Are blood flow velocity waveforms related to umbilical cord acid-base status in the human fetus?

Doppler blood flow velocity waveforms from fetal umbilical artery, descending aorta, internal carotid artery and maternal uterine arteries were recorded in 50 fetuses near term undergoing cesarean section before the onset of labor in order to evidence eventual relationships with the fetal acid-base status. The primary indications for cesarean section were in 16 cases an elective repeated cesarean section and in the remaining cases maternal hypertension often associated with fetal growth retardation and/or fetal distress. The technique of anesthesia was strictly standardized and fetal blood gas levels and acid-base status were analyzed in umbilical artery and vein immediately after birth. A significant correlation was found between the pulsatility index from internal carotid artery and the pO2 levels in umbilical vein (r = 0.87; p less than or equal to 0.001). Similar relationships were found between the pulsatility index from descending aorta and the pCO2 (r = 0.78; p less than or equal to 0.001), base excess (r = 0.72; p less than or equal to 0.001) and pH (r = 0.80; p less than or equal to 0.001) levels in umbilical artery. It is suggested that Doppler ultrasound could be useful in the diagnosis of fetal hypoxia and acidosis.     

Changes in the umbilical venous blood flow of human fetus in labor

In the present study, we intended to depict the changes occurring during labor in the fetal umbilical blood flow. Simultaneously, we also investigated the characteristics of the changes and their relation to the fetal heart rate patterns. In 15 human labors, the blood flow velocity in the intra-abdominal part of the umbilical vein was recorded continuously by the pulsed Doppler ultrasound technique. At the same time, direct fetal ECG and uterine contraction were monitored. The umbilical venous blood flow during the uterine contraction was equal to or lower than that between the uterine contractions. The maximum umbilical blood flow was decreased by 50% or more at variable deceleration and reduction of the umbilical venous blood flow was followed by a decrease in heart rate. Otherwise at late deceleration, the umbilical venous blood flow reduction was not so marked and biphasic pulsation became evident following the heart rate decrease. The present study has revealed that the umbilical venous blood flow shows characteristic patterns at variable deceleration and late deceleration.     

Ultrasonic measurement of aortic and umbilical blood flow in the human fetus

The study reports blood velocity and blood flow in the descending aorta and the umbilical vein of 20 normal human fetuses by application of combined B-mode ultrasound and pulsed Doppler technique. All pregnancies and newborns were clinically normal. The echographic examination was performed between 37 and 40 weeks' gestation by an ADR real-time linear scanner 2130 coupled with the Kranzb uhler pulsed Doppler system 8105. The diameter of the vessels was measured by B-mode echogram, and the Doppler beam was directed to form an incident angle between 30 and 65 degrees with the axis of the vessel. The Doppler shift frequency was measured electronically with a spectrum analyzer 8106. Fetal blood velocity waveforms were calculated following the Doppler equation. In the descending aorta, the calculated velocity was 27.7 +/- 6.7 cm/second (mean +/- SD) and the blood flow was 679 +/- 106 ml/minute or 216 ml/kg/minute. In the umbilical vein, the same parameters were 18.3 +/- 4.0 cm/second, 366 +/- 65 ml/minute, and 117 +/- 16 ml/kg/minute, respectively. The average umbilical flow: aortic flow ratio was 0.54 +/- 0.07.     

The effect of immediate delivery on the fetus with reverse end-diastolic flow velocity in umbilical artery velocimetry]

Reverse end-diastolic flow velocity suggests a catastrophic fetal condition. Some authors have suggested that perinatal management of these pregnancies should be more aggressive. Despite increased opportunities to use Doppler ultrasonography, guidelines for clinical management of such pregnancies have not been established. We have applied immediate delivery to 6 patients out of 7 patients who showed reverse end-diastolic flow velocity. When the study population was compared with the population of the other authors, there were no differences in gestational age at diagnosis, birth weight, or incidence of maternal hypertension. However, the study patients were delivered at significantly higher Apgar scores and had a lower perinatal mortality rate. These results suggest that immediate delivery of the fetus with reverse end-diastolic flow may be correlated with a favorable perinatal outcome.     

