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.     

Evaluation of umbilical venous blood flow by Doppler color flow mapping and conventional ultrasonographic methods.

Ultrasonographic measurement of umbilical venous blood flow as a reflection of placental blood flow has been used for assessment of fetal well-being. Because fetal and maternal factors may prevent satisfactory measurement of umbilical venous diameter and flow velocity, an alternative method would be helpful. We found that, in 35 human fetuses between 18 and 35 weeks of gestation, that both variables for umbilical venous flow calculation can be measured from a single Doppler color frame with close measurement agreement to conventional combined cross-sectional pulsed Doppler ultrasonographic measurements. Thus, this method provides an alternative to the conventional method or may be used for a cross-check and has the potential for automated flow calculation.     

Precision and accuracy of Doppler flow measurements. In vitro and in vivo study of the applicability of the method in human fetuses

The precision of the Doppler method for quantitative blood flow measurement in the fetal descending thoracic aorta and in the umbilical vein and for estimation of the Pulsatility Index from the velocity curve from fetal aorta was tested in vivo by examination of six pregnant women eight times. Two investigators examined each patient twice in random order upon two successive days. The diameter of the vessel was measured using planimetry on a magnified time-motion image of the diameter variations during the heart cycle, while the angle between the ultrasound Doppler beam and the vessel of interest was measured on the hard copy image. No systematic variation was found between observers, days, repeated observations or repeated readings of curves and images. The mean coefficient of variations was 5.6% for the quantitative flow per kilogram estimated fetal weight measured in the fetal descending aorta, 6.8% for the quantitative flow per kilogram estimated fetal weight measured in the umbilical vein and 9.8% for the Pulsatility Index. When the diameter of aorta was calculated as the mean of the maximal and the minimal diameter measured on the hard copy image, the mean coefficient of variation for the flow increased to 9.4%. In vitro tests of the Doppler instrument and the real-time scanner revealed a systematic overestimation of Doppler measured flow of only 4.4% compared with the true flow, and a real-time scanner underestimation of vessel diameter of only 1.1%.     

Quantitative blood flow in the fetal descending aorta and in the umbilical vein in normal pregnancies. Longitudinal and cross-sectional studies

Quantitative blood flow in the fetal descending thoracic aorta and in the umbilical vein was measured both in a longitudinal study where each of 13 fetuses was examined three times and in a cross-sectional study where 45 fetuses were examined once only in the last trimester of normal pregnancy. The waveform of the velocity curves from fetal descending aorta was examined and the Pulsatility Index, the A/B ratio and the least diastolic velocity were calculated. The longitudinal study showed that all these parameters and the fraction of the flow in the fetal descending aorta, which was distributed to the placental circulation, were constant during the last trimester. The problems of longitudinal inference from cross-sectional studies are discussed. For all 58 fetuses the flow in the descending thoracic aorta was 234 ml/min/kg and in the umbilical vein 127 ml/min/kg. The Pulsatility Index was 1.83, the A/B ratio 4.75, the least diastolic velocity 9.9 cm/s. The fraction of blood flow in the descending aorta distributed to the placental circulation was 55%.     

Abnormal ductus venosus blood flow: a clue to umbilical cord complication.

We report a case of umbilical cord complication causing, fetal hypoxemia and acidemia. At 30 weeks of gestation, the patient was referred because of slightly increased amniotic fluid volume and a non-reactive cardiotocogram. Biometry was appropriate for gestational age. Umbilical artery and fetal aortic Doppler findings were normal, whereas diastolic blood flow velocities in the middle cerebral artery were increased and the ductus venosus showed severely abnormal flow velocity waveforms with reversal of flow during atrial contraction. Since other reasons for fetal hypoxemia could be excluded, careful examination of the umbilical cord was performed. Traction of the hypercoiled umbilical cord due to its course around the fetal neck and shoulders was suspected. Cesarean section confirmed the sonographic findings and fetal blood gases revealed fetal acidemia. This case indicates that investigation of fetal venous blood flow may also help to identify fetal jeopardy due to reasons other than increased placental vascular resistance.     

