Investigation of intraplacental villous arteries by Doppler flow imaging in growth-restricted fetuses

OBJECTIVE: The purposes of our study were to assess the ability of color and power Doppler sonography to depict the blood flow in the intraplacental villous arteries and to evaluate whether the blood flow of intraplacental villous arteries in a normal pregnancy is different from that in a pregnancy that is associated with intrauterine growth restriction. STUDY DESIGN: Eighty-five women with uncomplicated pregnancy and 16 women with intrauterine growth-restricted fetuses between 27 and 38 weeks of gestation were examined by color and power Doppler imaging. The blood flow of intraplacental villous arteries was analyzed comparatively. The pulsatility index and peak systolic velocity were measured. RESULTS: A unit of 1 intraplacental villous artery-1 and its branches were seen as 1 cotyledon by color and power Doppler imaging. The cotyledon was easily identified and counted. Each cotyledon contained only 1 intraplacental villous artery-1. This method can visualize the intraplacental villous artery-1 to intraplacental villous artery-4 in normal pregnancies. The terminal villous arteries beyond intraplacental villous artery-4 were not imaged. The number of detectable intraplacental villous artery-1 in 1 placenta in intrauterine growth restriction was significantly lower than that in normal pregnancy. The number of detectable branches in intrauterine growth restriction was also significantly lower than in normal pregnancy. No intraplacental villous artery-4 blood flow was found in women with intrauterine growth restriction. In examined arteries, pulsatility index decreased and peak systolic velocity increased significantly with advancing gestational age (P <.02). At any given gestational age, pulsatility index and peak systolic velocity in the peripheral arteries were significantly lower than those in the upstream arteries in normal pregnancy (P <.001). The pulsatility index value of each intraplacental villous artery was also lower than that of the umbilical artery in the women with intrauterine growth restriction (P <.05). There were no differences in pulsatility index in each artery between the groups, although there were a few high pulsatility index values in intrauterine growth restriction. CONCLUSION: Color Doppler and power flow sonography are valuable tools for the detection of the blood flow of intraplacental villous arteries. The decrease in the number of detectable intraplacental villous artery-1 and branches was associated with intrauterine growth retardation.     

Fetal blood velocity waveforms in uncomplicated pregnancy

Umbilical artery velocity waves were measured in fetuses from 94 normal pregnant women. In all, 183 determinations were carried out from the 14th to the 40th week of gestation. A combination of pulsed echo and real-time scanning was used to obtain blood waveforms from the umbilical arteries. The umbilical artery velocity wave can be readily differentiated from other fetal signals by its pattern. The systolic peak of the velocity wave was divided by the end diastolic value, thereby giving an S/D ratio. The S/D ratio in normal pregnancy declined from 7.6 to 2.0 from 14 to 40 weeks. Analysis of these waveforms indicated that the placenta is an organ of low vascular resistance and that placental resistance to blood flow declines with advancing gestational age in normal pregnancy. The umbilical artery S/D ratio provides a new and non-invasive marker of fetoplacental blood flow resistance.     

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.     

Umbilical artery and uteroplacental blood flow velocity waveforms in normal pregnancy--a cross-sectional study

Umbilical and arcuate artery blood flow velocity waveforms (FVW) were recorded in 125 normal singleton pregnancies from 20 to 42 weeks of gestation. The FVW were analysed for pulsatility index (PI), peak systolic velocity/minimum diastolic velocity ratio (S/D ratio), rising slope (RS) and descending slope (DS). Both in the umbilical and arcuate arteries, values for all variables declined with advancing gestation, indicating decreasing placental vascular resistance. The umbilical artery PI was unaffected by the fetal heart rate, but the arcuate artery PI was negatively correlated to the maternal heart rate (r = -0.40). The arcuate artery PI decreased by 0.00394 with each beat per minute increase in maternal heart rate. Normal limits (mean +/- 2 SD) were established for umbilical artery PI corrected for gestational age, and arcuate artery PI corrected for gestational age and maternal heart rate.     

