.0 mL/min to 140 +/- 63.9 mL/min in the middle cerebral artery, from 216.2 +/- 77.6 to 937.4 mL/min in the ascending aorta, from 124.4 +/- 76.6 to 390.0 mL/min in the descending aorta, and from 27.5 +/- 16.8 to 80.3 +/- 57.3 mL/min in the renal arteries. When blood flow volume was adjusted to milliliters per kilogram body weight, an initial significant fall in blood flow was seen in all the vessels to a minimal level at 30 weeks' gestation; blood flow rose thereafter, although not significantly, until term. The ratios of flow volume in the ascending aorta to those in the other vessels increased with gestation, with the highest ratio being that between the ascending aorta and the renal arteries.

CONCLUSION

Identification of fetal arteries with color power angiography is easy and highly sensitive. The distributions of blood flow in various fetal arteries exhibited regional differences, with significantly more blood flow to the brain. These normative baseline values may be useful in the diagnosis of congenital cardiac anomalies and also in the diagnosis and monitoring of fetuses with intrauterine growth restriction.

The fetal heart: a practical sonographic approach

Structural abnormalities of the heart are a fairly common problem, affecting more than 8 of 1,000 newborns annually in the United States. Therefore, sonographic detection of these anomalies in utero is important. It is possible to detect a high percentage of fetal cardiac anomalies through proper sonographic examination using three central views of the heart: (1) the four-chamber view; (2) the aortic outflow tract view; and (3) the pulmonary output tract view. Although average sonologists may not be able to provide a precise diagnosis for a cardiac abnormality, they are able to recognize such abnormalities in a high percentage of cases by using these three views and by answering the following questions: (1) Is the heart in a normal position? (2) Is the heart size normal? (3) Are the ventricles equal in size? (4) Is there a septal defect? (5) Are the atrioventricular valves in a normal position? and (6) Is there any abnormality of the endocardium, myocardium, or pericardium? This article presents a practical approach to the detection of fetal cardiac anomalies using the four-chamber and outflow tract views. Examples of normal anatomy and cardiac pathology are provided as well as a listing of differential diagnoses that should be reviewed when certain abnormalities are visualized.

Flow velocity profile of the fetal aortic isthmus through normal gestation

Experimental and clinical evidence have demonstrated that an increase in resistance to placental blood flow causes changes in aortic isthmic diastolic flow profile before any significant modification is observed in umbilical artery Doppler waveforms. To identify these abnormal flow profiles, the objective of this study was to document the normal flow profile in the aortic isthmus throughout pregnancy. The study included 81 normal fetuses from 17 to 39 weeks of gestation. On the isthmic flow profile, an index, named the balance index, was calculated: (peak systolic--end-diastolic velocities/forward--reverse flow velocity integrals). Before 20 weeks of gestation, a forward flow was recorded throughout the cardiac cycle and the diastolic deceleration phase was gradual and smooth. After 20 weeks, an incisura appeared at end-systole that progressively increased, and by 30 weeks of gestation a brief reverse diastolic flow was constantly recorded. The balance index increased slightly throughout gestation. Color flow mapping demonstrated that the reverse flow observed late in gestation in the isthmus was coming from the ductus arteriosus. In conclusion, the morphology of the Doppler flow velocity waveform of the fetal aortic isthmus changes with gestation. The proposed balance index may be useful in identifying fetuses with disturbed peripheral hemodynamics.

Assessment of changes in blood flow through the lungs and foramen ovale in the normal human fetus with gestational age: a prospective Doppler echocardiographic study

OBJECTIVE

To measure lung blood flow and flow through the foramen ovale in the normal human fetus and to assess the changes in each with gestational age and the proportions of combined ventricular output that the respective flows represent.

PATIENTS AND DESIGN

38 normal fetuses (gestational age 18-37 weeks) were studied prospectively with Doppler echocardiography.

METHODS

Echocardiographic images and Doppler velocity signals were obtained from the ascending aorta, main pulmonary artery, and ductus arteriosus from each fetus and digitised to obtain arterial diameters, heart rates, and velocity-time integrals. Blood flow in each artery was calculated as the product of heart rate, flow-velocity integral, and arterial cross sectional area. Blood flow through the lung was assessed as the difference between flow in the pulmonary artery and ductal flow; combined ventricular output as the sum of aortic and pulmonary artery flows; and flow through the foramen ovale as the difference between flows through the aorta and lungs.

