Reproducibility of ultrasonic measurement of fetal cardiac haemodynamics

Fetal cardiac output and its distribution to the placenta at 11-20 weeks of gestation

OBJECTIVES

To measure serial changes in cardiac output (CO) and its fraction distributed to the placenta at 11-20 weeks of gestation.

METHODS

Blood flow velocities, and diameters of the aorta, pulmonary artery and umbilical vein, were measured longitudinally in 143 fetuses using pulsed-wave Doppler and two-dimensional ultrasound examination.

RESULTS

Volume blood flow of the aorta (left ventricular CO) and the pulmonary artery (right ventricular CO) increased in a similar manner with advancing gestational age. The combined cardiac output (CCO) increased from 9 mL/min to 121 mL/min, and the placental volume blood flow (Q(uv)) increased from 1.2 mL/min to 25.3 mL/min during 11-20 weeks of gestation. The fraction of CCO diverted to the placenta increased from 14% at 11 weeks to 21% at 20 weeks.

CONCLUSIONS

We have established longitudinal reference ranges for fetal CO and Q(uv) at 11-20 weeks of gestation. The fraction of CCO distributed to the placenta increased significantly during this period, reflecting rapid placental growth and establishment of a low-resistance circulation.

Fetal cardiac output in monochorionic twins

OBJECTIVES

To compare fetal cardiac output (CO) in donor and recipient twins of twin-twin transfusion syndrome (TTTS) pregnancies after laser therapy with that of monochorionic twins without TTTS and normal singletons.

METHODS

In a longitudinal, prospective study, we sonographically assessed fetal CO in donors (n = 10) and recipients (n = 10) with TTTS after fetoscopic laser therapy, in monochorionic twins without TTTS (n = 20) and in normal singleton pregnancies (n = 20). The fetal CO of TTTS twins was determined 1 day and 1 week after laser treatment, and from then on every 2-4 weeks until birth. Twins without TTTS were examined biweekly until birth. Singletons were examined twice, with an 8-week interval, at different gestational ages between 17 and 35 weeks.

RESULTS

Absolute CO increased exponentially with advancing gestational age (P < 0.0001), and was significantly related to fetal weight in all groups (P < 0.0001). The median CO/kg in donors after laser therapy, recipients after laser therapy and non-TTTS monochorionic twins was significantly higher than that in singletons (all P < 0.001). Median CO/kg in donors after laser therapy, recipients after laser therapy, and non-TTTS monochorionic twins was not significantly different between groups.

CONCLUSIONS

Monochorionic twins with TTTS have higher CO after laser therapy than normal singletons.

Fetal Myocardial Thickening Measured by Ultrasonic-Based Technique Called ‘Phased-Tracking Method’

OBJECTIVE

To evaluate fetal myocardial movement by using newly developed ultrasonic technique.

METHODS

We analyzed 50 normal fetuses between 25 and 41 weeks' gestation for changes in thickness of fetal myocardium using the phased-tracking method, a technique with high vertical distance resolution and the potential to evaluate fine ventricular wall movements. We analyzed differences in the rate of change in ventricular wall thickness and in changes in the inner and outer wall layers with advancing gestation. We also analyzed myocardial thickening period and evaluated the ratio of increasing thickness period to stroke interval.

RESULTS

Mean thickness changing rate was significantly higher in the right (1.18 +/- 0.34 m/s/m) than in the left ventricular wall (0.86 +/-0.31 m/s/m) (p < 0.001). Mean ratio of increasing thickness period to stroke interval was significantly higher in the right (0.57 +/- 0.064) than in the left ventricle (0.46 +/- 0.075) (p < 0.001), indicating that myocardial contraction in the fetal right ventricle predominates. The thickness-changing rate of the bilateral ventricular walls was positively and linearly correlated with gestational age. The myocardial-wall thickness-changing rate was higher in the outer layer than in the inner layer in late gestation.

CONCLUSIONS

We conclude that measurement of the thickness-changing rate of fetal ventricular walls using the phased-tracking method might be useful for evaluation of fetal cardiac function.

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.

Repeatability of echocardiographic measurements in the human fetus

OBJECTIVES

To determine the repeatability of cross-sectional, M-mode and Doppler echocardiographic measurements in the human fetus.

