Proximity of term labor deepens the fall of Doppler impedance in the fetal cerebral arteries

ABSTRACT

Objective: To determine the existence of Doppler changes in the fetal vertebral, middle cerebral and umbilical arteries prior to term labor.

Methods: Five hundred and twenty eight Doppler examinations of the vertebral (VA), middle cerebral (MCA) and umbilical (UA) arteries resistance indices (RI) were performed between 37 and 41 weeks gestation. For each artery, values were converted into multiples of the median (MoM) and were divided into four groups according to the interval to labor and compared using Kruskal–Wallis tests. Subsequently, values were plotted in scattergrams and linear regressions and 95% confidence intervals were calculated. Finally, using multivariate analysis and model averaging, the importance and interrelationship of Doppler measurements in the explanation of the interval to labor was evaluated.

Results: Univariate and multivariate analysis confirmed that, independently of gestational age, fetuses examined close to labor presented more intense Doppler changes in the cerebral arteries with a significant reduction of the VA RI and MCA RI. This reduction was larger in the MCA. No significant changes were detected in the UA.

Conclusion: Before the onset of term labor, the fetal cerebral flow presents an additional reduction of impedance, which is more intense in the MCA system.     

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.     

Assessment of nitrite oxide and maternal–fetal Doppler parameters during pregnancy

Objective: The objective was to evaluate and compare the whole blood nitrite concentration in the three trimesters of pregnancy. Additionally, we investigate whether there is any relation between nitrite concentrations and Doppler ultrasound analysis of some maternal and fetal vessels.

Methods: Thirty-three healthy pregnant women were examined at the first (11–14 weeks), second (20–24 weeks) and third trimester (34–36 weeks) of pregnancy. In the three exams, we determined the maternal whole blood nitrite concentration and uterine arteries Doppler analysis to determine pulsatility index (PI), and resistance index (RI). In the second and third trimester we also performed fetal umbilical and middle cerebral arteries PI and RI. We compared the concentrations of nitrite in three trimesters and correlated with Doppler parameters.

Results: No difference was observed in the whole blood nitrite concentrations across trimesters: 151.70?±?77.90?nmol/ml, 142.10?±?73.50?nmol/ml and 147.10?±?87.30?nmol/ml; first, second and third trimesters, respectively. We found no difference in correlation between whole blood nitrite concentration and Doppler parameters from the evaluated vessels.

Conclusions: In healthy pregnant women, the nitrite concentrations did not change across gestational trimesters and there was also no strong correlation with Doppler impedance indices from maternal uterine arteries and fetal umbilical and middle cerebral arteries.     

Fetal blood velocity waveforms in normal pregnancies. A longitudinal study

Blood velocity in the umbilical artery, fetal descending aorta and fetal middle cerebral artery was recorded by means of 3.5 MHz pulsed Doppler ultrasound in 22 normal pregnancies. The measurements were performed longitudinally between 25 and 42 weeks of gestation. The maximum blood velocity curves were analysed for pulsatility index (PI), systolic/diastolic velocity ratio (S/D ratio) and in the middle cerebral artery also for the resistance index according to Pourcelot (RI). In the umbilical artery, all variables decreased significantly with increasing gestational age as an expression of the decreasing placental vascular resistance. PI in the descending aorta remained fairly constant during the examined period of gestation. In the middle cerebral artery, all three variables (PI, S/D ratio, RI) decreased significantly as gestation advanced. With the exception of the umbilical artery at 28-32 weeks, PI and S/D ratio were not influenced by the heart rate in any of the vessels examined. Diagrams of the gestational age-related reference values (means +/- 2 SD) for the variables of the blood velocity waveforms were established. Additionally, a ratio of the PI and S/D was calculated for the umbilical artery and middle cerebral artery.     

