First-trimester uteroplacental and fetal blood flow velocity waveforms in normally developing fetuses: a longitudinal study.

Our objectives were to obtain a complete overview of uteroplacental and fetal hemodynamics early in pregnancy and to record flow velocity waveforms in the vitelline artery using color Doppler equipment. Flow velocity waveforms were recorded in 18 uneventful pregnancies between 6 and 16 weeks of gestation. Doppler recordings were made of the left and right uterine and spiral arteries from 6 weeks of gestation onwards. Recordings of c the umbilical artery, fetal aorta and fetal cerebral arteries started in weeks 7, 8 and 9, respectively. Where possible, the vitelline arteries were also recorded. The resistance and pulsatility indices and 95% confidence intervals for predictions were calculated.For the uterine and spiral arteries, characteristics of the waveforms were assessed. The resistance index of both uterine and spiral arteries gradually decreased with advancing pregnancy. For the umbilical artery, aorta and cerebral artery, the earliest possible Doppler recordings and characteristics of the waveforms were established. The pulsatility index of the umbilical arteries and fetal aorta showed a sharp decrease towards the 16th week. The pulsatility index of the fetal cerebral artery showed only a mild decrease towards week 16. In a longitudinal analysis, there were significant changes of the resistance and pulsatility indices for each patient. In the vitelline artery, recordings were possible in eight out of 18 fetuses, and only in weeks 7 and 8 of gestation. The pulsatility index showed a wide range and was not dependent on menstrual age.Knowledge of the normal flow velocity waveforms in the maternal uteroplacental and fetal circulations early in pregnancy may lead to a better understanding of physiological mechanisms.     

Hemodynamic factors affecting uterine artery Doppler waveform pulsatility in sheep.

Quantitative analysis of vascular resistance from the Doppler time-velocity waveform relies on measuring arterial pulsatility. However, input pressure waveform pulsatility, impedance, and resistance have all been found to effect artery flow waveform pulsatility in circulatory mathematic models and in umbilical sheep preparations in vivo. The present study used an in vivo sheep preparation to determine that embolization of the uteroplacental circulation and maternal angiotensin II administration caused changes in the uterine Doppler time-velocity waveform pulsatility that were dependent on input pressure waveform pulsatility, fundamental impedance, and resistance changes. Uteroplacental vascular embolization increased vascular resistance and the uterine artery Doppler waveform resistive index; the mean component of flow (mean pressure/resistance) decreased. Decreased uterine artery Doppler resistive index occurred despite angiotensin II-induced vasoconstriction and increased vascular resistance because the pulse component of flow (pulse pressure/impedance) decreased.     

The impact of maternal plasma volume expansion and antihypertensive treatment with intravenous dihydralazine on fetal and maternal hemodynamics during pre-eclampsia: a clinical, echo-Doppler and viscometric study.

OBJECTIVES: To establish the effects of plasma volume expansion (PVE) followed by intravenous dihydralazine (DH) administration on maternal whole blood viscosity (WBV) and hematocrit, uteroplacental and fetoplacental downstream impedance and umbilical venous (UV) volume flow in pre-eclampsia. METHODS: In 13 pre-eclamptic women maternal and fetal hemodynamics were established by means of combined measurement of maternal arterial blood pressure (BP), WBV, hematocrit and uterine artery (UtA) resistance index (RI) in addition to umbilical artery (UA) pulsatility index (PI) and UV volume flow obtained from UV vessel area and UV time-averaged flow velocity. In each woman all parameters were measured four times at baseline, after PVE, after DH and 24 h after the start of treatment. RESULTS: Maternal diastolic BP, hematocrit and WBV display a significant reduction after PVE. In the fetus UA PI decreases significantly whereas a significant increase in UV cross-sectional area was detected. After maternal DH administration, arterial systolic and diastolic BP and UA PI show a significant decrease compared with the measurements following PVE. At 24 h, only maternal systolic and diastolic BP display a significant further decrease. No significant changes were established for the UtA RI, UV time-averaged velocity and UV volume flow during the entire study period. CONCLUSIONS: During pre-eclampsia, maternal PVE followed by DH administration results in a significant reduction in maternal diastolic BP, maternal hematocrit and WBV. Maternal PVE is associated with a significant increase in UV cross-sectional area and a non-significant rise of 11% in UV volume flow. Maternal DH administration does not result in any change in UV cross-sectional area. However, UA PI decreases significantly after both PVE and DH treatment.     