Ultrasound of the placenta: a systematic approach. Part II: functional assessment (Doppler)

Doppler velocimetry is the ideal clinical tool to assess placental performance in high-risk pregnancies. It also has value in predicting later complications and outcome in pregnancies which appear uncomplicated. All three circulations (fetal, placental and maternal) may be interrogated by Doppler technology. In the following review, we present basic physics aspects of Doppler and discuss mainly Doppler investigation of the fetal-placental circulation (umbilical artery, intraplacental circulation) as well as the uterine arteries. The assessment of umbilical blood flow provides information on blood perfusion of the fetal-placental unit. The diastolic blood flow velocity component in umbilical artery increases with advancing gestation. In pregnancies complicated by placental dysfunction, there may be a reduction in the number of functional villi and/or small blood vessels with, as a result, increased impedance, reflected, mainly, by a decrease in end-diastolic velocity. When the resistance increases even more, there is no diastolic forward velocity (absent end-diastolic velocity). Further increase in the resistance causes reversed end-diastolic velocity, which is considered a late step in the cascade of events leading to intrauterine fetal demise. Doppler assessment of the umbilical arteries was found to improve outcome of high-risk pregnancies, and reduce hospital admissions. On the contrary, routine Doppler ultrasound in low risk or unselected populations does not seem to confer benefit on mother or newborn. Uterine artery Doppler is a useful test in predicting pregnancies at high risk of developing complications related to uteroplacental insufficiency. It identifies women who may benefit from increased antenatal surveillance or prophylactic therapy. Three-dimensional power Doppler sonography can provide new insights into placental pathophysiology.     

Volumetric flow in the umbilical artery: normative data

OBJECTIVE: Provide normative data for the volumetric blood flow (cc/min and cc/min/kg) in the umbilical artery. METHODS: Flow was determined from an umbilical artery in 252 normal obstetrical patients from 18-40 weeks' gestation utilizing pulsed Doppler and color flow Doppler with an angle of insonation of 30-60 degrees. Simultaneous velocimetry studies (S/D ratio, resistance and pulsatility indices), fetal biometry, and an anatomic survey were obtained to further define the normal population. RESULTS: There was a steady increase in the flow (cc/min) in the umbilical artery as pregnancy progressed. Flow/kg showed a steady decline as fetal weight increased. Umbilical artery diameter increased until reaching a plateau at 32-34 weeks. Velocimetric results were consistent with known data. CONCLUSIONS: Volumetric blood flow in the umbilical artery can be determined with relative ease and normative data from 18-40 weeks is presented for the first time.     

脐血流测定对脐带绕颈的产时监护

目的 :研究脐血流测定对脐带绕颈的产时监护作用。方法 :对 5 5 0例单胎足月妊娠孕妇进行脐血流测定 ,其中脐带绕颈 138例。分A、B、C 3组 ,分析其产时胎儿宫内窘迫发生率 (简称 :胎窘率 )及剖宫产率 ,并动态观察 14 0例(其中脐带绕颈 5 2例 ,无绕颈 88例 )产妇 ,产程中的脐血流变化。结果 :3组脐带长度、绕颈周数、新生儿Apgar评分 ,差异无显著性 (P >0 0 5 )。B组与C组的产时胎窘率及剖宫产率均较A组高 (P <0 0 1,P <0 0 5 )。产程中 ,S/D升高 >0 1,有脐带绕颈组明显高于无绕颈组 (P <0 0 1) ,S/D >3 0与 2 70 相似文献   

The effects of ritodrine infusion on fetal myocardial function and fetal hemodynamics

The effects of ritodrine infusion on fetal myocardial function and fetal hemodynamics were studied in 18 singleton, healthy, pregnant women with premature uterine contractions. Ritodrine was given intravenously for 2 1/2 h. In 10 cases both M-mode echocardiographs of the fetal heart and measurements of the blood flow in the fetal descending thoracic aorta were made before and after the infusion. No changes took place in the functional parameters or ventricular size of the fetal heart during the infusion. Fetal heart rate increased significantly. In the aorta both the volumetric flow and time-averaged systolic peak, mean and end-diastolic velocities increased significantly, while there were no changes in wave-form indices. In 8 other cases, blood velocity waveform indices were measured by color Doppler flow mapping from the fetal middle cerebral, renal and umbilical arteries. During the infusion the waveform indices decreased significantly in the middle cerebral and renal arteries. There was no change in the indices of the umbilical artery. Ritodrine did not cause any unfavorable changes in the fetal myocardial function or blood flow in the aorta and umbilical artery. The decreased waveform indices in fetal middle cerebral and renal arteries might indicate decreased vascular resistance in these vessels.     

Fetal middle-cerebral and umbilical artery flow assessments after glucose challenge test.