RESULTS

Blood flow through the lungs increased exponentially with gestational age (r = 0.89, p < 0.001), by almost four-fold over the period of gestation studied, and was a mean (SD) of 22% (7%) of combined ventricular output. Blood flow through the foramen ovale increased exponentially by threefold (r = 0.77, p < 0.001), representing between 17% and 31% of combined ventricular output.

CONCLUSIONS

Blood flow through the lungs and across the foramen ovale can be calculated non-invasively in the normal human fetus. Both flows increase exponentially with age and comprise between one fifth and one quarter of the combined ventricular output, proportions that remain unchanged through the second and third trimesters of pregnancy.

Relationship between fetal pulmonary trunk and ductus arteriosus flow velocity waveforms in early normal pregnancy

To establish the relationship between flow velocity waveform patterns from the fetal pulmonary trunk and ductus arteriosus in normal late first- and second-trimester pregnancies, Doppler ultrasound examinations in these vessels were performed in 133 healthy women between 9 and 25 weeks of gestation. Differentiation between pulmonary and ductal blood flow was possible as from 12 weeks onwards resulting in a study population of 78 women. A linear gestational age-dependent increase in peak systolic velocity was found for both the pulmonary trunk and the ductus arteriosus. Ductal peak systolic velocity rose significantly faster with gestational age than pulmonary peak systolic velocity. This may be determined by differences in morphology and effective lumen between these two vessels.

Assessment of right and left ventricular function in terms of force development with gestational age in the normal human fetus

OBJECTIVE

To assess right and left ventricular systolic function in normal human fetuses by cross sectional Doppler echocardiography to calculate the force developed by myocardial shortening.

DESIGN

Cross sectional echocardiographic images of the aorta and pulmonary arteries were obtained prospectively in order to measure great vessel diameters and calculate their cross sectional areas. Doppler velocity signals were recorded from the proximal aorta and the proximal pulmonary artery and digitised to obtain peak velocity, acceleration time, flow velocity time integral during acceleration, and the flow velocity time integral for the whole of ejection. Right and left ventricular force development was estimated by Newton's equation in which force is defined as the product of mass and acceleration.

PATIENTS

58 normal human fetuses at a gestational age of from 20 to 42 weeks.

RESULTS

The cross sectional area of the pulmonary artery was 20% greater than that of the aorta. Aortic acceleration time was longer than that in the pulmonary artery, and peak blood flow velocity in the aorta was consistently greater than that in the pulmonary artery. Right ventricular stroke volume was significantly greater than left ventricular stroke volume. The force developed by the right and left ventricles was, however, similar throughout the gestational period studied, increasing tenfold from 20 weeks' gestation to term (r = 0.74, p less than 0.0001; r = 0.75, p less than 0.0001) respectively.

CONCLUSION

The development of right and left ventricular force in the human fetus is similar in spite of the greater volume handled by the right ventricle. This index of ventricular performance does not require calculation of ventricular volume and because it varies independently of ventricular geometry and heart rate it should prove useful in assessing cardiac function in the normal human fetus and in fetuses with ventricular dysfunction.

Pulmonary-to-aorta diameter ratio in the normal and abnormal fetal heart

In an attempt to establish the normal ratio of pulmonary artery to aorta diameters at varying gestational ages, the pulmonary artery and aorta diameters of 316 normally grown fetuses between 14 and 39 weeks' gestational age were measured. The ratios for each fetus were derived, and regression analysis was used to evaluate the relationship between gestational age and each diameter. We conclude that the diameters of the pulmonary artery and aorta are closely related to fetal age but that the ratio is independent of age (mean, 1.09; SD, 0.17). The diameters of the pulmonary artery and aorta in 21 fetuses with proved congenital heart disease were then compared with those of this normal population. The pulmonary artery/aorta ratio was abnormal in 13 of 21 fetuses with congenital heart disease. Actual measurements of the great vessels can be difficult and may be misleading, but a quick comparison of relative size by inspection is feasible.

Reproducibility of ultrasonic measurement of fetal cardiac haemodynamics

Two observers made independent estimates of volume flow across all four heart valves in 27 fetuses using a combination of cross-sectional and Doppler echocardiography. There were considerable discrepancies between observers in volume flow estimation arising from inconsistency both in cross-sectional and in Doppler measurements. One observer also produced a second estimate by making new measurements from the original recordings. There was considerable within-observer variability which was mainly due to errors in cross-sectional measurements. The problems of applying this technique to fetal cardiac haemodynamics are discussed.