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.     

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.     

Blood flow in the fetal descending aorta

Doppler estimation of the blood flow in the descending aorta of the fetus and waveform analysis of the maximum aortic velocity provide valuable information on fetal circulation. When estimating fetal aortic flow, it is important to consider possible sources of error; even when recording the maximum aortic velocity for waveform analysis, to obtain reproducible results it is important to use a low high-pass filter, a well-defined angle of insonation, and a standardized site of measurement and to avoid periods of fetal breathing and activity. In normal pregnancy the time-averaged mean velocity in the descending aorta is stable throughout the third trimester. The weight-related flow is stable until 37 weeks, after which it falls slightly. The placental proportion of the flow in the thoracic descending aorta decreases toward term. In the aorta of normal fetuses there is positive flow throughout the whole heart cycle, which is due to the low vascular resistance in the placental circulation. The waveform of the aortic velocity can be characterized by the PI, which is stable during the last trimester of gestation. Caution is required when interpreting changes in the aortic PI, as it is not only affected by the peripheral resistance but also by the heart performance. Furthermore, PI is related to fetal heart rate. Near term different values of PI are found in different fetal behavioral states. In fetuses with retarded growth and in fetuses at distress, characteristic changes of the aortic velocity waveform have been reported by several researchers: the end-diastolic velocity diminishes and disappears, and in extreme cases a brief reversal of flow in diastole was observed. Consequently, the PI increases in such cases. The absence of the end-diastolic aortic velocity can easily be determined and is the best indicator of fetal status: in fetuses with absent end-diastolic velocity the incidence of perinatal mortality and morbidity is significantly higher than in fetuses with positive flow throughout the cycle. In pregnancies with hypertension or diabetes mellitus, normal aortic flow has been reported, as long as the fetuses were not growth retarded. In cases of severe Rh-isoimmunization, the mean aortic velocity correlates with fetal hematocrit. In hypoxic fetuses the mean velocity was reported to correlate with the degree of hypoxia, hypercarbia, and acidosis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Doppler ultrasound assessment of cerebral blood flow in the human fetus

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.     

Color-Doppler for predicting vascular resistance to feto-placental blood flow and fetal well-being

Aloka Color-Doppler, model SSD-860, was used to observe the blood velocity waveforms in the umbilical artery and in the fetal descending thoracic aorta in 139 normal pregnant women from 16th to 40th week and 30 patients suffering from pregnancy induced hypertension (PIH syndrome). The ratio of systolic to diastolic peak flow (A/B) reflected the fetoplacental vascular resistance and peripheral resistance. The results demonstrated that the placental resistance in PIH syndrome and IUGR were much higher than that in normal pregnancy. The placental resistance decreased when patients condition improved after treatment and vice versa. This suggests that fetal blood velocity waveforms (FVW) is of great value in the intensive monitoring of IUGR fetuses. The blood velocity FVW was also of great value in evaluating the curative effects on PIH patients.     

Normative values of Doppler velocimetry of five major fetal arteries as determined by color power angiography

OBJECTIVE: To produce normograms of Doppler indices of major fetal arteries and their ratios relative to the ascending aorta in a cohort of appropriately grown for gestational age fetuses. METHODS: Prospective longitudinal study of 70 women with appropriately grown for gestational age fetuses between 24 and 38 weeks' gestation attending the Fetal Growth Clinic of a large UK teaching hospital. Doppler velocimetry of the middle cerebral (MCA), umbilical (UmA) and renal arteries (RA) and the ascending (AAO) and descending (DAO) aortas were studied using color power angiography. Ratios of the Doppler indices [pulsatility index (PI), resistance index (RI), systolic/diastolic (S/D) ratio] were then calculated using the ascending aorta as the reference numerator for the other four vessels to produce normograms. Regression analysis was performed to determined the significance, if any, of the changes in these ratios with gestation. RESULTS: The normograms of the various Doppler indices were similar for the middle cerebral artery, ascending and descending aortas. There was an initial rise to a peak between 30 and 32 weeks and then a gradual return to values at 38 weeks similar to those at 24 weeks' gestation. In the renal artery, the indices showed very little variation with gestation. However, there was a gradual fall in the indices with gestation in the umbilical artery. The ratios of the various indices relative to that of the ascending aorta demonstrated an increase with gestation. The changes with gestation were statistically significant for the ratios of the indices from the ascending aorta to those of the middle cerebral, renal and umbilical arteries but not for those of the descending aorta. CONCLUSIONS: The vascular resistance in the five fetal arteries decreased towards the end of pregnancy and the ratios of their indices relative to those of the ascending aorta decreased from 24 to 38 weeks' gestation. Early subtle changes in circulation in compromised fetuses may be identified early from deviations in these normograms.     