Effects of maternal hyperoxia with and without normocapnia in uteroplacental and fetal Doppler studies.

OBJECTIVE: One hundred percent oxygen is given in pregnancy to improve fetal oxygenation, yet has been shown in both animal and human studies ex utero to increase cerebral vascular resistance. Adjusting end-tidal pCO2 (ET-pCO2) levels to normocapnic levels during hyperoxygenation offsets this effect in non-pregnant individuals. We aimed to evaluate the effect of maternal hyperoxygenation with and without maintaining normocapnia on the fetal and uteroplacental circulations in healthy near-term human pregnancies. METHODS: Eight healthy pregnant women, serving as their own controls, sequentially breathed room air, breathed 100% oxygen, and underwent normocapnic hyperoxygenation (NH) in a three-phase experiment involving a tight-fitting facemask. Each phase lasted 10-15 min. After steady state had been reached, peak velocities and pulsatility index (PI) values were obtained from the uterine, umbilical and fetal middle cerebral arteries (MCA) by color/pulsed Doppler. In addition, maternal ventilation and ET-pCO2 were monitored. RESULTS: One hundred percent oxygen induced maternal hyperventilation and hypocapnea. Uterine artery PI and peak systolic velocities were stable during 100% oxygen. In contrast, during NH uterine artery PI values decreased by 21% (P=0.04). Umbilical artery PI and peak velocities were stable during 100% oxygen; PI increased by 16% during NH (P=0.056), with no change in peak velocities. Peak MCA velocities decreased by 8% during 100% oxygen, and by 9.6% during NH, while MCA-PI decreased by 13% during 100% oxygen and by 21% during NH (P=0.06). CONCLUSIONS: Maternal and fetal circulations exhibit divergent responses to 100% oxygen and NH. While no change is observed in the uteroplacental circulation on 100% oxygen, decreased resistance and increased flow velocity are evident during NH. Increased umbilical artery PI during NH with no change in absolute velocities may suggest a reduction in fetoplacental blood flow. Maintaining normocapnia during hyperoxygenation does not appear to beneficially influence the circulation of the near-term human fetus as it does in non-pregnant individuals.     

Chronic glomerulonephritis and pregnancy

AIM: To clarify factors of risk for unfavourable variants of gestational chronic glomerulonephritis (CGN) and poor pregnancy outcomes in CGN; to determine prognostic implications of changes in some renal and uteroplacental indices. MATERIAL AND METHODS: Variants of CGN gestational course and pregnancy outcomes have been analysed for 156 CGN patients. The women were examined before pregnancy, in the course of pregnancy and 3-24 months after the delivery. Measurements were made of 24 h proteinuria, glomerular filtration rate, blood transaminases activity, functional renal reserve (FRR), uricemia, blood level of alpha-phetoprotein. Placentas were studied morphologically, uterine and umbilical artery circulation was assessed by dopplerometry. RESULTS: The following abnormalities were registered: high proteinuria (34.6%), progression of hypertension (29.5%), renal function deterioration (15.4%), fetal and neonatal losses (15.4%), fetal underdevelopment (25%), preterm delivery (17.3%), preeclampsia (7.7%), preterm placental detachment (1.9%). There is morphological, dopplerometric and biochemical evidence for placental insufficiency in CGN pregnant women. CONCLUSION: Activity of CGN (nephritic or acute nephritic syndromes), hypertension, renal failure, disorders of renal hemodynamics are factors of risk for unfavourable gestational course of CGN and pregnancy complications. Placental insufficiency deteriorates pregnancy outcomes in CGN, but changes in uterine and umbilical circulation as well as blood levels of alpha-fetoprotein are not prognostically significant.     

正常早孕子宫血流变化的多普勒超声检测

本文对６８例不同时期早孕妇女子宫动脉和子宫螺旋动脉多普勒超声检测结果作了比较分析。结果显示：子宫动脉血流阻力无明显变化，子宫螺旋动脉血流阻力逐步降低；结合子宫的血供特点加以探讨，认为子宫螺旋动脉的阻力指数（ＲＩ值）能敏感地反映早孕的血流动力学变化，可精确估价早期妊娠子宫胎盘的血流循环。     

Effect of maternal posture on the umbilical artery flow velocity waveform.