Longitudinal assessment of blood flow velocity waveforms in the healthy human fetus

A longitudinal study was carried out on 30 healthy fetuses in order to assess the modifications of fetal blood flow throughout pregnancy. The pulsatility index was evaluated at two-week intervals by means of pulsed Doppler equipment. In the umbilical artery measurements were performed from 20 weeks onwards, whereas in the descending aorta and internal carotid artery analysis started from 26 weeks onwards. A decrease of the pulsatility index in umbilical artery and in the ratio between the pulsatility indexes in umbilical artery and internal carotid artery was found over the second half of pregnancy.     

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Summary. Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time wave-forms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (<90 μm diameter) in the tertiary stem villi in a standard microscopic field (mean 18·5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1–2 arteries/field) than in both the normal and control groups (7–8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.     

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time waveforms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (less than 90 micron diameter) in the tertiary stem villi in a standard microscopic field (mean 18.5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1-2 arteries/field) than in both the normal and control groups (7-8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.     

Relationship of umbilical vein blood flow to growth parameters in the human fetus.

OBJECTIVE: Our purposes were to determine the relationship of the growth of umbilical blood flow to growth in body measurements of human fetuses in uncomplicated pregnancies. The study also aimed to assess the relative contributions of growth in umbilical vein diameter and of increased velocity to the increase in umbilical blood flow. STUDY DESIGN: An animal study was conducted to assess the accuracy of umbilical vein blood flow measurements obtained by triplex mode ultrasonography. Seven pregnant ewes underwent triplex mode umbilical vein flow determination. These results were compared with historical flow data obtained by a steady-state diffusion technique in 34 ewes matched for gestational age and weight. In a separate study performed on human beings, reproducibility and precision of triplex mode flow determination were assessed, as were the relationships between umbilical vein flow and gestational age and head and abdominal circumferences. This cross-sectional study was performed with 70 healthy fetuses ranging from 20 weeks' gestation to term. Best-fit interpolating equations and confidence limits were calculated for blood flow measurements versus gestational age and head and abdominal circumferences. RESULTS: In the validation study performed on sheep there were no significant differences between triplex mode and steady-state measurement groups with respect to gestational age or weight. The umbilical vein flows were similar between triplex mode and steady-state measurement groups (P =.881). In the human study the intraobserver and interobserver coefficients of variation for the vein diameter, mean velocity, and absolute umbilical vein blood flow varied from 2.9% to 12.7%. The mean duration of examination was 3 +/- 1 minutes. The umbilical vein diameter and mean velocity increased throughout pregnancy. The absolute umbilical vein flow increased exponentially from 97.3 mL/min at midgestation to 529.1 mL/min at 38 weeks' gestation, whereas umbilical vein flow per kilogram of fetal weight did not change significantly with gestational age. There was a strong correlation between absolute umbilical vein flow and the fetal head and abdominal circumferences. CONCLUSIONS: The triplex mode ultrasonographic technique can play an innovative role in obtaining quick and reproducible measurements of umbilical vein blood flow. The approach was validated with a sheep model. Umbilical vein blood normalized for fetal weight (milliliters per minute per kilogram of fetal weight) and absolute flow (in milliliters per minute) are consistent with previous human studies. We have established new reference values of umbilical vein blood flow relative to head and abdominal circumferences. The growth of umbilical venous diameter accounted for most of the growth in umbilical vein flow.     

