Doppler velocimetry of intraplacental fetal arteries

Doppler velocimetry of the umbilical and intraplacental fetal arteries was studied by color flow mapping in 39 normal pregnancies. The systolic-diastolic ratio (S/D) and pulsatility index of the intraplacental fetal artery downstream to the umbilical artery decreased significantly with advancing gestational age, and its S/Ds were persistently lower than those of the umbilical artery. The difference in the S/D between the umbilical artery and its intraplacental downstream branches decreased with advancing gestational age and approached zero as the pregnancy progressed to term. We conclude that intraplacental fetal arteries, possibly fetal arteries in main stem villi, can be imaged by color flow mapping and that there is a significant "resistance gradient" between the intraplacental fetal artery and the umbilical artery. Intraplacental fetal artery velocimetry using color flow mapping may give further insights into the umbilical-placental circulation.     

Prognostic Doppler ultrasound examination of fetal arteries blood flow

Early detection of fetal risk is one of the main issues in today obstetrics. Ultrasound diagnostics plays a significant role, as the introduction of Doppler imaging method in the evaluation of blood flow has enabled non-invasive assessment of uteroplacental circulation. Therefore, we have analysed foetal three arteries: umbilical artery, middle cerebral artery and renal artery after determining the normal range for the analysed parameters. AIM OF WORK: 1. Comparison of the obtained blood flow indices (S/D, RI, PI) in the umbilical artery, middle cerebral artery and renal artery of foetuses from normal and complicated full-term pregnancies. 2. Determination of indices: umbilical-cerebral and renal-cerebral in normal and pathological pregnancy. 3. Evaluation of feasibility of the analysed flow parameters for the detection of intrauterine foetal hypoxia. MATERIAL AND METHODS: We have examined 151 women, who were divided into control group--101 pregnant women with normal pregnancy and study group--50 pregnant women with complicated pregnancy. All pregnant women underwent ultrasound examination using the Hitachi EUB 515 C (Japan) scanner with 3.5 MHz convex probe, connected to the colour pulsed Doppler. The study consisted of the biometric measurements and evaluation of the spectrum of blood flow in the umbilical artery, middle cerebral artery and renal artery. We have determined following indices: a) systolic-diastolic ratio S/D, resistance index RI, pulsatility index PI, b) umbilical-cerebral ratio P/M. (PI ua/PI mca), renal--cerebral ratio N/M (PI ra/PI mca). RESULTS: Statistically significant difference was found between the study and control groups for all the flow indices assessed (S/D, RI, PI) for the middle cerebral artery, for the indices P/M and N/M. (p < 0.001) and pulsatility index in the renal artery (p < 0.01). Similar, although slightly smaller difference (p < 0.05) was seen for the values of flow parameters in the umbilical artery. CONCLUSIONS: 1) Evaluation of blood flow in the middle cerebral artery, and in particular pulsatility index PI, reflects the risk to foetus. Umbilical-cerebral index and renal-cerebral index demonstrate the mechanisms of circulation centralization in case of fetal distress. For the umbilical-cerebral index, the cut-off value is 1.0 and for the renal-cerebral index it is 2.5, 2) Evaluation of the blood flow in foetal vessels is a significant element of prenatal diagnostics. Due to its low sensitivity, it should be compared with the results of other biophysical tests, to achieve complex evaluation of the condition of the foetus.     

Clinical assessment of fetal blood flow velocimetry.

A statistical procedure is presented to analyze the relation between Doppler indices (DIs) such as pulsatility index (PI), resistance index (RI), A/B and clinical data of pregnancy and fetal outcome of three groups: (1) uncomplicated pregnancy, eutrophic fetus (NF), (2) pregnancy-induced hypertension (PIH), and (3) pregnancy and delivery of a dystrophic fetus (IUGR), and the acidity classes according to Saling, respectively. Proceeding and mathematical requirements as well as the possibilities to validate the methodology are introduced, and an application to previously published data is presented. By multivariate analysis of the data a fair prognosis of NF, PIH and IUGR was possible. The variability inherent to the data sampling requires a mathematical postprocessing in the framework of an adequate model before any clinical conclusions can be derived from DIs.     