The effect of maternal postural changes on the umbilical artery flow velocity waveform, fetal heart rate and maternal blood pressure was studied in 27 normal singleton pregnancies between 23 and 36 weeks of gestation. A statistically significant change in umbilical artery Pulsatility Index (PI) was established for both maternal standing to supine position (rise) and supine to standing position (drop). These PI changes were not related to gestational age. A statistically significant drop in maternal systolic blood pressure was observed from standing to supine position. The rise in umbilical PI resistance when changing from standing to supine position may be caused by the sluice flow mechanism.     

Fetal and uteroplacental blood flow in prolonged pregnancies. A clinical study.

In a prospective study during 1 year, 102 women with prolonged pregnancies (more than 294 completed gestational days) were followed with serial pulsed Doppler blood flow examinations every 2nd day, either to spontaneous onset of labor (n = 82) or to induction of labor due to subsequently occurring complications (n = 20). Mean aortic blood velocity did not change significantly with gestational age beyond 294 days either in fetuses with normal outcome or in fetuses that developed asphyxia at birth. The flow velocity waveforms in the descending aorta, the umbilical artery, the common carotid artery and the uterine artery did not change significantly compared to the values at term. Abnormal flow velocity waveforms in the fetal descending aorta, umbilical artery or uterine artery had no significant relationship to fetal asphyxia. Absence of diastolic flow velocities was not found in any of the vessels examined, indicating that the fetuses did not suffer from chronic hypoxia in utero and that aging of the placenta did not alter fetal and uteroplacental blood flow. Notching of the aortic flow velocity waveform was a common finding among prolonged pregnancies. The hemodynamic implications and consequences of this phenomenon are discussed.     

Second trimester Doppler ultrasound screening of the uterine arteries differentiates between subsequent normal and poor outcomes of hypertensive pregnancy: two different pathophysiological entities?

The 'classical' concept that pregnancy-induced hypertension (PIH) and pre-eclampsia (PE) primarily originate from defective placentation in early pregnancy has been challenged recently. There is growing evidence that other factors, including maternal predisposing conditions, also play a significant role in the pathophysiology of PIH and PE. The aim of the present study was to test the hypothesis that PIH and PE with an early onset and poor pregnancy outcome is associated with defective placentation, e.g. inadequate spiral artery dilatation and subsequent reduced uteroplacental perfusion, whereas PIH and PE with normal pregnancy outcome is not. Using Doppler ultrasound, we measured the uterine artery pulsatility index (PI) in a population of 531 nulliparous women in the 22nd week of gestation. Uterine artery PI was used as an index of resistance to blood flow in the uteroplacental circulation. Outcome measures were PIH/PE with or without poor pregnancy outcome, preterm birth and intra-uterine growth restriction (IUGR). The results revealed a striking difference between PI values for PIH/PE with and without poor pregnancy outcome. Uterine artery PI in the 22nd week was increased significantly in pregnancies which developed early-onset (before 35 weeks) PIH/PE with a poor pregnancy outcome. In contrast, uterine artery PI values were normal in women who developed PIH/PE, but had a good pregnancy outcome. There was a significant correlation between 22nd week uterine artery PI and subsequent preterm birth or IUGR. Our results indicate that only PIH/PE with poor pregnancy outcome is associated with defective placentation, whereas PIH/PE with good outcome is not. These findings support the concept of heterogeneous causes of hypertensive disorders of pregnancy.     

Role of adenosine in regulation of uterine blood flow during nonpreeclamptic twin gestation

We evaluated the possible role of increased adenosine in the regulation of uteroplacental circulation during nonpreeclamptic twin gestations. We performed uterine artery Doppler velocimetry and maternal arterial blood sampling for measurement of plasma adenosine levels in 16 women with singleton gestation and 14 women with dichorionic twin gestation without preeclampsia at 11-12, 25-26 and 34-36 weeks. In singleton gestations, a negative correlation between maternal plasma adenosine levels and maternal uterine artery pulsatility index was observed. In twin gestations, there were no noticeable association between maternal plasma adenosine levels and maternal uterine artery pulsatility index. Our results suggest that the decrease in vascular resistance in twin gestations may be through the mechanisms that are independent of adenosine.     