Changes in fetal hemodynamics with ritodrine tocolysis.

OBJECTIVE: To evaluate the effect of ritodrine on the fetal cardiovascular system. METHODS: Cardiac and extracardiac Doppler waveforms were recorded in 12 fetuses prior to and during ritodrine therapy used for preterm labor. Maternal and fetal heart rates, the Doppler pulsatility indices of the umbilical artery, middle cerebral artery, descending thoracic aorta and renal artery, and time velocity integrals of the atrioventricular valves and the ductus arteriosus, were measured. RESULTS: Ritodrine infusion caused an increase in maternal and fetal heart rates, the left cardiac output as measured by the product of time velocity integral and heart rate, and the pulsatility index of the middle cerebral artery, and a decrease in the pulsatility index of the umbilical artery. CONCLUSIONS: Ritodrine infusion may alter placental and cerebral blood flow and may have a selective effect on the left side of the heart.     

Assessment of fetal heart rate variability and velocity variability by Doppler velocimetry of the descending aorta at 10-20 weeks of gestation.

OBJECTIVES: Determination of gestational age-related modulations in fetal heart rate and descending aorta blood flow velocity in the early human fetus and comparison of aortic variability data with data obtained from the umbilical artery. It is hypothesized that these modulations present in the umbilical artery also occur in the descending aorta. METHODS: Doppler studies of descending aorta velocity waveforms were performed at 10-20 weeks in 55 normal pregnant women. In 24 of the 55 women, Doppler recordings from both the descending aorta and the umbilical artery were collected. Absolute values and variability of fetal heart rate, peak systolic and time-averaged velocities were determined from flow velocity waveforms of at least 18 s in duration. RESULTS: From 10 to 20 weeks of gestation, the descending aorta peak systolic and time-averaged velocities increased, whereas the fetal heart rate decreased. The descending aorta peak systolic variability also increased. However, the time-averaged velocity variability and fetal heart rate variability remained constant during the study period. In the subset of 24 women, the fetal heart rate variability and velocity variability data from the descending aorta and umbilical artery were not significantly different. CONCLUSIONS: Reproducible fetal heart rate and velocity variability data can be derived from the descending aorta and umbilical artery. The increase in heart rate variability observed in the umbilical artery was not seen in recordings obtained from the descending aorta. Different fetal activity states may be the underlying mechanism for these heart rate variability discrepancies.     

Ultrasonic measurement of fetal blood velocity wave form as a secondary diagnostic test in screening for intrauterine growth retardation

Based on routine fetometry screening at 32 weeks of gestation, 80 out of 3226 singleton pregnancies were suspected of intrauterine growth retardation (IUGR) and 72 of them were subjected to repeated fetal blood flow measurements by Doppler ultrasound for evaluation of the fetal condition. The maximum blood velocity wave form recorded from the fetal descending aorta and umbilical artery was classified as normal or abnormal depending on the presence or absence of positive end-diastolic blood flow. Compared to the pregnancies with normal fetal blood flow, the group of 30 pregnancies with abnormal blood flow patterns had significantly more pregnancy complications and more operative deliveries for fetal distress. In the latter group, all newborns but one were small-for-gestational age and had low 1-min Apgar scores more frequently. Fetal blood flow measurements have a good capacity for predicting unfavorable fetal outcomes and can be recommended for clinical use. The combination of ultrasound screening and Doppler blood flow measurement has reduced the number of pregnancies requiring intensive surveillance.     

Comparison of the prognostic value of pulsed Doppler blood flow parameters to predict SGA and fetal distress.