Integrated monitoring of fetal growth restriction by computerized cardiotocography and Doppler flow velocimetry

OBJECTIVE: To investigate the correlations between Doppler flow velocimetry and computerized cardiotocography (cCTG) in fetal growth restriction. STUDY DESIGN: Fifty growth-restricted foetuses with abdominal circumference below the 10th percentile and no major abnormalities were studied. A total of 186 cCTG tracings (at least two per patient) analysed using the HP2CTG system were compared with the corresponding umbilical artery pulsatility index (PI), the PI ratio of umbilical artery to middle cerebral artery, and the ductus venosus systolic/atrial ratio. RESULTS: Worsening in umbilical artery Doppler velocimetry parameters was associated with a significant reduction of short- and long-term variability indices and accelerations. When end-diastolic umbilical artery flow was preserved, a reversed ratio between umbilical artery and middle cerebral artery PIs was not correlated with a worsening of cCTG parameters; in the presence of umbilical artery absent or reversed flow, ductus venosus Doppler velocimetry abnormalities were correlated with a significant reduction of variability. When end-diastolic umbilical artery flow was preserved, there was a progressive increase in variability indices and accelerations with advancing gestational age. In the more compromised fetuses this "maturation" process of cCTG patterns was not found. CONCLUSION: There is a strict correlation between Doppler velocimetry abnormalities and cCTG parameter deterioration, in particular between ductus venosus and variability.     

Evaluation of fetal right coronary artery blood flow velocimetry

OBJECTIVES: In the present study fetal right coronary artery blood flow velocimetry was assessed. DESIGN: The prognostic value of the fetal right coronary artery blood flow velocimetry was evaluated in relationship with parameters of newborn's condition after birth. MATERIAL AND METHODS: The study was performed in 102 cases of pregnancies complicated by pregnancy induced hypertension. Blood flow velocimetry was visualized from fetal right coronary artery and correlated with perinatal outcome parameters. RESULTS: Fetal coronary blood flow velocimetry was visualized only in 11 cases. Coronary blood flow velocimetry visualisation correlated with each parameter of after-birth evaluation. The method has the highest specificity (97.7%) and positive prognostic value (85%) concerning evaluation of newborn's condition. CONCLUSIONS: Fetal right coronary artery blood flow velocimetry visualisation is a late sign of chronic fetal hypoxia. This seems to be a factor which causes maximal coronary vessels dilatation and allows oxygenation of fetal heart muscle.     

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.     

Qualitative assessment of maternal uterine and fetal umbilical artery blood flow and resistance in laboring patients by Doppler velocimetry

The purpose of this study is to evaluate the effect of uterine contractions during labor on both the uterine and the umbilical circulations. Twenty-seven patients in active labor were studied by continuous-wave Doppler velocimetry. Umbilical, left uterine, and right uterine arterial waveforms were obtained before, during, and after peak uterine contractions, and the ratio of maximum systolic and minimum diastolic velocities was calculated. Fifteen patients showed absent flow in end diastole on the uterine artery waveform and had significantly higher intra-amniotic pressures (64.5 +/- 3.5 mm Hg) during the peak amplitude of the uterine contraction compared with the 12 patients with maintained end diastolic flow (46.5 +/- 2.6 mm Hg; p less than 0.05). During the peak amplitude of the uterine contractions the 12 patients maintaining end-diastolic flow had significantly higher systolic/diastolic ratios in the uterine artery (6.5 +/- 1.5) compared with either before or after a contraction (2.1 +/- 0.15 and 2.0 +/- 0.2, respectively; p less than 0.05). Also, these 12 patients showed a linear relationship between the systolic/diastolic ratio and the intrauterine pressure. However, no differences were observed in the umbilical artery systolic/diastolic ratios before, during, or after a contraction in the intensity range studied. On the contrary, during contractions an increase in uterine artery resistance occurs with decreased or absent end-diastolic flow, which bears an inverse linear relationship to the intensity of the contraction. This suggests that during uterine contractions the human fetus continues to have uninterrupted fetoplacental blood flow, whereas the degree of interruption or reduction in uteroplacental blood flow is dependent on the intensity of uterine contraction.     