剪切波技术对先兆子痫患者胎盘弹性的初步研究

目的：探讨剪切波弹性成像（shear wave elastography,SWE）技术定量分析先兆子痫患者胎盘弹性的临床应用价值。 方法：选取单胎妊娠妇女76例（先兆子痫组22例，健康对照组54例），常规测量脐动脉、双侧子宫动脉血流动力学参数（S/D、PI、RI），SWE测量胎盘中央胎儿面、中央母体面、边缘胎儿面、边缘母体面四个不同区域弹性模量值。根据胎盘四个区域平均弹性模量值绘制ROC曲线，获取诊断先兆子痫的最佳临界值，计算敏感性、特异性、阳性预测值、阴性预测值。 结果：先兆子痫组胎盘中央胎儿面、中央母体面、边缘胎儿面、边缘母体面弹性模量值分别为：8.54±3.74KPa、9.46±3.64KPa、8.48±2.66KPa、9.25±3.00KPa，健康对照组弹性模量值分别为：6.38±1.87KPa、6.51±1.52KPa、6.37±1.55KPa、6.48±1.58KPa，先兆子痫组四个区域弹性模量值均高于健康对照组，差异有统计学意义（P＜0.05）。两组资料胎盘四个区域之间弹性模量值差异无统计学意义（P＞0.05）。胎盘弹性模量平均值预测先兆子痫的ROC曲线下面积为0.754，界值为8.19KPa，敏感性、特异性、阳性预测值、阴性预测值分别为64%、96%、88%、87%，符合率87%。胎盘弹性模量值与双侧子宫动脉血流动力学参数低度相关（P＜0.05），与脐动脉血流动力学参数无显著相关性（P＞0.05）。 结论：先兆子痫孕妇胎盘硬度较正常孕妇高，SWE技术可以定量获得胎盘组织硬度，有助于评估先兆子痫孕妇胎盘功能。     

Doppler studies of the uteroplacental circulation in pregnancies complicated by diabetes.

The aim of this study was to evaluate the uteroplacental side of the circulation in pregnancies complicated by diabetes. A total of 54 women with pregnancies complicated by diabetes underwent uterine and umbilical artery Doppler studies. Uterine Doppler velocity waveforms were not obtained in two women. The prevalence of abnormal uterine artery velocity waveforms was much higher than in a non-diabetic population (15.4% vs. 2%, p < 0.001). Those eight women with abnormal uterine Doppler studies had a statistically higher incidence of poor glycemic control, chronic hypertension, polyhydramnios, vasculopathy, pre-eclampsia, Cesarean births for fetal distress and newborns with respiratory distress syndrome. In this group of patients, the umbilical circulation was not considered to be a contributing factor in the development of problems.     

Nifedipine therapy for preterm labor: effects on placental, fetal cerebral and atrioventricular Doppler parameters in the first 48 hours.

OBJECTIVE: To assess the effect of nifedipine tocolysis on Doppler parameters of the uterine, umbilical and fetal middle cerebral arteries and atrioventricular valves in the first 48 h of therapy. METHODS: Doppler waveforms of uterine, umbilical and middle cerebral arteries and both atrioventricular valves were measured from 28 pregnant women and fetuses prior to and during nifedipine therapy for preterm labor. Maternal and fetal heart rates (FHR), maternal systolic and diastolic blood pressure, and the Doppler pulsatility index (PI) of the uterine, umbilical and middle cerebral arteries were measured. The cerebroplacental ratio (middle cerebral artery PI/umbilical artery PI) was calculated. The total time velocity integrals (TVIs) of tricuspid and mitral valves and their E- and A-wave peak velocity ratio (E/A) were measured. Friedman repeated-measures analysis of variance was used to compare the variables before and after nifedipine therapy. If significant differences were found, Wilcoxon's signed ranks test was used to analyze the difference between the two variables. A P-value of < 0.05 was considered significant. RESULTS: Nifedipine maintenance was associated with a significant decline in maternal systolic and diastolic blood pressure after 24 h, while maternal heart rate and FHR were unaffected. The uterine artery PI had decreased significantly at 24 and 48 h, while the umbilical artery PI did not change significantly. The middle cerebral artery PI had decreased significantly at 24 and again at 48 h. A significant fall in the cerebroplacental Doppler ratio was maintained beyond 24 h. The mean E/A values, TVIs and TVI x FHR values at 24 and 48 h were unchanged from the baseline values. CONCLUSIONS: Nifedipine maintenance tocolysis is associated with a significant decline in uterine artery and middle cerebral artery Doppler indices 24 h after the first dose. Fetal cardiac diastolic function is unaffected and the significant redistribution observed after 24 h is likely to be attributable to altered cerebral blood flow.     