OBJECTIVE: To determine whether a change occurs in fetal middle-cerebral and umbilical artery flow after glucose challenge testing. METHOD: Fetal middle-cerebral and umbilical artery flow was assessed by Color Dopppler technology in 21 pregnant patients before and after the 50-g glucose challenge test. The resistance index (IR) was evaluated separately for each vessel. Statistical significance was determined by Chi-square test and repeated measurement analysis with two co-variates. RESULTS: After glucose ingestion the RI was significantly decreased in the middle-cerebral artery, but not in the umbilical artery. A significant increase in RI was recorded in the umbilical artery when maternal plasma glucose level exceeded 102 mg%. CONCLUSION: Maternal ingestion of glucose significantly alters blood flow velocimetry in the fetal middle-cerebral and umbilical arteries. These changes may lead to the misinterpretation of normal results. It is therefore recommended that sonographic flow velocimetry assessment not be performed early after concentrated glucose ingestion.     

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.     

Doppler velocimetry in patients with preeclampsia

Doppler velocimetry is a fast and convenient method for monitoring of fetal well being in high risk pregnancies. Doppler velocimetry is more specific and sensitive method of fetal surveillance than cardiotocography. The study's objective is to prove Doppler's effectiveness in predicting perinatal outcome in preeclamptic pregnancies. A retrospective study is designed, including pregnant women, diagnosed with preeclampsia, admitted to Maternity hospital "Majchin dom" for ten years. Doppler study was made and results were correlated to Apgar score, umbilical artery pH and base excess of the neonate at delivery. A correlation between RI of umbilical artery, uterine arteries and Apgar score at 5th minute was demonstrated. In severe cases correlation between RI of umbilical artery and neonatal pH was found. CONCLUSION: Doppler velocimetry is an effective method of fetal surveillance in pregnancies, complicated by preeclampsia     

Doppler investigation of the fetal circulation

Doppler ultrasound provides a non-invasive method for the study of fetal haemodynamics. Animal studies on effects of hypoxia have provided evidence of a redistribution of cardiac output to favour perfusion of the fetal heart, adrenals and brain, at the expense of the carcass, gut and kidneys. This paper summarises the changes in fetal Doppler parameters with advancing gestation. Furthermore, it examines the alterations in fetal haemodynamics in relation to fetal blood oxygen tension in samples obtained by cordocentesis from small for gestational age (SGA) fetuses. In SGA fetuses increased downstream impedence to flow in the umbilical artery, as demonstrated by the absence of end-diastolic frequencies in the flow velocity waveforms (FVW), is associated with fetal hypoxia. This presumably reflects the underlying derangement of placental structure and function. The impedence to flow and mean blood velocity were also measured in FVWs from the descending thoracic aorta and common carotid artery, obtained by pulsed Doppler ultrasound, and from the middle cerebral and renal arteries obtained by colour flow imaging. There were significant correlations between the degree of fetal hypoxia and alterations in Doppler parameters, which were compatible with the brain sparing effect. Thus, in fetal hypoxia impedence to flow in the common carotid and middle cerebral arteries was decreased, whereas impedence in the aorta and renal artery was increased. There were simultaneous alterations in the mean blood velocity in the opposite direction to those in impedence.     

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.     

Prenatal ultrasonographic diagnosis of conditions associated with potential umbilical cord compression

The objective of this review is to assess the current literature pertaining to prenatal ultrasonographic diagnosis of various conditions that predispose the fetus to potential umbilical cord compression. We performed a MEDLINE search utilizing the terms:umbilical cord compression, nuchal cord, cord entanglement, and true knot. Additional sources were obtained through cross-referencing. Prenatal ultrasound assists in the diagnosis of nuchal cord(s), true knot of the umbilical cord, cord entanglement in monoamniotic twin gestations, and other unusual etiologies that may lead to umbilical cord compression. Supplementary ultrasonographic measures including color Doppler imaging, Doppler flow velocimetry, and possibly three-dimensional ultrasound may further prenatal diagnosis of these conditions. Doppler flow velocimetry may also assist in detecting impaired or deteriorating umbilical artery flow reflecting increasing cord compression prior to the onset of adverse and potentially nonreversible effects upon the fetus. Close fetal surveillance in cases further complicated by decreased fetal movements, decreased amniotic fluid volume, postdates, fetal growth restriction, and impaired umbilical artery Doppler flow velocimetry may assist in the management of such gestations. Although definitive prospective studies investigating neonatal outcome following prenatal ultrasonographic depiction of potential umbilical cord compression are not currently available, review of the literature suggests that increased fetal surveillance may be indicated in certain clinical conditions.     