硝酸甘油对高危妊娠胎儿—胎盘血流动力学的影响

应用Acuson-128彩色电脑声像仪监测12例高危妊娠孕妇应用硝酸甘油前后的脐动脉、胎儿大脑中动脉,胎儿腹主动脉的血流动力学变化。结果:用药后脐动脉的搏动指数(PI),阻力指数(RI)和S/D值均显著降低(P<0.001),胎儿大脑中动脉和胎儿腹主动脉的PI、RI和S/D值无显著改变,呈现良好的耐受性,表明应用硝酸甘油可明显降低脐-胎盘血管阻力,是改善胎儿血氧供应的简便、有效方法,并对硝酸甘油的作用机理进行了讨论。     

Farbkodierte Dopplersonographie — Normwerte des Widerstandsindex in Abhängigkeit vom Gestationsalter

The examination of fetal circulation by means of Doppler ultrasound has clinical potential. In order to use the indices that characterize the waveform, it is important to establish reference ranges throughout pregnancy and to determine the natural variations. This paper sets out to fulfill these requirements. The study was performed in 139 patients with singleton pregnancies between 29 and 41 weeks’ gestation. Patients with no previous obstetric complications and no apparent medical problems were approached at the time of their visit to the antenatal clinic. All examinations were performed by a single observer. A 3-MHz pulsed waved duplex Doppler ultrasound instrument was used (Quantum 2000; Siemens, Erlangen, Germany). Doppler blood flow velocity waveforms in the umbilical artery, fetal aorta and middle cerebral artery were recorded. For each artery, reference ranges and a standard curve were performed for the resistance index (RI). The RI of the umbilical and the middle cerebral artery showed a continuing fall during gestation, but the resistance index of the fetal descending aorta did not change during gestation. The finding that the RI changes as gestation progresses indicates that fetal circulation increases throughout pregnancy. This suggests a decreasing placental resistance during normal gestation. Study of fetal circulation may identify patients at risk of developing severe disorders, thus allowing possible preventive therapy. Knowledge of the reference ranges helps to discriminate between a normal situation and mild or severe forms of disease.     

Fetal intracranial arterial hemodynamics assessed by color and pulsed Doppler ultrasound.

Fetal intracranial arterial velocimetries were serially performed on 31 pregnant women with regular menstrual cycle, at 28-40 weeks of gestation, using color and pulsed Doppler ultrasound. The change in fetal intracranial arterial hemodynamics was based on the calculation of resistance index (RI). There was no significant difference between the RI values in the anterior cerebral artery (ACA) and middle cerebral artery (MCA) from 28 weeks to term. The RI in the posterior cerebral artery (PCA) was significantly lower than that in the ACA and MCA, respectively, from 28 weeks to term (P less than 0.001). The PI values in both the ACA and MCA remained unchanged from 28 to 33 weeks, became significantly lower from 34 to 35 weeks (P less than 0.05), and the values were fairly constant thereafter. The RI seen in the PCA showed no significant change from 28 weeks to term. This color and pulsed Doppler ultrasound assessment of fetal intracranial arterial blood flow provides a useful foundation for elucidating normal intracranial hemodynamics and will aid in avoiding misinterpretations of the different intracranial arteries.     

The impact of low-dose aspirin therapy on umbilical and middle cerebral artery blood flow in pregnancy complicated by idiopathic intrauterine growth restriction

AIM: Intrauterine growth restriction and its treatment still constitute a major clinical problem in perinatology. Since low doses of aspirin could improve the utero-placental circulation (by shifting the prostacyclin/thromboxane A2 balance), we have evaluated the impact of low-dose aspirin treatment of IUGR during pregnancy on umbilical (UA) and middle cerebral artery (MCA) blood flow. MATERIAL AND METHODS: The study comprised 32 pregnant women with idiopathic fetal intrauterine growth restriction (IUGR) diagnosed during pregnancy on the basis of ultrasound examination of biometric parameters (BPD, FL, AC). All the patients were treated only by low-dose aspirin (1.5 mg/kg) for 8-14 days. The: fetal biometry and calculation of blood flow indices (S/D, RI, PI) in umbilical and middle cerebral artery were performed before and after treatment. RESULTS: Mean values of all biometric parameters of the fetuses measured before and after treatment did not show statistically important differences (AC-borderline significantly). Umbilical artery blood flow indices calculated after the treatment were slightly lower and MCA indices slightly higher, as compared to those before the treatment. Cerebro-placental ratio changed from 1.37 to 1.63 (borderline significantly). CONCLUSIONS: IUGR treatment by low-dose aspirin had beneficial but non-significant impact on umbilical and middle cerebral artery blood flow. Since the number of subjects in this study was relatively small, further clinical studies are necessary to evaluate the effectiveness of IUGR treatment by low dose aspirin.     