Impaired uteroplacental blood flow in pregnancies complicated by falciparum malaria.

OBJECTIVE: In endemic areas, maternal malaria infection is usually asymptomatic. However, it is known that infected maternal erythrocytes sequester in the intervillous space of the placenta. There is a strong association between placental malaria infection and both low birth weight (LBW) and severe maternal anemia. We aimed to determine whether impaired uteroplacental blood flow might account for the low infant birth weight associated with maternal falciparum malaria infection. METHODS: This observational study was carried out during a large double-blind, randomized, controlled trial of an antimalarial drug intervention for primigravidae. Nine hundred and ninety-five women were recruited from the antenatal clinic at a district hospital on the Kenya coast and had at least one Doppler ultrasound scan. Uterine artery resistance index and the presence or absence of a diastolic notch were recorded. In the third trimester, blood was taken for hemoglobin and malaria film. RESULTS: Malaria infection at 32-35 weeks of gestation was associated with abnormal uterine artery flow velocity waveforms on the day of blood testing (relative risk (RR) 2.11, 95% confidence interval (CI) 1.24-3.59, P = 0.006). This association persisted after controlling for pre-eclampsia. Impaired uteroplacental blood flow in the women studied was also predictive of poor perinatal outcome, including low birth weight, preterm delivery and perinatal death. The risk of preterm delivery in women with histological evidence of past placental malaria infection was more than twice that of women without infection (RR 2.33, 95% CI 1.31-4.13, P = 0.004). CONCLUSIONS: Uteroplacental hemodynamics are altered in the presence of maternal falciparum malaria infection. This may account for some of the excess of LBW babies observed in malaria endemic areas. Strategies that prevent or clear placental malaria may confer perinatal benefit through preservation of placental function.     

Effects of low-dose aspirin on uterine and fetal blood flow during pregnancy: results of a randomized, placebo-controlled, double-blind trial.

OBJECTIVE: This study was conducted to evaluate uteroplacental and fetal hemodynamics in fetuses exposed to low-dose aspirin (100 mg/d). DESIGN: Randomized, placebo-controlled, double-blind trial. SUBJECTS: The study protocol included singleton pregnancies of less than 20 gestational weeks at risk for pre-eclampsia or fetal growth restriction. Exclusion criteria were diabetes mellitus, pre-existing proteinuric hypertension or fetal malformations. Forty-three pregnant women were randomly allocated to daily treatment with 100 mg aspirin (n = 22) or placebo (n = 21). METHODS: Pulsed Doppler measurements of the uterine artery, fetal middle cerebral artery, fetal aorta, ductus arteriosus and atrioventricular valves were performed longitudinally at 14 day intervals starting from 18 gestational weeks until delivery. Results were expressed as group medians (aspirin vs. placebo) and were analyzed by Mann-Whitney U-test. RESULTS: There was no difference in uterine, umbilical, aortic, middle cerebral and ductus arteriosus blood flow between the aspirin group and controls. Median ductal peak flow velocities increased with gestational age in both groups, but differences between groups did not reach significance. In the third trimester of pregnancy, ductal peak velocities > 140 cm/s were occasionally observed in both groups. However, end diastolic velocities > 35 cm/s or atrioventricular valve regurgitation never occurred. CONCLUSIONS: Daily administration of low-dose aspirin during the second and third trimesters of pregnancy does not alter uteroplacental or fetoplacental hemodynamics and does not cause moderate or severe constriction of the ductus arteriosus.     