Perinatal outcome in fetuses with loss of end-diastolic blood flow velocities in the descending aorta and/or umbilical arteries.

Continuous- and pulsed-wave Doppler velocimetry was used as an additional method of antenatal surveillance in high-risk pregnancy care. During a 30-month period with 4,169 deliveries 226 patients (5.4%) with complicated pregnancies (intrauterine growth retardation, diabetes, hypertension) were investigated. The results had only marginal influence on obstetrical management. In 38 fetuses absence of end-diastolic blood flow velocities (AEDF) was detected in the descending fetal aorta and/or umbilical arteries. Mean birth weight of these fetuses was 1,441 +/- (SD) 690 g at a mean gestational age of 31.8 +/- 6.8 weeks at birth. Twenty fetuses (53%) were growth-retarded (less than 3rd centile). Six fetuses died in utero and 7 during the perinatal period (34% mortality). There was a significant deterioration of perinatal outcome with AEDF in the umbilical arteries at the last antenatal Doppler scan. With AEDF in the descending fetal aorta the Doppler parameter Vmean and with AEDF in the umbilical arteries the pulsatility index yielded additional prognostic information. Doppler velocimetry of the fetal and umbilical vascular system could be of additional value for antenatal surveillance in high-risk pregnancies.     

Evaluation of the renal artery in the fetuses with growth retardation and oligohydramnios by two dimensional Doppler ultrasonography

Renal blood flow dynamics were studied with color and pulsed Doppler ultrasound in 102 normal fetuses at 20 to 40 weeks of gestation, 11 growth retarded fetuses (group A), 15 fetuses with oligohydramnios (group B) and 10 growth retarded and oligohydramniotic fetuses (group C) at 32-40 weeks of gestation. The maximum systolic velocity (VMAX), early diastolic peak velocity (VEA), end diastolic velocity (VED) and resistance index (RIEA:VMAX-VEA/VMAX and RIED:VMAX-VED/VMAX) were measured in the renal artery. VMAX was also measured in the ascending aorta (AO) and pulmonary artery (PA). In the normal fetuses, blood flow velocity increased with gestational age, but VMAX and VEA remained constant after 28 weeks of gestation. The resistance index decreased with gestational age, but RIEA remained constant after 28 weeks of gestation. RIED in groups A and C increased significantly, and VMAX in groups B and C, and VED in group C decreased significantly compared with normal fetuses. VMAX in AO and PA decreased remarkably in the three abnormal groups. It was concluded that the kidneys were poorly perfused in the growth retarded fetuses with oligohydramnios, which may, in part, depend on the decreased stroke volume.     

Labetalol does not alter the placental and fetal blood flow or maternal prostanoids in pre-eclampsia

The effect of intravenously administered labetalol (1 mg/kg) on placental and fetal blood flow was studied in 13 pre-eclamptic women. Although the maternal blood pressure decreased, no changes occurred in the blood flows in the intervillous space, the umbilical vein or the fetal descending aorta, nor did the indices of peripheral vascular resistance in the fetal aorta change, but the placental vascular resistance did decrease. Labetalol had no effect on prostacyclin or thromboxane A2 as measured by urinary 6-keto-prostaglandin F1 alpha and serum thromboxane B2 respectively. These findings are clinically relevant since they suggest that labetalol reduces maternal blood pressure without interfering with the placental or fetal blood flow.     