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)     

Nonobstructive dilatation of the fetal bowel in twin gestations. A possible sonographic marker for fetal compromise

OBJECTIVE: To assess the possible association of in-utero bowel dilatation and circulatory changes with fetal compromise. METHODS: A retrospective survey of all ultrasound examinations was performed at the Chaim Sheba Medical Center (n approximately 10,000) between 1995 and 1999. Cases with ultrasonographic evidence of bowel dilatation, but without evidence of obstruction, were recruited. In utero Doppler studies of umbilical, splenic, superior mesenteric arteries, and middle cerebral artery (MCA) were performed: systolic/diastolic ratio (S/D), pulsatility index (PI) and resistance index (RI) were calculated in the above arteries and compared with those of normal fetuses. Nonstress test and cord blood pH were also assessed. Neonatal medical records were procured. RESULTS: Four fetuses, all of who were products of twin gestations, showed bowel dilatation without evidence for obstruction. Three of the four fetuses were small-for-gestation-age (SGA) and of bichorionic gestation, while one was of monochorionic twin gestation, with twin transfusion syndrome. In all three SGA fetuses, Doppler studies revealed increased peripheral resistance in the umbilical artery and adaptive peripheral vasodilatation in the fetal midcerebral, splenic and superior mesenteric arteries. In all cases, an abnormal nonstress test led to prompt delivery. CONCLUSIONS: Acute fetal bowel dilatation in a twin gestation is associated with abnormal splanchnic and gut perfusion that may lead to fetal compromise.     

Components of variability of umbilical arterial Doppler velocimetry--a prospective analysis

This study prospectively analyzed the components of variance and error contributions of umbilical arterial Doppler indices in a normal pregnant population (308 women) with gestational ages ranging from 27 to 40 weeks. A continuous-wave Doppler instrument with a 4 MHz transducer was used. The Doppler indices measured were systolic/diastolic ratio, diastolic/average ratio, pulsatility index, and resistance index. The contributions of gestational age, fetal heart rate, location of measurement, interobserver variability, and intraobserver variability on the variance were studied. The investigation demonstrated that the gestational age and fetal heart rate contributed to 33% to 46% and 15% to 18% of the variance, respectively. The location of the Doppler measurement contributed to 29% to 46% of the error variance. Additionally, the interobserver and intraobserver error variance amounted to 10% to 14% and 5% to 9%, respectively. Of these various factors, the interobserver and intraobserver variance were related to the nonhemodynamic phenomena and therefore represented error components. It is obvious that these factors that affect the variance of the Doppler indices should be considered before the diagnostic reliability of this technique can be critically evaluated.     

Variation in Doppler indices along the length of the cord from the intraabdominal to the placental insertion