子痫前期患者子宫动脉多普勒与血清chemerin的变化及意义

目的:讨论妊娠期高血压孕妇和正常妊娠妇女妊娠早、中、晚期子宫动脉血流变化及血清chemerin变化的规律及意义。方法:选取潍坊市妇幼保健院系统产前检查的孕妇共300例作为研究对象,分别于妊娠14周、24周、34周收集和测量两组孕妇的血液样本和子宫动脉多普勒信息。比较两组孕妇血清chemerin浓度,子宫动脉舒张末期流速(S/D)、搏动指数(PI)、阻力指数(RI)。结果:1)子痫前期患者血清中chemerin浓度明显高于对照组(P<0.05),且重度子痫前期组明显高于轻度子痫前期组(P<0.05)。2)子宫动脉血流动态变化:正常妊娠组孕妇随妊娠进展,子宫动脉RI、PI、S/D 3项指标逐渐降低,妊娠早、中、晚期分别比较,均有统计学差异(P<0.01)。子痫前期组孕妇子宫动脉RI、PI、S/D 3项指标以孕晚期最高,妊娠早、中、晚期分别比较,均有统计学差异(P<0.01)。子痫前期组孕妇妊娠中、晚期子宫动脉3项指标均高于正常妊娠组,有统计学差异(P<0.01)。3)子痫前期患者血清中chemerin浓度在孕早期与子宫动脉血流无明显相关性,在妊娠中晚期呈明显正相关。结论:随着妊娠进展,子痫前期患者血清中chemerin浓度逐渐升高,正常妊娠妇女子宫动脉的血流阻力逐渐下降;而子痫前期组孕妇随妊娠进展子宫动脉的血流阻力明显升高。两者共同参与妊娠期高血压的发病。     

Effect of placental resistance, arterial diameter, and blood pressure on the uterine arterial velocity waveform: a computer modeling approach

A computer model was used to simulate velocity waveforms that can be visualized in the human uterine artery using Doppler ultrasound. It was found that increasing uteroplacental vascular resistance from normal caused an increase in the systolic/diastolic velocity ratio (S/D) and pulsatility index (PI) of the waveform. Increasing uteroplacental resistance also caused the appearance of a dicrotic notch. Reducing the uterine artery radius increased the S/D and PI and this effect was accentuated at high placental resistance. In contrast, increasing mean arterial pressure in the uterine artery had little effect on S/D and PI. Results suggest that waveform shape abnormalities observed in obstetric patients with pregnancy-induced hypertension are primarily caused by high uteroplacental vascular resistance and a reduced uterine arterial diameter.     

Maternal uterine artery Doppler studies at high altitude and sea level.

OBJECTIVE: To determine uterine artery impedance using Doppler in the second and third trimesters at sea level and at high altitude. METHODS: Uterine artery resistance and pulsatility indices (RI and PI, respectively) were obtained by Doppler velocimetry from 242 women in Cerro de Pasco (4300 m altitude) and 200 women in Lima (sea level), all with normal singleton pregnancies between 14 and 40 weeks of gestation. Impedance indices at high altitude and sea level were compared using fractional polynomial regression analysis. RESULTS: Impedance to uterine artery blood flow was lower at high altitude than at sea level (for PI ratio Lima/Cerro de Pasco = 1.06; P = 0.011). If gestation bands were compared, the difference was significant up to 25 weeks. CONCLUSION: At high altitude, pregnancy is associated with lower uteroplacental impedance than at sea level. This may reflect a compensatory mechanism of uteroplacental development to lower oxygen tension associated with altitude.     

Central arterial hemodynamics in small-for-gestational-age fetuses before and during maternal hyperoxygenation: a Doppler velocimetric study with particular attention to the aortic isthmus.

OBJECTIVE: Hemodynamic changes indicating a normalization of fetal blood flow redistribution during maternal oxygen administration have been suggested to be of positive prognostic value in growth-restricted fetuses. The aortic isthmus has been suggested as a site for early detection of blood flow redistribution as well as for verification of a response to maternal hyperoxygenation. The present study was performed to investigate whether this concept could be confirmed in a study involving fetuses assumed to have only a moderate disturbance in fetoplacental hemodynamics. DESIGN AND SUBJECTS: Twenty-five singleton fetuses with an estimated weight less than -2 SD below the gestational age-related mean and without any malformation or chromosomal aberration were studied between 27 and 38 (median 34) weeks of gestation. METHODS: Velocity waveforms from the mitral valve, aortic valve, middle cerebral artery, aortic isthmus and umbilical artery were recorded before and during maternal breathing of 100% oxygen. RESULTS: Nine fetuses demonstrated absent or reversed end-diastolic velocity (ARED) in the aortic isthmus while forward flow was present in the umbilical artery. The cerebral artery pulsatility index (PI) increased with oxygen administration and there was a decrease in the aortic isthmus PI. Variables obtained from the other recording sites did not change with maternal hyperoxygenation. CONCLUSIONS: ARED in the aortic isthmus appears to be an early sign of blood flow redistribution in this group of fetuses. Maternal oxygenation results in velocity waveform changes that suggest an increase of cerebral vascular resistance and a redistribution of blood from the brain to the vascular beds supplied by the descending aorta. The aortic isthmus is a suitable site to verify this response.     

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.