Hemodynamic changes in the fetal arteries during the second half of pregnancy assessed by Doppler velocimetry

The applicability of Doppler velocimetry has been well established regarding intrauterine growth restriction and fetal hypoxia. This method can also be used to determine fetal anemia and cardiac malformations. The main fetal arteries evaluated by Doppler velocimetry are the middle cerebral artery and the umbilical artery. However, the fetal aorta is responsible for the distribution of blood flow to the upper and lower extremities of the human body and should also be properly valued. In order to characterize abnormalities in the arteries of high-risk fetuses, it is necessary to know the hemodynamic modifications of normal fetuses. On this basis, the authors performed a review of fetal hemodynamics evaluated by Doppler velocimetry in the fetal aorta and middle cerebral and umbilical arteries during the second half of pregnancy. The study of fetal vessels by Doppler velocimetry indirectly evaluates the hemodynamic changes occurring in fetuses at risk. In this respect, we emphasize the changes in Doppler velocimetry occurring in fetal anemia, in restricted intrauterine growth, and in normal fetuses.     

The role of Doppler blood flow velocimetry in multiple pregnancy

This article focuses on Doppler velocimetry in the assessment of fetal growth, placental insufficiency, management of intrauterine growth restriction, discordant growth and twin-twin transfusion syndrome. Problems specific to multiple pregnancy such as twin reversed arterial perfusion, cord entanglement and visualization of anastomoses are also reviewed. Doppler sonography seems to be superior to other tests for early detection of placental insufficiency during surveillance of multiple pregnancies. It is suggested that Doppler sonography helps to select multiple fetuses who are at higher than normal risk, and might reduce perinatal mortality and morbidity. Fetal echocardiography may provide an accurate assessment of cardiovascular adaptation to intertwin transfusion, early recognition of deterioration and evaluation of antenatal management. In the management of the twin-twin transfusion syndrome, Doppler echocardiography and Doppler ultrasound examination of the venous circulation appear to be useful tools for improved perinatal management. Doppler sonography is an important adjunct in monitoring high-risk multiple pregnancies.     

The assessment of fetal well-being by venous Doppler velocimetry

The assessment of fetal well-being by venous Doppler velocimetry, especially in cases of intrauterine growth restriction, has been growing in importance as a number of researchers have been improving their studies^1 - 5 as well as a consequence of better technologies in ultrasound equipment. Since different authors have studied the fetal blood circulation with color Doppler, initially focusing their attention on the arterial system^6 - 12, many questions and doubts have remained without a reasonable answer, especially concerning the optimal time at which to deliver these fetuses. Among these authors, some have expressed the opinion that all biophysical methods, including the cardiotocogram, should be used before the decision of fetus delivery should be made^13,14. It is possible, nowadays, to study several venous vessels, such as the ductus venosus, inferior vena cava, umbilical vein, portal vein, hepatic veins¹⁵, and, more recently^1,2, the cerebral transverse sinus. The purpose of this review is to describe the fetal circulation, the technique and rationale behind measuring venous Dopplers and to assess the clinical applications of venous Doppler velocimetry.     

Prenatal prediction of lethal pulmonary hypoplasia using ultrasonic fetal chest circumference

Ultrasonic measurement of fetal chest circumference was tested as a predictor of pulmonary hypoplasia in a group of 26 fetuses at known risk. A 42% prevalence of autopsy-proved pulmonary hypoplasia was found in this population. Chest circumference measurements were plotted on published nomograms based upon head circumference, femur length, and gestational age. Longitudinal observations revealed a progressive lag in chest circumference growth among fetuses who proved to have pulmonary hypoplasia. The nomogram based on femur length provided sensitivity, specificity, and normal and abnormal predictive values of 80, 92, 92, and 89%, respectively. The results of this investigation suggest that fetal chest circumference measurement is a useful adjunct in establishing the diagnosis of lethal pulmonary hypoplasia.     

