B.J. Trudinger

Fetal umbilical artery velocity waveforms and subsequent neonatal outcome

Summary. Flow velocity waveforms (FVWs) from the fetal umbilical artery were recorded from 2178 pregnant women over a 6‐year period. All of them had an obstetric factor indicating increased risk of fetal compromise. A total of 6749 studies was recorded. The systolic diastolic (AB) ratio was measured and classified as normal (<95th centile), elevated (95–99th centile), high (>99th centile) or extreme (absent diastolic flow). The results of these studies have been related to subsequent fetal and neonatal outcome. An abnormal umbilical artery FVW was associated with shorter gestation and infants with lower birthweight, shorter length and lower ponderal index. There was a highly significant association between an abnormal FVW and the birth of an infant small for gestational age. The significance of the association increased with the increased abnormality of the umbilical artery FVW and this was independent of gestational age. Preterm infants associated with high or extreme AB ratios spent twice as long in the neonatal nursery than those with normal AB ratios. Analysis of 794 pregnancies studies serially indicated that an abnormal FVW in which the AB ratio was increasing, in contrast to a decreasing AB ratio, predicted a poor outcome for both size at birth and duration of neonatal intensive care. We conclude that in high risk pregnancy Doppler umbilical artery FVW studies predict the most compromised fetuses in terms of growth retardation and requirements for neonatal intensive care.

UMBILICAL ARTERY FLOW VELOCITY WAVEFORMS IN HIGH-RISK PREGNANCY: Randomised Controlled Trial

300 patients at high fetal risk (mean gestational age 34 wk) were randomised to a group for antenatal doppler umbilical artery waveform studies and a control group. The timing of delivery was similar in the control and doppler-report-available groups overall. However, in the report group obstetricians allowed the pregnancies of those not selected for elective delivery to continue longer. There was no difference in the rates for elective delivery (induction of labour or caesarean section) in the two groups, whereas among those who went into labour (induced or spontaneous) emergency caesarean section was more frequent in the control group (23%) than in the report group (13%). Fetal distress in labour was also more common in the control group. Babies from the control group spent longer in neonatal intensive care (level 3) and needed more respiratory support than did those in the report group. The findings indicate that the availability of doppler studies leads to better obstetrical decision making.

A comparison of Doppler ultrasound waveform indices in the umbilical artery—I. Indices derived from the maximum velocity waveform

Various Doppler waveform indices have been used for assessment of the fetal circulation. Comparisons were made to show what relations exist between the indices, and to identify any differences or difficulties which might arise from using one as opposed to another in clinical practice. Both normal pregnancy and cases of fetal growth failure were studied. Indices were obtained from the maximum velocity envelope of the umbilical artery waveform using a curve fitting technique. The values were very reproducible for all indices. The FHR, which varied over the entire normal range, did not significantly affect the values of any index. The downstream impedance indices calculated included the AB ratio, pulsatility index (PI) and Pourcelot ratio. These all gave very closely correlated results for normals but discrepancies occurred in the at risk group, where values were elevated. This could be attributed to differences in the underlying distributions. The indices suggested for cardiac contractility were not as closely related to each other, and moreover the differences between them showed no clear pattern. None of the indices varied independently of the others. The rising slope, which is by definition related to the PI, was more highly correlated with the downstream indices than the relative flow rate index.

Doppler ultrasound waveforms in the fetal umbilical artery: Quantitative analysis technique

Doppler ultrasound waveforms from the fetal umbilical artery were analyzed by a new quantitative technique. Normal pregnancy and cases of fetal growth failure were considered. Data from the spectrum analyzer were dumped to a microcomputer, the velocity waveforms calculated and a representative waveform obtained by ensemble averaging. This curve was then fitted by a 4-parameter analytic function. We introduce R, the relative flow rate index, which measures the ratio of the average flow rate before the systolic peak to the average rate during the remainder of the cardiac cycle. In cases of fetal growth failure this ratio was significantly greater than in normal pregnancy. Other new quantities defined are the normalized systolic decay time index and the constant flow ratio. The AB ratio was also calculated. Fetal growth failure has been associated with raised placental resistance. We suggest that the fetus can initially compensate for this by increasing cardiac contractility. This can be seen by interpreting the R and AB values together. Our analysis technique enables the waveform to be efficiently described, and provides useful diagnostic information about placental function and fetal wellbeing.