Influence of nicotine chewing gum on fetal blood flow

Several studies have shown that smoking is not beneficial to the fetus. Among the acute effects, influence on fetal circulation has been reported. Nicotine is considered to be one of the active agents in cigarette smoke. To test the nicotine effects on the human fetus, maternal and fetal cardiovascular dynamics were studied in 20 pregnant women when chewing a chewing gum containing 4 mg of nicotine and a chewing gum without nicotine given in a randomized double blind order. The fetal blood flow was measured with a method combining real-time ultrasonography and pulsed Doppler technique. Registrations were made in ten fetuses from the thoracic part of the descending aorta and in ten fetuses from the intra-abdominal part of the umbilical vein. In 15 of the fetuses registrations were also made from the umbilical artery. Concentrations of nicotine in plasma were analyzed in six women. The maternal plasma nicotine concentrations increased after the nicotine gum to a maximum value of 12.4 ng X ml-1 (median) at 25 min (figure 1). The 4 mg nicotine gum increased significantly maternal heart rate, systolic and diastolic blood pressure (figure 2). There was no influence on fetal heart rate or fetal blood flow, neither in the thoracic part of the descending aorta, nor in the intra-abdominal part of the umbilical vein (figure 3). There were no changes in the waveforms of the maximum blood velocity curves, neither of the aorta nor the umbilical artery. This indicates that there was no increased resistance in the placenta, neither after the nicotine gum nor the placebo gum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of echocardiographic parameters by fetal behaviour

In order to verify if fetal behavioural states could affect cardiac parameters, thirty-one healthy fetuses were studied near term. We evaluated systolic time intervals (pre-ejection period and ventricular ejection time), M-mode parameters (fractional shortening and mean circumferential shortening) and Doppler flow velocities (mean peak velocity of aortic and pulmonary arteries) of left and right ventricles. Both fetal breathing movements and fetal heart rate patterns seem to modify these parameters with an increase of cardiac contractility during active phases of fetal behaviour.     

Labetalol does not alter the placental and fetal blood flow or maternal prostanoids in pre-eclampsia

Summary. The effect of intravenously administered labetalol (1 mg/kg) on placental and fetal blood flow was studied in 13 pre-eclamptic women. Although the maternal blood pressure decreased, no changes occurred in the blood flows in the intervillous space, the umbilical vein or the fetal descending aorta, nor did the indices of peripheral vascular resistance in the fetal aorta change, but the placental vascular resistance did decrease. Labetalol had no effect on prostacyclin or thromboxane A₂ as measured by urinary 6-keto-prostaglandin F_1α and serum thromboxane B₂ respectively. These findings are clinically relevant since they suggest that labetalol reduces maternal blood pressure without interfering with the placental or fetal blood flow.     

The blood flow velocity waveform in the fetal internal carotid and umbilical artery; its relation to fetal behavioural states in normal pregnancy at 37-38 weeks

The relation between the blood flow velocity waveform in the fetal internal carotid artery (n = 12) and umbilical artery (n = 15) and fetal behavioural states at 37-38 weeks of gestation was studied. In the fetal internal carotid artery, under standardized fetal heart rate conditions, the pulsatility index (PI), as a measure of peripheral vascular resistance, was significantly lower during behavioural state 2F (active sleep) compared with state 1F (quiet sleep) according to the classification by Nijhuis et al. (1982), suggesting increased fetal cerebral blood flow during state 2F. In the umbilical artery, no significant difference in PI between the two behavioural states could be established. This suggests a fetal origin of the state dependency observed in fetal blood flow velocity waveforms.     

Nuchal translucency thickness and fetal cardiac flow velocity in normal fetuses at 11-13 weeks of gestation

OBJECTIVE: To investigate the relationship between nuchal translucency thickness and cardiac flow velocity in normal fetuses at 11-13 weeks of gestation. Subjects and METHODS: Eighteen normal pregnancies were prospectively studied with transvaginal sonography and pulsed and color Doppler ultrasound. Flow velocities at the fetal atrioventricular valves (mitral and tricuspid valve) and outflow tract levels (ascending aorta and pulmonary artery), and at the descending aorta were recorded. Nuchal translucency thickness was also measured. RESULTS: Mitral peak velocity during early diastolic filling correlated with gestational age. Mitral peak velocities during early diastolic filling and atrial contraction, tricuspid peak velocity during early diastolic filling, ascending aorta peak velocity, and pulmonary artery peak velocity correlated well with nuchal translucency thickness. There was an inverse correlation between umbilical artery pulsatility index and gestational age. CONCLUSIONS: These results suggest that the increase of nuchal translucency thickness in normal fetuses at 11-13 weeks of gestation may be the consequence of changes in fetal cardiac functions.     