A total of 219 women with complicated pregnancies had Doppler assessment of uteroplacental arteries, the umbilical artery, the fetal common carotid artery and the descending thoracic aorta to determine the prognostic value of Doppler examinations to predict the birth of a small-for-gestational-age (SGA) infant with or without fetal distress. Preliminary reproducibility studies showed that the resistance index, pulsatility index and intensity weighted flow velocity had the lowest coefficients of variation. Data on the systolic/diastolic ratio and mean blood flow volume were, therefore, not considered for further evaluation.Measurements were classified according to the time interval of the examination to the delivery of the baby according to the following groupings: 0-14 days, 15-28 days and 29-42 days. For evaluation of the SGA fetus complicated by fetal distress, only measurements within 2 weeks of delivery were analyzed. Significant differences were calculated by considering the area below the receiver operator characteristic (ROC) curves.Only Doppler studies of the uteroplacental arteries (mainly resistance index) were predictive of the later development of the SGA fetus. All fetal parameters showed an increasing improvement in the predictive capacity for an SGA infant, the closer the measurements were made to the time of delivery. This improvement was not observed for uteroplacental vessels.The resistance index of the uteroplacental vessels was significantly higher in SGA pregnancies complicated by fetal distress compared to SGA pregnancies alone. However, ROC analysis revealed that fetal Doppler velocimetry was more strongly related to fetal distress than SGA only. The single best fetal parameter was the mean velocity in the fetal descending thoracic aorta but the velocity ratio of the fetal common carotid artery over the fetal descending thoracic aorta had the highest predictive capacity for the SGA pregnancy complicated by fetal distress.     

New implanted Doppler sensors for the assessment of the main fetal hemodynamics.

If the fetal Doppler examination during human pregnancies provides useful information to the obstetrician, it does not allow us to collect all the biological and haemodynamic data required to understand the physiopathological mechanisms involved in the development of intrauterine growth retardation (IUGR) and hypoxia. With the animal model, it is possible to have access to the blood pressure, the blood velocity and volume, to collect blood sampling and to perform pharmacological tests, or to simulate some human pathology. Several studies have been already carried out on lamb fetuses using electromagnetic flowmeters placed around the cord and catheters, with pressure sensors placed inside the fetal aorta. Most of the time only the umbilical flow was assessed on the fetal side. The aim of the present work was to develop a new Doppler system able to monitor in real time and simultaneously, the fetal cerebral and the umbilical arterial flows as well as the uterine circulation. New flat Doppler probes have been designed, to be implanted on the fetus and on the mother, which makes possible the atraumatic assessment of fetal and maternal flows during approximately 20 days. The 4-MHz CW Doppler probe consists of two rectangular piezoelectric transducers of 13-mm wide, preoriented at 45 degrees from the surface of the probe, placed in a 6-mm-high plastic case in which small holes are made to sew the probe on the fetal skin. The sensors are fixed on the fetal skin, facing the umbilical cord, the fetal cerebral arteries and in front of the uterine arteries.(ABSTRACT TRUNCATED AT 250 WORDS)     

Doppler-derived umbilical artery absolute velocities and their relationship to fetoplacental volume blood flow: a longitudinal study.

OBJECTIVES: To construct reference ranges for serial measurements of the umbilical artery (UA) absolute blood flow velocities in the second half of pregnancy and to test the hypothesis that significant associations exist between UA velocities and placental volume blood flow assessed from umbilical vein blood flow velocities and diameter. METHODS: This was a prospective longitudinal study of the umbilical circulation. UA absolute velocities and umbilical vein blood flow were measured at 4-weekly intervals between 19 and 42 weeks' gestation in 130 low-risk singleton pregnancies. A total of 511 observations were used to construct the reference ranges and assess the association between UA absolute velocities and placental volume flow using multilevel modeling. RESULTS: Both UA absolute velocities and placental volume blood flow showed a steady increase throughout the second half of pregnancy. However, the gestational age-related increase in the UA end-diastolic velocity (EDV) was greater than the corresponding increase in the peak systolic velocity (PSV). The time-averaged intensity-weighted mean velocity (TAWMV)/time-averaged maximum velocity (TAMXV) was 0.6 indicating probably not a completely parabolic velocity profile. There was a significant positive association (P < 0.00001) between UA absolute velocities and placental volume blood flow, but this association was modified by the gestational age. The intraobserver coefficients of variation for the UA PSV, EDV, TAMXV and TAWMV and placental volume blood flow were 10.17%, 16.29%, 11.46%, 18.18% and 8.61%, respectively. CONCLUSION: We have established new reference ranges for the UA absolute velocities based on longitudinal data. They show a significant association with fetoplacental volume blood flow and may have a clinical value in the assessment of the umbilical circulation.     