The current status of maternal and fetal blood flow velocimetry

Significant progress has been achieved in regard to normative data for uteroplacental and fetal blood flow velocity and the factors which may affect these observations. Associations have been demonstrated between abnormal indices of maternal and fetal blood flow velocity and pregnancy-induced hypertension, fetal growth retardation, fetal blood gas measures, and intrapartum clinical fetal distress. However, in general, the predictive power is modest and no evidence has yet been provided to indicate that these measures can be used as a screening test in the general obstetric population. Continuing research is highly desirable. At the present time, the use of Doppler assessment of blood flow in pregnancy should be limited to the investigational setting.     

Ultrasonic ratio of fetal thoracic to abdominal circumference: an association with fetal pulmonary hypoplasia

Real time ultrasound was used in pregnant women who were considered to be at risk for development of pulmonary hypoplasia (n = 26). The population consisted of women who had either premature rupture of membranes (n = 16) or oligohydramnios (n = 10). The ratio calculated by comparing the fetal thoracic circumference to abdominal circumference was obtained in all cases within 10 days of delivery. This ratio correlated strongly with neonatal outcome. Multivariate regression models of neonatal outcome were developed to analyze the relationship of gestational age at which premature membrane rupture occurred, the duration of premature rupture, date of birth, and prenatal diagnosis. The addition of the thoracic circumference to the abdominal circumference ratio increased significantly the proportion of explained variability. Application of this ratio should be considered in evaluating fetal status in oligohydramnios and in the expectant management of premature rupture of membranes.     

Placental morphometry and Doppler flow velocimetry in cases of chronic human fetal hypoxia

OBJECTIVE: To investigate the structural basis of abnormal Doppler waveforms in the utero-placental circulations in cases of chronic fetal hypoxia. STUDY DESIGN: Morphometric analysis was performed on placental samples from 58 pregnancies with abnormal Doppler waveforms in the uterine, placental and umbilical circulations at 32-34 weeks, and 10 pregnancies with normal waveforms. RESULTS: The volume of placental villi reduced from 350.5 cm3 in controls to 286.4 cm3 (P<0.05) in the severest cases. The volume of the fetal capillaries reduced from 59.7 cm3 to 20.5 cm3 (P<0.05). These reductions were associated with increased placental infarction. The myometrial segments of the spiral arteries were severely constricted, demonstrating failure of physiological conversion secondary to deficient trophoblast invasion. CONCLUSION: The placental vascular bed is greatly reduced in cases of chronic fetal hypoxia. We propose impaired placental perfusion causes oxidative stress and regression of the fetal vasculature, leading to fetal growth retardation and distress.     

Doppler measurements of maternal and fetal blood flow

Data accumulated over the last decade suggest that Doppler flow velocity waveforms can be used to study both maternal and fetal circulation. Information obtained with this technique appears useful as a screen for both maternal and fetal risk, as an aid to understanding perinatal anatomy and physiology, and as an adjunct to standard means of fetal surveillance.     

Doppler velocimetry determined redistribution of fetal blood flow: Correlation with growth restriction in diamniotic monochorionic and dizygotic twins