AIM. The aim of this study was to assess the feasibility of obtaining umbilical artery Doppler waveforms from the intraabdominal portion (perivesical) of the umbilical arteries and to compare the indices from this site to those from the free loop (FL) of cord placental insertion (PL) and abdominal insertion (AI). METHODS. A cross-sectional study of 71 singleton fetuses of 24-38 weeks of gestation. Umbilical artery Doppler waveforms were obtained from four sites by a single operator and their resulting indices--i.e. resistance index, pulsatility index, and systolic/diastolic ratio--were compared. Waveforms were also obtained from the two perivesical (PVC) arteries and the mean was used for analysis. Statistical analyses were performed using appropriate non-parametric tests. RESULTS: Doppler waveforms acceptable for inclusion in the study were obtained in 100% of cases from the FL site. There were failures to obtain waveforms that met the inclusion criteria in three (4%) cases at the PL site, three (4.2%) cases at the PVC site, and 12 (16.9%) cases at the AI. The three indices fell progressively with gestation from the PVC to the PL sites. There were no significant differences between the two PVC arteries using non-parametric test of mean difference for related samples using Wilcoxon signed-rank test (P > 0.05) for all the indices. The relation between the differences at the two ends of the cord was fairly consistent across gestation. CONCLUSIONS: Doppler velocimetry at PVC site of the umbilical artery is feasible and easy to perform. The indices obtained at this site are higher than those at the other three sites. There is a need for standardization of the site of sampling in order to ensure consistency for clinical application.     

Acute effects of maternal smoking on fetal hemodynamics.

OBJECTIVE: To investigate acute effects of cigarette smoking on fetal hemodynamics. METHOD: Sixty seven women between 32nd to 40th weeks of gestation were evaluated. Maternal blood pressure and heart rate, fetal heart rate (FHR) tracing, umbilical and fetal middle cerebral arterial (MCA) color Doppler measurements were evaluated. Pre- and postsmoking results were compared with paired t-test. RESULTS: Maternal heart rate significantly increased after smoking. Baseline FHR and FHR variability remained unchanged. The number of participants who had a reactive NST was 60 in 67 before smoking (89.5%) and decreased to 47 after smoking (70.1%) (p=0.009). There were no significant changes between maximum and minimum flow velocities, pulsatility index (PI), resistance index (RI) and systolic/diastolic flow ratio (S/D) of umbilical and middle cerebral arteries. CONCLUSION: The nicotine load of a single cigarette may be inadequate to cause a detectable decrease in utero-placental blood flow; however, smoking prior to the FHR recording may alter the FHR reactivity.     

Relationship between doppler velocimetry at middle cerebral artery and umbilical artery and status of newborn after delivery

OBJECTIVES: Aim of research was estimation of correlation between doppler parameters and fetal state after delivery. MATERIAL AND METHODS: One hundred fifty-one pregnancies treated in Dept. of Obstetrics and Gynecology of Medical Academy in Bydgoszcz was investigated between 1998-2002. Pregnancies were estimated between 27 and 43 Hbd. Ultrasound examination using pulse and color Doppler was performed (ACUSON XP 128) and PI, RI, S/D, MCA, UA were estimated. DESIGN: Following doppler parameters were analyzed: pulsatile index (PI), resistance index (RI) and systolic/diastolic ratio (S/D) in middle cerebral artery (MCA) and in umbilical cord artery (UA). The newborn children were estimated by Apgar score in first minute of life (AP1). Correlation between amount of amniotic fluid index (AFI) and newborn state in first minute after delivery was investigated too. RESULTS: There were following correlations in this investigation: (1) negative between UA PI and AP1 (-0.26); (2) negative between UA RI and AP1 (-0.23); (3) negative between UAS/D and AP1 (-0.16); (4) negative between AFI and API (-0.06); (5) lack of statistical correlation between MCA PI, MCA RI, MCA S/D and AP1. We considered following covariancies: (1) negative between AFI and AP1 (-1.03); (2) negative between UA S/D and AP1 (-0.42); (3) negative between UA PI and AP1 (-0.23); (4) negative between UA RI and AP1 (-0.09). CONCLUSIONS: We concluded that Doppler investigations by measure of parameters of blood flow in umbilical cord artery (PI, RI, S/D) can be predictive to fetal threat and useful in estimation of newborn state.     