Umbilical cord whole blood viscosity and the umbilical artery flow velocity time waveforms: a correlation

The possibility was examined of an association between umbilical cord whole blood viscosity and umbilical artery flow velocity time waveforms obtained with continuous wave Doppler ultrasound. The cord blood viscosity was measured at both high (100 s-1) and low (0.1 s-1) shear rates with a concentric cylinder viscometer. Plasma viscosity and fibrinogen were also measured. An abnormal pattern in the umbilical artery flow velocity waveform (high A/B ratio) indicative of high resistance was associated with an increase in whole blood viscosity at high shear (which may reflect a change in red cell rigidity). Viscosity at low shear (reflecting red cell aggregation and rouleaux formation) did not differ. There was a significant association between the small-for-gestational age fetus and abnormal umbilical artery waveform study (P less than 0.002) but not abnormal whole blood viscosity at high (P = 0.09) or low (P = 0.08) shear.     

Umbilical cord whole blood viscosity and the umbilical artery flow velocity time waveforms: a correlation

Summary. The possibility was examined of an association between umbilical cord whole blood viscosity and umbilical artery flow velocity time waveforms obtained with continuous wave Doppler ultrasound. The cord blood viscosity was measured at both high (100 s^−l) and low (0·1 s^−I) shear rates with a concentric cylinder viscometer. Plasma viscosity and fibrinogen were also measured. An abnormal pattern in the umbilical artery flow velocity waveform (high A/B ratio) indicative of high resistance was associated with an increase in whole blood viscosity at high shear (which may reflect a change in red cell rigidity). Viscosity at low shear (reflecting red cell aggregation and rouleaux formation) did not differ. There was a significant association between the small-for-gestational age fetus and abnormal umbilical artery waveform study ( P <0·002) but not abnormal whole blood viscosity at high ( P =0·09) or low ( P =0·08) shear.     

Umbilical cord whole blood viscosity and the umbilical artery flow velocity time waveforms: a correlation

Summary. The possibility was examined of an association between umbilical cord whole blood viscosity and umbilical artery flow velocity time waveforms obtained with continuous wave Doppler ultrasound. The cord blood viscosity was measured at both high (100 s^-l) and low (0·1 s^-I) shear rates with a concentric cylinder viscometer. Plasma viscosity and fibrinogen were also measured. An abnormal pattern in the umbilical artery flow velocity waveform (high A/B ratio) indicative of high resistance was associated with an increase in whole blood viscosity at high shear (which may reflect a change in red cell rigidity). Viscosity at low shear (reflecting red cell aggregation and rouleaux formation) did not differ. There was a significant association between the small-for-gestational age fetus and abnormal umbilical artery waveform study ( P <0·002) but not abnormal whole blood viscosity at high ( P =0·09) or low ( P =0·08) shear.     

Doppler flow velocity waveforms and vasoactive effects of serotonin in human umbilical arteries

The vasoactive effect of serotonin was investigated by in vitro perfusion in human umbilical arteries in which antenatal Doppler ultrasound examination revealed abnormal velocity waveforms. The results were compared to those obtained in preparations from normotensive uncomplicated term pregnancies as well as from preterm deliveries in which antenatal Doppler ultrasound examination showed normal velocity waveforms related to gestational age. Serotonin induced a monophasic vasoconstriction or a biphasic pressure response with a transient pressure decrease succeeded by a constrictory response. In all groups serotonin induced a significant (p < 0.001) constrictory response, whereas no significant differences were observed between the groups. At a serotonin dose of 10(-7) mol/l, the frequency of preparations with a biphasic pressure response was significantly smaller in the preparations with abnormal diastolic flow as compared to the term control group (5/18 vs. 13/19, p = 0.02), but not significantly different from that of the preterm control group (3/9). The umbilical arterial responsiveness to serotonin does not seem to be dependent on antenatal Doppler velocity waveforms.     

