H.M. Tonge

Doppler ultrasound assessment of cerebral blood flow in the human fetus

Summary. A mechanical sector and linear array real‐time scanner combined with a pulsed Doppler system was used for recording the flow velocity waveform in the internal carotid artery, the lower thoracic part of the descending aorta and umbilical artery in the human fetus. A total of 42 fetuses in normal pregnancy and nine growth‐retarded fetuses between 26 and 41 weeks gestation was studied. In normal pregnancy the mean pulsatility index (PI) in the internal carotid artery varied between 1·5 and 1·6, in the descending aorta between 1·7 and 1·8 and in the umbilical artery between 0·7 and 1·3. In the growth‐retarded fetuses the PI was reduced in the internal carotid artery and raised in the descending aorta and umbilical artery, suggesting an increased peripheral vascular resistance in the fetal body and placenta and a compensatory reduction in peripheral vascular resistance in the fetal cerebrum, i.e. a brain‐sparing effect in the presence of fetal hypoxia.

The blood flow velocity waveform in the fetal descending aorta: its relationship to fetal behavioural states in normal pregnancy at 37–38 weeks

In 13 normal pregnancies, the relationship between the blood flow velocity waveform at the lower thoracic level of the fetal descending aorta and fetal behavioural states at 37-38 weeks of gestation was studied. The pulsatility index (PI), as a measure of peripheral vascular resistance, was significantly lower during state 2F compared to state 1F according to the classification by Nijhuis et al. (Nijhuis, J.G. et al. (1982) Early Hum. Dev., 6, 177-195), suggesting an increased perfusion of the fetal skeletal musculature to meet the energy demand needed for the raised muscular activity during state 2F; A significant inverse relationship (P less than 0.001) was established between PI and FHR in state 2F; this was mainly determined by a significant rise in end-diastolic flow velocity (P less than 0.02). Both the behavioural state and FHR should be taken into account when evaluating flow velocity waveforms in the fetal descending aorta during the latter weeks of pregnancy.

Vascular dynamics in the descending aorta of the human fetus in normal late pregnancy

Fetal blood flow velocity and diameter changes in the lower thoracic part of the descending aorta were compared in twenty normal pregnancies between the gestational age of 30 and 41 weeks. The mean blood flow velocity remained constant throughout the study period whereas a significant increase in vessel diameter was observed. The significant increase in aortic stroke volume and blood flow was in correlation with this diameter change.

The blood flow velocity waveform in the fetal descending aorta; its relationship to behavioural states in the growth-retarded fetus at 37-38 weeks of gestation

In 12 patients with intrauterine growth retardation (IUGR), the relationship between the blood flow velocity waveform at the lower thoracic level of the fetal descending aorta and fetal behavioural states at 37-38 wk of gestation was studied. A significant inverse relationship (P less than 0.001) was established between pulsatility index (PI) and fetal heart rate (FHR) in state 1F and 2F. The PI as a measure of peripheral vascular resistance, demonstrated a marked increase compared to normal pregnancy. There is a virtual overlap of PI values originating from state 1F and 2F according to the classification by Nijhuis et al. (J.G. Nijhuis, H.F.R. Prechtl, C.B. Martin, Jr. and R.S.G.M. Bots (1982) Early Hum. Dev. 6, 177-195). The peripheral vasoconstriction present in IUGR seems to overrule state dependent PI fluctuations. The marked rise in PI, particularly at lower FHR and the constancy of PI in relation to fetal behavioural states can be considered vascular adaptations, which are instrumental in the centralization of the fetal circulation, with the aim of favouring blood supply to the brain, heart and adrenals during IUGR.

Fetal blood flow measurements during fetal cardiac arrythmia

3 cases of fetal complete heart block, 1 case of fetal bradycardia and 2 cases of fetal supraventricular tachycardia were studied. Using an ultrasonic technique combining real-time ultrasound with a pulsed Doppler system, blood flow measurements at the lower thoracic level of the fetal descending aorta were taken. Despite alterations in rhythm, the blood flow in the aorta descendens was maintained within normal range. With a reduced heart rate, there was an increase in stroke volume, blood flow velocity, acceleration of blood flow velocity and maximum diameter change; conversely, with an increased heart rate the same four parameters were lowered. These alterations reflect changes in cardiac contraction force, and illustrate the ability of the fetal myocardium in maintaining blood flow in the growing fetus.

The role of diagnostic ultrasound in the study of fetal cardiac abnormalities

Between January 1982 and April 1983, a total of 315 patients was scanned for fetal Congenital Heart Disease (CHD). In 70% of these patients, there was an increased risk for CHD in their offspring, in the remaining 30% abnormal findings were made by ultrasound in the present pregnancy. Nine cardiac defects were correctly diagnosed. There were three false positive and three false negative findings. The presence of fetal dysrhythmia, Intra-Uterine Growth Retardation (IUGR), ascites or polyhydramnios warrants a structural analysis of the fetal heart. Prenatal scanning for CHD should preferably be carried out in centres which can guarantee a high degree of scanning experience, up-to-date scanning equipment and close cooperation with a well-established neonatal and pediatric cardiology unit.

Cardiac ventricular geometry and function in the growth-retarded fetus

M-mode recordings of the fetal cardiac ventricles were studied in 15 pregnant women with fetal growth retardation. Pregnancy duration varied between 28 and 40 weeks of gestation. In the presence of normal fetal heart rate patterns, M-mode assessment of ventricular geometry and function did not provide additional information on fetal condition. A close relationship between left ventricular output and fetal weight could be demonstrated.