METHODS

This was a prospective echocardiographic study of 10 normal fetuses, involving measurement of 32 different echocardiographic variables in each. The intra- and interobserver error of measurements were quantified. The median (range) gestational age was 23 (17-34) weeks.

RESULTS

Cross-sectional echocardiography: for left ventricular end-diastolic volume the intraobserver coefficient of variation was 13% and the interobserver limits of agreement were a ratio of 0.46-2.19. For left ventricular ejection fraction the repeatability was +/- 8.8% and the interobserver limits of agreement were +/- 20%. M-mode echocardiography: the coefficient of variation for left ventricular end-diastolic dimension was 10%, and the interobserver limits of agreement were a ratio of 0.74-1.70. The intraobserver repeatability of left ventricular fractional shortening was +/- 8.8%, and interobserver limits of agreement +/-15%. Limits of agreement for M-mode-derived left ventricular end-diastolic volume were wide, intraobserver coefficient of variation 32% and interobserver limits were a ratio of 0.44-4.36. Doppler echocardiography: the intra- and interobserver errors were high for Doppler variables such as acceleration time, acceleration slope, stroke volume, cardiac output and vessel dimension. There was less error associated with measurements such as maximum Doppler velocity, velocity time integral, ejection time and heart rate.

CONCLUSIONS

The repeatability of most echocardiographic measurements in the fetus is poor. This applies particularly to volumetric data such as ventricular volumes and volume flow estimations. Interobserver errors are consistently higher than intraobserver errors, confirming that when sequential measurements are clinically important, the same observer should be used.

Fetal cardiac function and septal thickness in diabetic pregnancy: a controlled observational and reproducibility study

OBJECTIVE

To determine the reproducibility of duplex Doppler waveform analysis and fetal cardiac interventricular septal thickness measurement and to compare these parameters in matched pregnancies with and without well-controlled maternal Type 1 diabetes at 18-20 weeks of gestation.

DESIGN

A prospective blind twin cohort study and a blinded inter-observer and intra-observer agreement study.

SETTING

A tertiary referral prenatal diagnostic unit within a university hospital.

RESULTS

Good inter- and intra-observer agreement was found for the measurement of transvalvular peak flow velocities and the duration of ventricular ejection in the fetal heart. Inter-observer agreement for aortic flow acceleration rate was poor. M-mode measurement of interventricular septal thickness showed moderate reproducibility. The mean (SD) width of the interventricular septum in the fetuses of well controlled diabetic women was 2 1 mm (0.2 mm), and was significantly greater (P=0.01) when compared with the corresponding value in matched controls [1.9 mm (0.2 mm)]. No cardiac functional differences were evident.

CONCLUSIONS

On-screen video analysis of Doppler cardiac flow waveforms and M-mode measurement of intraventricular septal thickness demonstrated good reproducibility. The fetuses of well controlled diabetic pregnancies demonstrated signs of altered cardiac morphology early in pregnancy, before any evident alterations in cardiac function.

Antibody mediated complete congenital heart block in the fetus

Complete congenital heart block (CCHB) affects 1:20,000-25,000 live births and is usually an atrioventricular block; 30-50% of fetuses with CCHB will have a structural anomaly, though recently attention has focused on the etiological influence of autoimmune disease, such as systemic lupus-erythematosus. The diagnosis is established by detailed two-dimensional ultrasound scanning of the heart to exclude anomaly coupled with M-mode echocardiography and Doppler blood velocity patterns in the major vessels to detect the uncoupling of atrial and ventricular rhythms. Risk factors for an affected child are discussed. A previously affected child, high titers of anti-Ro antibodies, the presence of anti-Ro (SS-A) and anti-La (SS-B), and maternal HLA DR3 confer high risk. Antibody mediated CCHB is irreversible. Plasmapheresis and immunosuppression have been attempted in affected mothers, with limited success, to reduce the likelihood of the fetus being affected, and steroids have been used to reduce the inflammatory reaction in the heart. In many cases the underlying pathology of the immune system adversely affects utero-placental function requiring careful monitoring of fetal well-being. CCHB renders fetal heart rate monitoring virtually useless, in the antenatal and intrapartum periods. Alternatives are explored.