G. Rizzo

Doppler echocardiographic assessment of atrioventricular velocity waveforms in normal and small‐for‐gestational‐age fetuses

Summary. A prospective longitudinal study determined the physiological patterns of blood flow velocity waveforms in normal and in small‐for‐gestational‐age (SGA) fetuses. Using a Pulsed Doppler Duplex system, 125 normally grown fetuses and 35 SGA fetuses were studied longitudinally at between 27 and 42 weeks gestation. In normal fetuses the ratio between the E velocity (early passive ventricular filling) and the A velocity (active ventricular filling during atrial contraction) increased progressively during pregnancy in both transmitral and transtricuspid waveforms, approaching 1 at term. In SGA fetuses, the E/A ratios did not increase during pregnancy and the values obtained were significantly lower than in normal fetuses. The ratio between the transtricuspid and transmitral mean temporal velocities remained almost constant throughout pregnancy in the normal fetuses with transtricuspid velocity slightly exceeding the transmitral velocity. On the other hand, in SGA fetuses the ratio between the mean temporal velocities was inversed with the transmitral velocity progressively greater than the transtricuspid velocity suggesting the existence of intracardiac hacmodynamic changes in these fetuses.

Utero-placental blood flow velocity waveforms as predictors of pregnancy-induced hypertension

Sixty high-risk pregnancies were studied in order to define the validity of the analysis of utero-placental blood flow velocity waveforms in early screening for developing hypertensive diseases. Recordings were obtained at 18-20 weeks gestation, in normotensive patients, using a pulsed duplex Doppler system at the level of uterine vessels. The patients (n = 22) who developed hypertension showed a higher resistance index value (p less than 0.001) than normotensive patients (n = 38). The validity of uteroplacental waveform analysis was as follows: specificity = 84.2%; sensitivity = 63.6%; positive predictive value = 70%; negative predictive value = 80%; accuracy = 76.6%. The high specificity attained suggests that this test can adequately identify, among a high-risk population, patients destined to remain normotensive during pregnancy.

Behavioural state transitions in healthy and growth retarded fetuses.

The transitions, i.e. time intervals between two different behavioural states, were studied in 10 healthy and 10 growth retarded fetuses (IUGR) in near term pregnancies. In healthy fetuses, transitions usually lasted less than 3 min whereas IUGR fetuses showed a longer duration when compared to healthy fetuses. Moreover, a significant trend in the change of state variables (fetal heart rate, fetal eye movements and fetal gross body movements) was evident in healthy fetuses: fetal heart rate was the first variable to change in transitions from 1F to 2F and the last variable to change in transitions from 2F to 1F. On the other hand IUGR fetuses showed a random sequence in order of change. These findings were substantiated by the intraindividual consistency evidenced in repeated recordings. In conclusion the analysis of transitions differentiates between healthy fetuses and those affected by IUGR.

Short-term effects of maternal oxygen administration on blood flow velocity waveforms in healthy and growth-retarded fetuses

To determine whether maternal oxygen administration affects fetal hemodynamics, we investigated 10 healthy fetuses and 10 growth-retarded fetuses near term by means of Doppler ultrasonography. The growth-retarded fetuses were characterized by abnormal blood flow velocity waveforms. Velocity waveforms were simultaneously recorded at 5-minute intervals from the fetal descending aorta and internal carotid artery before, during, and after maternal oxygen administered through a face mask that delivered 60% oxygen. The pulsatility index was calculated. During oxygen treatment growth-retarded fetuses showed significant temporary hemodynamic modifications as expressed by changes of pulsatility index values that increased in the internal carotid artery and decreased at the level of the descending aorta. On the other side no changes were found in healthy fetuses. These findings suggest that maternal oxygen administration can modify fetal hemodynamics in cases of growth retardation associated with abnormal blood flow velocity waveforms.

Doppler echocardiographic assessment of time to peak velocity in the aorta and pulmonary artery of small for gestational age fetuses.