The value of doppler velocimetry of umbilical and middle cerebral arteries in pregnancy complicated by diabetes mellitus

Fifty-three diabetic pregnant treated in Dpt of Obstetrics and Perinatology in Lublin were investigated. The paper presents correlations between metabolic parameters in diabetic patients and Doppler welocimetry in umbilical and middle cerebral arteries and also analyses way of delivery and outcomes. Correlations between fetal Doppler parameters and metabolic status of mothers have been found. We estimate that Doppler velocimetry hasn't prognostic value in predicting of fetal distress.     

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.     

The effect of methyldopa treatment on uterine,umblical and fetal middle cerebral artery blood flows in preeclamptic patients

The purpose of this study was to evaluate the efficacy of methyldopa in the treatment of preeclamptic patients. This study was performed on 24 preeclamptic women who were in between 25–36 weeks of gestational age. 24 healthy pregnant women were taken as control group. Before starting treatment, 24 preeclamptic patients were examined with Doppler ultrasound. Pulsatility index, resistance index, systolic/diastolic ratio of uterine, umblical and fetal middle cerebral arteries were measured. Preeclamptic patients were treated with totally 1 g methyldopa per day. After 7 d, patients were reexamined with Doppler ultrasound. The effect of methyldopa on uterine, umblical and fetal middle cerebral artery blood flows were detected. Only one control with Doppler ultrasound was done to the healthy pregnant women. Before methyldopa treatment to the preeclamptic women, pulsatility index (PI), resistance index (RI) and systolic/diastolic ratio (S/D) on uterine and umblical arteries were significantly higher than the control group. However, fetal middle cerebral artery (MCA) values were significantly lower than the control group. When Doppler results of preeclamptic patients before and after the methyldopa treatment were compared, no significant differences in terms of Pulsatility Index, Resistance IndexI and S/D ratio of umblical and fetal middle cerebral arteries were found. However, the results of uterine artery were significantly lower after the treatment in preeclamptic patients. Treatment with methyldopa lowered the uterine artery resistance in preeclamptic patients but did not effect the resistance of umblical and fetal middle cerebral artery. Received: 27 March 2001 / Accepted: 5 June 2001     

Prolonged morphine exposure in utero causes fetal and placental vasoconstriction: a case report.

Vasoconstriction was observed in the fetal middle cerebral and umbilical arteries by Doppler assessment at 27 weeks gestation in a patient requiring continuous morphine infusion for pain control. Fetal heart tracings were also concerning. Fetal status improved after a change to fentanyl infusion, a shorter acting opioid. Caution is recommended when long-term chronic narcotic infusion is used in pregnancy.     

The effect of loading dose of magnesium sulfate on uterine,umbilical, and fetal middle cerebral arteries Doppler in women with severe preeclampsia: A case control study

IV MgSO₄ administration in women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices.

Objective: To evaluate Doppler parameters of the umbilical artery (UmA), uterine artery (UA), and fetal middle cerebral artery (MCA) before and after MgSO₄ administration in women with severe preeclampsia. Methods: A case control study included 100 pregnant women with severe preeclampsia. Umbilical artery, uterine artery, and fetal middle cerebral artery Doppler were measured before and 20 minutes after intravenous administration of 6 g of magnesium sulfate. Results: There was a significant difference between maternal systolic blood pressure (173.20 ± 22.72 vs. 156.60 ± 19.18), diastolic blood pressure (109.60 ± 9.14 vs. 101.90 ± 10.05), and heart rate (80.52 ± 11.52 vs. 88.48 ± 12.08) before and after administration of MgSO₄ in the studied patients (p value < 0.001). There was a significant difference between umbilical artery, middle cerebral artery, and uterine artery Doppler parameters before and after administration of MgSO₄ in the studied patients (p value < 0.001). There was no significant difference between umbilical artery/middle cerebral artery with regard to RI and PI. However, there was significant difference with regard to the S/D ratio (p value < 0.001). The decrease in the values of Doppler parameters before and after administration of MgSO₄ was more in the middle cerebral artery than in the umbilical artery. Conclusion: Intravenous administration of magnesium sulfate in pregnant women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices with reduced resistance to blood flow in these vessels.