Blood flow in the fetal descending aorta; intrinsic factors affecting fetal blood flow, i.e. fetal breathing movements and cardiac arrhythmia

An ultrasonic method combining real-time ultrasonography and pulsed Doppler technique was used for the examination of blood flow in the fetal descending aorta. The mean aortic blood flow velocity in the last trimester of normal pregnancies was 29.0 cm/s; the peak maximum velocity 97.3 cm/s and the mean blood flow 238.4 ml/min/kg. The blood flow velocity did not change significantly with gestational age, the aorta diameter showed a linear growth. During labour, the aortic blood flow in undistressed fetuses was not different from the flow recorded during late pregnancy. Fetal breathing movements modulate the flow velocity signals in the descending aorta, the inferior vena cava and the umbilical vein of the fetus; therefore, when quantifying fetal blood flow, only periods without fetal breathing movements should be considered. A group of fetuses with various types of cardiac arrhythmias was examined. Postextrasystolic potentiation was found to be present already during intrauterine life. The present method enables quantitative evaluation of the hemodynamic effects of cardiac arrhythmias.     

Doppler ultrasound measurements in the central circulation of anesthetized fetal sheep during obstruction of umbilical-placental blood flow.

OBJECTIVE: To establish by Doppler ultrasound the effects of acute blockage of umbilical cord vessels on the fetal central circulation. DESIGN: Experimental study in anesthetized pregnant sheep. METHODS: In 11 anesthetized pregnant sheep (0.66 of gestation), Doppler velocity profiles and/or venous flow rates were recorded in the ductus venosus, the fetal aorta, the umbilical arteries and the umbilical vein. This involved three phases. In Phase 1, the abdominal wall was closed (n = 9); Phase 2 was during fetoscopy after laparotomy (n = 8); Phase 3 was after coagulation of one of the umbilical arteries (n = 10). As an additional intervention in six fetuses, the umbilical cord was clamped for 5-15 s while blood flow velocity changes in the ductus venosus were observed. RESULTS: There were no significant differences between Doppler recordings in Phases 1 and 2. During Phase 3, the pulsatility index of the aorta and of the coagulated umbilical artery increased significantly. The umbilical vein blood flow rate was significantly reduced from a median of 408 (range, 243-575) mL/min/kg in Phase 1 to a median of 173 (range, 107-426) mL/min/kg in Phase 3, but the blood flow rate in the ductus venosus (median, 94; range, 56-148 mL/min/kg vs. median, 92; range, 33-237 mL/min/kg) remained unchanged. The ductus venosus/umbilical vein ratio increased from a median of 0.22 (range, 0.13-0.41) to 0.56 (range, 0.17-0.97) (P < 0.05). Compression of the cord (5-15 s) immediately reduced the time averaged maximum velocity in the ductus venosus from a mean of 51 (standard deviation, 11) cm/s to 20 (standard deviation, 6) cm/s (P < 0.001) without significant changes of the velocity profile. However, the pulsatility index increased from a mean of 0.55 (standard deviation, 0.19) to 1.89 (standard deviation, 0.73) (P < 0.001). CONCLUSION: Central venous flows in anesthetized fetal sheep are unaffected by laparotomy and hysterotomy. Obliteration of one umbilical artery increases the ductus venosus/umbilical vein volume flow (mL/min/kg) ratio. Compression of the umbilical cord shifts down blood flow velocity profiles in the ductus venosus, and the pulsatility index thus increases.     