Ultrasound study of blood flow velocity in the umbilical artery

The blood flow velocity waveforms fo the umbilical artery were examined in 101 healthy pregnant women in 146 occasions. A Kranzbühler 8130 Duplex Doppler equipment was used in all of the examinations. Their results were estimated by the A/B ratios (A = systolic peak, B = end diastole) and the Resistance Indexes (Formula: see text). It was found that the A/B ratio decreased from 3.0 to 2.0 and the Resistance Index from 0.6 to 0.5 from the 28th week of pregnancy till term. The changes showed that the resistance of the placental bed decreased continuously in healthy pregnant woman during the third trimester.     

Inferior vena cava diameter pulse waveforms in the human fetus: relationship with flow velocity waveform

Our purpose was to evaluate the hemodynamic significance of fetal inferior vena cava (IVC) flow velocity waveform indices during fetal development in relation to the diameter pulse waveform. Doppler ultrasound and a phase locked loop echo tracking system were used to measure flow velocity waveform and diameter pulse waveform, respectively. Twenty-seven normal singleton pregnancies were examined from 20 weeks until term at 4-week intervals. The diameter pulse waveform consisted of four waves (A, X, V, and Y waves). The A value (end-diastolic diameter) was associated with the end-diastolic pressure, which causes reverse flow during right atrial contraction. In normal fetuses, a weight-related lower end-diastolic diameter suggested that the end-diastolic pressure was decreased. Except for a positive correlation between the percent reverse flow during atrial contraction and the A value per unit fetal weight, no correlations were found between diameter waveform indices and blood flow velocity waveform indices. The peak velocity index of the velocity waveform significantly correlated with the umbilical artery flow velocity waveform systolic/diastolic ratio. The fetal IVC velocity waveform indices did not yield unequivocal information as to changes in central venous pressure, for which purpose the diameter pulse waveform analysis would seem to be the only available method.     

脐动脉波形异常伴胎儿宫内生长迟缓患者胎盘血管内皮生？…

目的 探讨胎儿脐动脉波形异常伴宫内生长迟缓（ＩＵＧＲ）与胎盘血管内皮生长因子（ＶＥＧＦ）表达水平的关系,并得出胎盘的氧水平。方法 应用彩色多谱勒超声,对４０例妊娠晚期妇女进行胎儿脐动脉搏动指数（ＰＩ）、阻力指数（ＲＩ）及收缩期末最大血流速度与舒张期末最小血流速度比值（Ｓ／Ｄ）测定,根据脐动脉波形变化分为４个组。脐动脉波形异常伴ＩＵＧＲ组（ＡＶＡＷ组）、脐动脉波形异常不伴ＩＵＧＲ组（ＡＶＮＷ组）、脐     

The effect of fetal heart rate on umbilical artery flow velocity waveforms

Umbilical artery flow velocity waveforms were obtained using continuous wave Doppler ultrasound in 85 normal pregnancies (25 antepartum, 60 intrapartum) to examine the relation between fetal heart rate, end systolic/end diastolic ratio (A/B ratio) and resistance index (RI). Our results demonstrated a significant negative correlation between fetal heart rate, A/B ratio and RI (in the antepartum group r = -0.49, and in the labouring group r = -0.65). It is therefore important when performing mathematical analysis of umbilical artery flow velocity profiles to make a statistical allowance for fetal heart rate.     

Normalisation of a severely abnormal ductus venosus Doppler flow velocity waveform in a growth-retarded fetus with absent end-diastolic flow in the umbilical artery and congenital anomalies

Doppler recordings of fetal venous blood flow seem to be superior to arterial velocimetry and CTG concerning the prediction of fetal outcome and optimal time of delivery in pregnancies with fetal growth retardation and AREDV. An improvement of arterial Doppler flow velocities has been described. We report the reappearance of a normal end-diastolic flow velocity in a ductus venosus temporarily showing reversed end-diastolic flow in a growth-retarded fetus with congenital anomalies. This normalization was accompanied by an improvement of the CTG, a loss of umbilical vein pulsations, a reappearance of umbilical diastolic flow and a progressive return of cerebral and venous blood flow into the 'normal' range. Improvement of fetal condition may be the explanation for our observation.