Fetal blood flow in diabetic pregnancy

Forty pregnant diabetic women were examined with combined Doppler and real-time ultrasound. The volume blood flow in the fetal aorta and umbilical vein was higher and the pulsatility index (PI) in the aorta lower in the early third trimester, as compared with a reference group. Near term, the umbilical artery PI was higher in diabetic than in non-diabetic pregnancies, indicating a higher placental vascular resistance in the former group. The high umbilical artery PI occurred in fetuses who later developed distress in labor. Therefore, a high umbilical artery PI cannot be considered characteristic of diabetic pregnancy, although fetal distress might be more common in diabetic pregnancy. In addition, a high aortic volume flow was found in those fetuses who later develop distress in labor. This might be an expression of an early compensatory mechanism for increased placental vascular resistance. No specific flow variation was observed for any White class, or in association with hypertension or non-optimally regulated diabetes. The blood flow variables in growth-accelerated fetuses were comparable to those found in fetuses with normal weight. Since fetal distress might be more common in diabetic pregnancy, ultrasonic fetal blood flow measurements are recommended for antenatal fetal surveillance.     

Fetal and uteroplacental haemodynamics during short-term atenolol treatment of hypertension in pregnancy

Fetal circulation was studied by means of combined real-time and pulsed Doppler ultrasound in 14 women with pregnancy-associated hypertension before and during the first and third days of treatment with the beta 1-selective blocker, atenolol; in seven of the women the maternal uterine arcuate blood velocity waveform was also studied. Blood flow characteristics were normal both in the fetus and in the maternal arcuate artery, compared with those in uncomplicated pregnancies of corresponding gestational ages. Volume blood flow remained unchanged in the fetal descending aorta, and in the umbilical vein during atenolol treatment, whereas the pulsatility index increased in the fetal descending aorta and in the arcuate artery. This suggests that the peripheral vascular resistance, both on the maternal and fetal side of the placenta, increased during short-term antihypertensive treatment with atenolol.     

The development of fetal behavioural states: a longitudinal study

In order to evaluate the development of fetal behavioural states a longitudinal study was performed on 35 healthy fetuses during the last trimester of pregnancy. Fetal heart rate (FHR), gross fetal body movements (FM), fetal eye movements (FEM), fetal breathing movements (FBM) and micturition were simultaneously studied at two-week intervals from 28 weeks gestation onwards. Well-defined fetal behavioural states were observed only after 36 weeks gestation. Between 28 and 36 weeks the quiet-activity cycle of FHR was always detected and some fetal biophysical activities seemed to become related around this cycle.     

Fetal behaviour in type-1 diabetic women

Real-time ultrasound observation of fetal movement patterns can be used to assess the development of the motor component of the nervous system. Data are presented on the emergence of fetal movements in the first trimester of pregnancy, and on the development of fetal behavioural states in the third trimester, in women with type-1 (insulin dependent) diabetes. In the first trimester there is a delay in emergence of movement patterns. This delay is, however, not specific but parallels that of growth. In the third trimester there is a delay in emergence of fetal behavioural states. It is concluded that a tight metabolic control, achieved with continuous insulin infusion, does not prevent these disturbances in development.     

Doppler blood flow waveforms in the descending thoracic aorta of the human fetus

Summary. A linear-array pulsed Doppler duplex has been used to study third-trimester Doppler flow velocity waveforms (FVW) in the descending thoracic aorta of 98 normal and 20 severely growth-retarded fetuses. Waveforms have been normalized (frequency index profile; FIP) to remove the effect of the angle of insonation and so allow comparison at different gestational ages and with complicated pregnancies. There is an increase in end-diastolic velocities with advancing gestational age indicating a reduction in placental resistance. The growth-retarded fetuses showed a significant reduction in end-diastolic velocities and an increase in the pulsatility index (normal PI: mean 1.83, SD 0.22; growth-retarded PI: mean 2.78, SD 0.60). This reduction of diastolic blood flow may indicate reduced placental vascularity and predict impending fetal hypoxia.     

Doppler blood flow waveforms in the descending thoracic aorta of the human fetus

A linear-array pulsed Doppler duplex has been used to study third-trimester Doppler flow velocity waveforms (FVW) in the descending thoracic aorta of 98 normal and 20 severely growth-retarded fetuses. Waveforms have been normalized (frequency index profile; FIP) to remove the effect of the angle of insonation and so allow comparison at different gestational ages and with complicated pregnancies. There is an increase in end-diastolic velocities with advancing gestational age indicating a reduction in placental resistance. The growth-retarded fetuses showed a significant reduction in end-diastolic velocities and an increase in the pulsatility index (normal PI: mean 1.83, SD 0.22; growth-retarded PI: mean 2.78, SD 0.60). This reduction of diastolic blood flow may indicate reduced placental vascularity and predict impending fetal hypoxia.