Summary. The time to peak velocity was measured at the level of the ascending aorta and pulmonary artery by Doppler echocardiography in 38 small‐for‐gestational age (SGA) fetuses before and during maternal hyperoxygenation. The values were compared to a reference range derived from the study of 142 appropriate‐for‐gestational age (AGA) fetuses. In the SGA fetuses the time to peak velocity at the level of pulmonary artery was significantly lower and at the level of the aorta significantly higher than in AGA fetuses. During maternal hyperoxygenation the aortic time to peak velocity decreased towards normal range but there was no significant change at the level of the pulmonary artery. These results may indicate variations of aortic and pulmonary pressures in SGA fetuses that can be partially modified by maternal hyperoxygenation and which may be associated with changes in the peripheral resistance of the cerebral circulation.

Effects of intravascular fetal blood transfusion on fetal intracardiac Doppler velocity waveforms.

In 12 fetuses from pregnancies with red blood cell isoimmunization Doppler velocity waveforms were recorded at the level of atrioventricular valves immediately before and at 15-minute intervals for 2 hours after the intravascular transfusion. The left and right cardiac outputs, the ratio between the peak velocities during early passive ventricular filling and active atrial filling at the level of both ventricles as well as the heart rate were calculated. Before transfusion, the left and right cardiac outputs were significantly higher than reference ranges for gestation that were constructed from the cross-sectional study of 187 normal pregnancies. After transfusion there was a significant temporary fall in right and left outputs associated with increased ratios between the peak velocities during early passive ventricular filling and active atrial filling. Within 2 hours after transfusion both parameters returned toward the normal range. In addition, no significant changes were found for fetal heart rate values before and after transfusion. The fall of cardiac output was significantly related to the amount of expansion of the feto-placental volume.

Placental vascularization measured by three‐dimensional power Doppler ultrasound at 11 to 13 + 6 weeks' gestation in normal and aneuploid fetuses

To establish the potential role of three‐dimensional (3D) power Doppler evaluation of the placental circulation in aneuploidy screening at 11 to 13 + 6 weeks of gestation.

Functional assessment of uteroplacental and fetal circulations by means of color Doppler ultrasonography

A study was made in order to assess whether the combined use of color flow mapping and conventional pulsed Doppler could improve the accuracy of blood flow velocity waveform analysis in fetal and placental circulations. Fifty patients were studied at 18 to 20 or 26 to 28 weeks of gestation by two trained investigators by means of either conventional Doppler or conventional Doppler plus color flow mapping. Recordings were performed at the level of the uterine arteries, umbilical artery, descending aorta, and internal carotid artery. The experimental procedure was repeated the following day with the patients undergoing the alternate technique of recording. In all the vascular districts investigated, color flow mapping allowed us to obtain a higher number of reliable recordings, to shorten the observation time, and to reduce the intra‐ and interobserver coefficient of variations.

Prenatal cerebral Doppler ultrasonography and neonatal neurologic outcome.

The significance of fetal cerebral blood flow analysis in the prediction of neonatal neurologic outcome was investigated on 87 fetuses at risk for chronic hypoxia. Blood flow velocity waveforms were recorded from the fetal internal carotid artery immediately before cesarean section; newborns underwent neurologic follow‐up until discharged from the neonatal division. Neonatal outcome was considered abnormal in presence of a postasphyxial encephalopathy. Receiver operating characteristic curves were used to demonstrate the efficacy of fetal cerebral blood flow velocity waveform analysis as a predictor of neonatal outcome. A value of the pulsatility index from the internal carotid artery below the second standard deviation of our range of normality was found to be a powerful indicator of the development of neonatal neurologic abnormalities (Cohens Kappa index = .58). These results were particularly evident in fetuses with a birthweight above 2500 g in which a specificity of 93.7%, a sensitivity of 75%, and an accuracy of 89.7% were achieved.

Low cardiac output to the placenta: an early hemodynamic adaptive mechanism in intrauterine growth restriction

A low combined cardiac output (CCO) to the placenta (placenta/CCO fraction) has been reported in growth‐restricted (IUGR) fetuses, but the temporal sequence of these modifications in relation to other changes in the fetal circulation is unknown. The aim of this study was to evaluate the placenta/CCO fraction in relation to other hemodynamic changes in fetuses at risk of developing IUGR.