OBJECTIVE: Our purpose was to study fetal growth and blood flow distribution in diamniotic monochorionic compared with dizygotic (diamniotic dichorionic) twins by use of Doppler velocimetry of the umbilical artery and middle cerebral artery. STUDY DESIGN: Study candidates were divided into group A, consisting of 33 pairs (66 fetuses) of diamniotic monochorionic twins, and group B, 50 pairs (100 fetuses) of diamniotic dichorionic twins. Diamniotic monochorionic placentation was confirmed by microscopic placental examination for group A. Diamniotic dichorionic placentation was ensured for group B by selecting only twins with different-sex pairs (dizygotic twins). Targeted ultrasonography with biometry was performed in each twin, and Doppler recordings of the umbilical artery and middle cerebral artery were obtained. Waveforms were analyzed and the systolic/diastolic ratio, the resistance index, and a measure of blood flow redistribution (brain-sparing effect), the cerebral/placental ratio, was calculated for each fetus. Growth status at birth was assessed by the number of small-for-gestational-age infants (≤10th percentile), low-birth-weight infants (≤25th percentile), and percent of growth discordance between twins. Intertwin differences were assessed by Δ values (value of larger twin minus value of smaller twin). RESULTS: Diamniotic monochorionic compared with dizygotic twins demonstrated a significantly greater probability of blood flow redistribution. For the study population as a whole, the brain-sparing effect was noted in 67% of small-for-gestational-age babies and only 7% of non-small-for-gestational-age infants (p ≤ 0.001). For the diamniotic monochorionic pregnancies blood flow redistribution occurred in 6 of 10 small-for-gestational-age infants (60%) and 6 of 46 non-small-for-gestational-age infants (13%). In the diamniotic monochorionic group small-for-gestational-age compared with non-small-for-gestational-age infants were more likely to show blood flow redistribution, which was the result of significantly decreased resistance in the middle cerebral artery and significantly increased resistance in the umbilical artery. Small-for-gestational-age infants (≤10th percentile) occurred much less frequently in the dizygotic group. Two of two small-for-gestational-age infants in the dizygotic group showed blood flow redistribution. Although the extremes of birth weight were more common in the diamniotic monochorionic group, both groups had relatively large numbers of small babies with birth weights in the lower 25th percentile (50.0% for diamniotic monochorionic and 44.0% for dizygotic twins, not significant). However, 42.3% (11/26) of diamniotic monochorionic twins who were in the low-birth-weight group showed blood flow redistribution compared with only 3.3% (1/30) whose birth weights were ≥25th percentile (p ≤ 0.001). In the dizygotic twins 10% of lower-birth-weight infants redistributed blood flow compared with 1% in the higher-birth-weight group, a nonsignificant difference. Diamniotic monochorionic compared with dizygotic twins were delivered earlier (32.9 weeks vs 34.8 weeks, p ≤ 0.001), were smaller (1832 gm vs 2304 gm, p ≤ 0.001), showed higher birth weight discordance (29.8% vs 14%, p ≤ 0.05), and had greater numbers (19.7% vs 2.3%, p ≤ 0.01) of infants at ≤10th percentile birth weight. CONCLUSIONS: Diamniotic monochorionic twins from the lower-birth-weight groups more often show blood flow redistribution compared with dizygotic twins of similar low birth weights. Placental vascular connections and the attendant hemodynamic changes in the fetuses of diamniotic monochorionic twins probably account for this difference. Brain-sparing events occur commonly without clinical twin transfusion syndrome in this group. These findings have implications for management. (Am J Obstet Gynecol 1998;178:1359-67.)     

Doppler assessment of umbilical artery blood flow for the prediction of outcome in fetal cardiac abnormality

Summary. In a series of 244 pregnancies referred for fetal echocar-diography, the umbilical artery waveform was also studied by pulsed Doppler ultrasound. In 152 normal pregnancies diastolic flow in the umbilical artery was always detectable after 20 weeks gestation. In 4 of 58 normal patients examined before 20 weeks, diastolic flow was absent in some part of the recording. In 34 fetuses with congenital heart disease detected at between 18 and 37 weeks gestation, 10 were found consistently to have associated absent diastolic flow. Five of these fetuses died in utero between 5 and 21 days after the recording; three were aborted and the remaining two died in the neonatal period at 4 and 7 days after the examination. Fetal congenital heart disease with normal umbilical blood flow also had a poor prognosis in general, but the adverse outcome was much less immediate than in fetuses with absent diastolic flow. No correlation was found between the type of congenital heart disease and the characteristics of the umbilical artery waveform. Absent diastolic flow in the umbilical artery indicates a poor short-term prognosis for fetuses with congenital heart disease, particularly after 20 weeks, when fetal death is predictable.