多普勒超声对高原地区胎儿脐动脉血流的研究

目的运用多普勒超声测量高原地区正常妊娠胎儿脐动脉血流,观察高原环境对胎儿脐带胎盘循环的影响。方法随机选取在外院(海拔2300 m)进行产前检查的正常妊娠孕妇103例为高原观察组,随机选取同期在我院(海拔44 m)进行产前检查的正常妊娠孕妇216例为平原对照组。高原组与平原组均按照孕周分为五组:20~23+6周、24~27+6周、28~31+6周、32~35+6周、36~40周,运用多普勒超声对两组胎儿脐动脉血流搏动指数(PI)、阻力指数(RI)、收缩期峰值流速与舒张末期流速比值(S/D)进行测定。结果孕中晚期五组中,高原组与平原组正常妊娠胎儿PI、RI和S/D差异均无统计学意义(P>0.05)。结论海拔2300 m高原地区正常妊娠胎儿脐带胎盘循环阻力与平原地区无明显差异。     

Doppler assessment of the normal early fetal circulation.

Combined transvaginal and transabdominal Doppler ultrasound allows recording of fetal intra- and extracardiac flow velocity waveforms in late first- and early second- trimester pregnancies. At 10-12 weeks, end-diastolic flow velocities were always absent in the fetal descending aorta and umbilical artery, but were present in over half of the intracerebral artery waveforms. The pulsatility index in the three vessels decreased significantly with advancing gestational age, suggesting a reduction in fetal and umbilical placental vascular resistance. Peak velocities during atrial contraction (A-wave) were nearly twice as high as those during early diastolic filling (E-wave), reflecting low ventricular compliance. Continuous forward flow in the umbilical vein was associated with a pulsatile systolic and diastolic forward flow in the ductus venosus. Retrograde flow was only present in the inferior vena cava.     

Uteroplacental circulation in growth retardation--experiences with the clinical use of continuous-wave Doppler]

Doppler ultrasound measurement of blood flow velocity represents a non-invasive method of studying uteroplacental and feto-placental haemodynamics. Using a continuous-wave Doppler device, the blood flow velocity was examined in the uterine and arcuate arteries, as well as in the umbilical artery in 81 patients demonstrating fetal growth retardation. An increase in vessel resistance was found in the uterine and arcuate arteries in most of the patients. In addition, patients with fetal retardation showed a significantly higher rate of diastolic notching and incomplete registration of uterine and arcuate wave forms, especially in pregnancies complicated by hypertension. The implementation of the continuous-wave technique as a simple Doppler system allows differential evaluation of placental function and provides information on the nutritional supply to the fetus.     

Doppler velocimetry and the assessment of fetal well-being in normal and diabetic pregnancies.

Doppler ultrasound has been proposed as a useful addition to antepartum testing in high-risk pregnancies. Increased placental resistance has been associated with underlying placental vascular disease, as well as abnormal fetoplacental blood flow. Since pregnancies complicated by diabetes are at risk for these complications, the application of Doppler ultrasonography for such pregnancies has been evaluated by several investigators.Multiple investigations have examined the relationship between maternal blood glucose levels and abnormal Doppler waveforms in women with diabetes. Of the nine published studies, four found a correlation between Doppler indices and glucose control, as measured by mean blood glucose levels and glycosylated hemoglobin levels, while five did not. However, this apparent discrepancy may be explained by the fact that the majority of women studied were in good or excellent control, as this is currently the accepted standard of care. In fact, the one study performed in primarily non-diabetic women demonstrated that increases in maternal plasma glucose concentrations of 30 mg/dl were followed by significant rises in the mean pulsatility index in both the umbilical and carotid arteries. More dramatic was the finding by most investigators that systolic/diastolic (S/D) ratios in third-trimester umbilical arteries were elevated in women with evidence of diabetic microvascular disease. Elevated third-trimester S/D ratios were associated with adverse maternal and perinatal outcomes in these women, specifically pre-eclampsia and intrauterine growth retardation.In conclusion, although elevated Doppler indices correlated with adverse outcomes in diabetic pregnancies, Doppler indices may be elevated in the otherwise uncomplicated diabetic patient with associated microvascular disease and with a normal outcome. Therefore, the Doppler ultrasound assessment of fetal well-being in diabetic pregnancies must be interpreted with caution.     