Uteroplacental Doppler flow velocity waveform indices in normal pregnancy: a statistical exercise and the development of appropriate reference values.

In a prospective cross-sectional study, we examined 154 normal pregnant women and measured the systolic to diastolic (S/D) ratio and resistance index (RI) in the umbilical artery and both uterine arteries. Placental location with respect to laterality was determined by real-time ultrasound. In patients with unilateral placental location, each uterine artery was evaluated according to its relationship with the placenta. Doppler flow velocity waveforms were obtained by a continuous wave Doppler device. Kolmogorov D tests revealed that RI values follow gaussian distribution, but that S/D values were markedly skewed to the right. There was a significant negative linear relationship between gestational age and umbilical artery RI and a significant negative curvilinear relationship between gestational age and umbilical artery (S/D (r = 0.83, p less than 0.001; and r = -0.79, p less than 0.001, respectively). Confidence bands for umbilical artery RI were developed based on the linear model with gestational age (fitted umbilical artery RI = 0.97199 - 0.01045*gestational age). Confidence bands for umbilical artery S/D were derived from the corresponding RI values by means of the functional relationship S/D = 1/(1 - RI). The RI and S/D values of the uterine arteries declined until 24 to 25 weeks' gestation and remained unchanged thereafter. This relationship, however, was not statistically significant (r = -0.10, p = 0.22). The placental uterine artery is different from the nonplacental quantitatively and qualitatively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of maternal exercise on fetal umbilical artery waveforms

Twenty-one nulliparous women in the last trimester of pregnancy gave their informed verbal consent to undergo an acute exercise test. Fetal umbilical artery velocimetry waveforms were measured to monitor the effect of exercise on fetal umbilical artery blood flow. The mean gestational age was 32 weeks (range 28-37 weeks). The mean exercise intensity was 71% of submaximal exercise (range 67-74%). Maternal heart rate rose significantly (P less than 0.001) from a mean of 83 to 138 beats per min. Following moderate exercise, the systolic over the diastolic ratio (S/D) decreased significantly (P less than 0.001) after 2 and 20 min. This indicates a decrease in umbilical blood flow resistance and an improved placental circulation following exercise in healthy women. We conclude that maternal exercise does not appear to be harmful to the mother or her fetus at this level of exercise intensity in healthy individuals.     

The application of uterine and umbilical artery velocimetry to the antenatal supervision of pregnancies complicated by maternal sickle hemoglobinopathies

To assess the efficacy of Doppler flow velocimetry in predicting fetal compromise and neonatal outcome in pregnant women with sickle cell hemoglobinopathies, a prospective study was conducted of 96 patients, 48 with sickle cell hemoglobinopathy (8 with SS and 40 with AS hemoglobin) and 48 low-risk AA hemoglobin controls. All subjects were followed biweekly from the third trimester of pregnancy through delivery with uterine and umbilical artery velocimetry, nonstress, tests, and hematocrit and blood pressure measurements. An abnormal systolic/diastolic ratio was defined as a value greater than or equal to 3. The incidence of abnormal systolic/diastolic ratios for uterine or umbilical arteries was significantly higher in pregnant women with SS hemoglobin (88%) when compared with patients with AS (7%) and AA (4%) hemoglobin. In addition, the abnormal systolic/diastolic ratios for both umbilical and uterine arteries are correlated with abnormal nonstress test results. The nonstress test results became abnormal on average 3 weeks after the systolic/diastolic ratios did. The presence of abnormal systolic/diastolic ratios for umbilical and uterine arteries is predictive of fetal distress and infants small for gestational age. The high incidence of concordant uterine and umbilical artery abnormal systolic/diastolic ratios in pregnant women with SS hemoglobinopathy, which were identified earlier than were abnormal nonstress results, suggests an important parameter in the monitoring of these high-risk pregnancies.     