A comparison of Doppler ultrasound waveform indices in the umbilical artery—II. Indices derived from the mean velocity and first moment waveforms

Umbilical artery Doppler recordings in both normal pregnancy and cases of fetal growth failure were processed by computer. Representative waveforms for the maximum velocity, mean velocity and first moment were obtained after ensemble averaging and correction for thump filtering. The same set of indices, which included the AB ratio, pulsatility index, rising slope and relative flow rate index, were calculated for each of the waveforms. The results were compared to identify differences which might arise in clinical practice if a waveform other than the usual (maximum velocity) was used. The ratio of the mean to the maximum velocity, which gives an indication of the velocity profile, was shown to be very error prone. The reproducibility of the mean velocity and first moment indices was inferior to that of the maximum velocity indices. The results from the different waveforms were highly correlated for normals for most indices. However, in the growth retarded group there was a tendency for the mean velocity and first moment indices to classify as normal studies classified as abnormal by the maximum velocity index. The values of indices derived from the first moment waveform were generally larger than the maximum and mean velocity values. For the relative flow rate index, where results were often different to the general trend, the values were more nearly equal.

Aortic Doppler velocity measurement and cardiac function in the fetal lamb

Aortic haemodynamic parameters, and Doppler waveforms in particular, were investigated in acute experiments with fetal lambs. Cardiovascular changes were produced by central infusion of the drugs esmolol and dopamine. Pulsed Doppler waveforms were obtained from the descending thoracic aorta, simultaneous with recordings of pulsatile aortic volume flow rate, diameter and blood pressure. The relation between Doppler-derived velocities and the corresponding full vessel lumen velocities was shown to be fairly linear and consistent across different animals. The aortic volume flow per beat decreased with esmolol (p < 0.003, repeated measures ANOVA); the Doppler and vessel lumen mean velocities also decreased, whether measured only at peak systole or over the full cardiac cycle (at most p < 0.003). With dopamine the aortic flow per beat increased (p < 0.001), as did the Doppler and vessel lumen mean velocities (at most p < 0.02). An inverse relation between the aortic flow per beat and the peripheral resistance was observed. To identify inotropic changes in the presence of vascular effects, a theoretical model based on cardiac power output changes was implemented. The data were divided into three groups, according to whether the model did or did not identify a definite inotropic effect (positive or negative). The Doppler velocity changes for these three groups were different (p < 0.0001). The mean Doppler velocity increased by 7 cm s-1 in the positive inotropic effect group, and decreased by 4 cm s-1 in the negative group. The aortic flow parameters of the human fetus are very similar to those of the fetal lamb.(ABSTRACT TRUNCATED AT 250 WORDS)

Egr-1 transcription activation exists in placental endothelium when vascular disease is present

Objective  To seek evidence of early vascular injury in the placental villous microcirculation in placental insufficiency identified by a high‐resistance umbilical Doppler study by examining for expression of fibroblast growth factor receptor‐1 (FGFR‐1), its transcription factor, early growth response factor‐1 (Egr‐1) and plasma fibroblast growth factor‐2 (FGF‐2).

OP02.09: Measurement of cardiac contractility using fetal isovolumetric contraction time in fetal anemia caused by Rhesus alloimmunization

Objectives: We examined the influence of fetal anemia seen in Rh alloimmunization on cardiac contractility as measured by the isovolumetric contraction time (ICT). The ICT is the time interval between the onset of the ventricular contraction and cardiac ejection. It is an index of cardiac contractility. This may be measured with a Doppler approach using appropriate frequency digital filters to distinguish the movements of the mitral and aortic valves in the Doppler cardiogram. We have previously reported animal validation and a normal range for human fetuses. Methods: Our study was carried out in two parts. (A) In six patients undergoing percutaneous umbilical cord blood sampling (PUBS) to assess the level of fetal hemoglobin (fetal Hb) because of Rh alloimmunization, we measured the fetal ICT with the Doppler technique within 24 hours of PUBS. (B) We carried out 2nd daily measurements of the fetal ICT during the 6-week course of antenatal therapy in a patient receiving three fetal intrauterine blood transfusions because of fetal anemia. Results: (A) In six patients with fetal anemia, there was a significant correlation between the fetal Hb and fetal ICT. The most anemic fetus had the shortest ICT. (B) Serial studies in a patient receiving three intrauterine transfusions demonstrated a shortening of the fetal ICT as the fetus became anemic and after each transfusion, the fetal ICT lengthened back into the ‘normal range’. Conclusions: The ICT measures contractility. The shortened ICT seen in associated with fetal anemia in both our cross-sectional and longitudinal data indicates enhanced cardiac contractility with fetal anemia and we hypothesize that this is a component of the high output state of fetal anemia to maintain oxygen delivery. We did not study any hydropic fetuses but we postulate that a prolonged ICT above our normal range might signal cardiac failure and developing hydrops.