应用多普勒超声观测胎儿肝内门脉系统的血流改变

目的　应用多普勒超声测出胎儿时期肝内门脉系统的血流参数。方法　应用EUB 5 65A型彩色多普勒诊断仪检测 5 0例胎儿门脉主干、门脉右支、门脉左支囊部及静脉导管和 5 0例胎儿脐静脉的平均血流速度及流量。结果　各血管血流速度的顺序是静脉导管 >脐静脉 >门脉主干及其左、右支 (P <0 .0 5 ) ,血流量的顺序是脐静脉 >门脉左支 >门脉主干>静脉导管 (P <0 .0 5 )。结论　多普勒超声是评价胎儿门静脉系统血流的最佳方法     

Power spectrum analysis of heart rate and blood flow velocity variability measured in the umbilical and uterine arteries in early pregnancy: a comparative study.

OBJECTIVE: To compare power spectral derived variability parameters from the fetal side of the placental circulation with those from the maternal side of the placental circulation, during early pregnancy. METHODS: Doppler velocity waveforms were obtained from both the umbilical and the uterine arteries in a study group of 40 pregnant women between 10 and 14 (n = 25) and 15 and 20 (n = 15) weeks of gestation. The coefficient of variation of both the beat-to-beat heart rate variability and the blood flow velocity variability was determined. The ratio of the integrated low-frequency components (< 0.2 Hz) and the integrated high-frequency components (> 0.2 Hz) from normalized power spectrum analysis (LH-ratio) was established, to reflect sympathovagal balance. RESULTS: The coefficient of variation and LH-ratio of fetal heart rate variability constitute only a fraction of the same maternal heart rate variability parameters. Nevertheless a highly significant increase (P < 0.001) in LH-ratio was demonstrated with advancing gestational age. The coefficient of variation and LH-ratio of blood flow velocity variability were significantly lower in the fetal umbilical artery only in the 10-14-weeks' gestation group. Due to a decrease of the maternal uterine blood flow velocity variability parameters with advancing gestational age, statistically equal fetal and maternal values for coefficient of variation and LH-ratio were found in the 15-20 weeks' gestation group. CONCLUSIONS: The increase in LH-ratio of fetal heart rate variability indicates functional development of the fetal autonomic nervous system at 15-20 weeks' gestation. The umbilical blood flow velocity variability may be secondary to maternal uterine arterial flow variability rather than due to primary changes in fetal cardiovascular function.     

Serial sonographic findings of four fetuses with homozygous alpha-thalassemia-1 from 21 weeks onwards.

OBJECTIVES: To evaluate the potential usefulness of noninvasive ultrasound assessment of fetal anemia in the diagnosis and management of fetuses with homozygous alpha-thalassemia-1. METHODS: We describe four pregnancies complicated by fetal homozygous alpha-thalassemia-1. They presented with ultrasound abnormalities before the development of hydrops. As part of evaluating the fetal condition, we performed ultrasound and Doppler studies aimed at identifying fetal anemia. These studies included evaluation of intrahepatic umbilical venous maximum flow velocity, middle cerebral artery peak flow velocity, fetal liver length and spleen perimeter. RESULTS: In all four fetuses, ultrasound and Doppler studies suggested the presence of fetal anemia. Homozygous alpha-thalassemia-1 was diagnosed in all cases, with fetal blood sampling confirming anemia in three fetuses. The majority of the intrahepatic umbilical venous maximum flow velocity and middle cerebral artery peak flow velocity measurements were above the 95th centile. Two fetuses underwent intrauterine transfusion and fetal blood flow velocities returned to normal after correction of the fetal anemia. The fetal liver length and spleen perimeter measurements showed a similar trend, although they were less consistent before 28 weeks. CONCLUSION: Non-invasive ultrasound parameters, in particular quantification of intrahepatic umbilical venous maximum flow velocity and middle cerebral artery peak flow velocity, were found to be useful in the diagnosis and management of fetal anemia in pregnancies with fetal homozygous alpha-thalassemia-1.