New score indicating placental vascular resistance

BACKGROUND: Umbilical artery Doppler velocimetry is a routine method for fetal surveillance in high-risk pregnancy. Uterine artery Doppler seems to give comparable information, but it can be difficult to interpret as there are two arteries, which might show notching and/or increased pulsatility index (PI) as signs of increased vascular impedance. Combining the information on vascular resistance on both sides in a new score might simplify and improve evaluation of placental circulation. METHODS: Uterine and umbilical artery Doppler velocimetry was evaluated in 633 high-risk pregnancies. The managing clinician was informed only about the umbilical artery flow. The umbilical artery flow spectrum was semiquantitatively divided into four blood flow classes (BFC), expressing signs of increasing vascular resistance. The uterine artery Doppler flow spectrum was divided into five uterine artery scores (UAS), taking into account presence/absence of notching and/or increase in PI. By adding UAS to BFC, a new placental score (PLS) was constructed with values ranging from 0 to 7, indicating general placental vascular resistance. The scores were related to three outcome variables: small-for-gestational age (SGA), premature delivery (<37 weeks), and cesarean section. RESULTS: All three score systems showed a significant relationship between signs of increasing vascular resistance and outcome. The new PLS showed the best association to adverse outcomes, with optimal cut-off at values exceeding score 3. CONCLUSION: Doppler velocimetry on both sides of the placenta showed a strong relationship to an adverse outcome of pregnancy. The new PLS showed a better relationship to adverse perinatal outcome than the BFC and the UAS. The PLS can simplify evaluation of uteroplacental and fetoplacental Doppler velocimetry.     

Adrenomedullin is increased in the fetoplacental circulation in intrauterine growth restriction with abnormal umbilical artery waveforms

OBJECTIVE: To examine whether adrenomedullin, a novel vasoactive peptide produced by the placenta, participates in the uteroplacental hemodynamic alterations in intrauterine growth restriction, we studied the correlation between adrenomedullin levels and fetoplacental blood flow. STUDY DESIGN: Maternal and umbilical blood samples were collected in pregnancies complicated by intrauterine growth restriction with abnormal umbilical artery Doppler findings and in control pregnancies. Adrenomedullin levels were measured by means of a specific radioimmunoassay, and flow velocimetry waveforms were recorded from uterine, umbilical, and fetal middle cerebral arteries. RESULTS: Mean adrenomedullin values in umbilical plasma were higher (P <.05) in patients with intrauterine growth restriction (63.7 +/- 34.2 pg/mL; n = 16) than in control subjects (38.1 +/- 14.8 pg/mL; n = 16). A significant correlation was found between maternal adrenomedullin levels and umbilical artery pulsatility index. Moreover, fetal adrenomedullin concentrations correlated negatively with middle cerebral artery pulsatility index and positively with umbilical artery pulsatility index/middle cerebral artery pulsatility index ratio. CONCLUSION: This study provides evidence that adrenomedullin is increased in fetuses with intrauterine growth restriction in response to reduced uteroplacental blood flow and suggests that it may participate in the fetal hemodynamic modifications.     

The application of color power angiography to the longitudinal quantification of blood flow volume in the fetal middle cerebral arteries, ascending aorta, descending aorta, and renal arteries during gestation

OBJECTIVE: This study was undertaken to determine by means of color power angiography the longitudinal changes in the diameters and the flow volumes of 4 major fetal arteries during gestation. STUDY DESIGN: The middle cerebral artery, the ascending aorta, the descending aorta, and the renal arteries in 81 appropriate-for-gestational-age fetuses were examined longitudinally between 24 and 38 weeks' gestation by means of color power angiography. In addition to measurement of the diameters of these arteries, Doppler velocimetry was performed. Flow volume was calculated from the cross-sectional areas of the arteries and the velocity integral of the Doppler waveforms. RESULTS: The mean (+/-SD) gestational age at delivery and birth weight were 39.8 +/- 1. 6 weeks and 3326 +/- 345 g, respectively. The diameters and flow volumes of all the arteries increased significantly as gestational age advanced. Flow volume increased from 39 +/- 19.0 mL/min to 140 +/- 63.9 mL/min in the middle cerebral artery, from 216.2 +/- 77.6 to 937.4 mL/min in the ascending aorta, from 124.4 +/- 76.6 to 390.0 mL/min in the descending aorta, and from 27.5 +/- 16.8 to 80.3 +/- 57.3 mL/min in the renal arteries. When blood flow volume was adjusted to milliliters per kilogram body weight, an initial significant fall in blood flow was seen in all the vessels to a minimal level at 30 weeks' gestation; blood flow rose thereafter, although not significantly, until term. The ratios of flow volume in the ascending aorta to those in the other vessels increased with gestation, with the highest ratio being that between the ascending aorta and the renal arteries. CONCLUSION: Identification of fetal arteries with color power angiography is easy and highly sensitive. The distributions of blood flow in various fetal arteries exhibited regional differences, with significantly more blood flow to the brain. These normative baseline values may be useful in the diagnosis of congenital cardiac anomalies and also in the diagnosis and monitoring of fetuses with intrauterine growth restriction.