Normative values of Doppler velocimetry of five major fetal arteries as determined by color power angiography

Assessing the external validity and clinical relevance of umbilical doppler resistance index references in daily practice

OBJECTIVE

To assess the external validity and clinical relevance of current references for umbilical artery resistance index (UA RI) in daily practice.

METHODS

Retrospective cross-sectional single center study including all UA RI measurements between 22 and 40 gestational weeks (GW) from distinct patients between 2014 and 2022. Patients with normal pregnancies and normal neonatal outcomes that had an UA RI measurement between 2014 and 2019 were used to calculate reference ranges. The established reference for the 95th centile was compared to two current references. The clinical relevance of the established reference was tested by comparing neonatal outcomes according to the 95th percentile among the consecutive distinct patients between 2020 and 2022.

RESULTS

Among the 13342 consecutive distinct patients with a singleton pregnancy that had an UA RI measurement between 22 and 40 GW between 2014 and 2022, 5298 patients were included to establish the reference ranges, and 3634 patients to validate these ranges. For each gestational age, the established references were similar to current references. Using the established references, the proportion of patients presenting an UA RI>95th percentile among the patients with normal pregnancies in the validation population was comparable to the proportion when using the two current references. Among the validation population, 268 patients (7.4 %) (95%CI[6.5-8.2]) presented an UA RI ≥ 95th percentile. Of these 268 patients, 67.9% had a SGA newborn (versus 19.2%, p<0.001) and 59% a preterm birth (versus 13.9%, p<0.001).

CONCLUSIONS

The reference range obtained from daily practice is clinically relevant and similar to current references.

Fetal renal artery blood flow - Normal ranges

INTRODUCTION

The study objectives were to develop standard charts for fetal renal artery blood flow to define normal ranges and to assess the reliability of the measurements.

METHODS

This prospective, longitudinal study reviewed 72 low-risk singleton pregnancies who had serial ultrasound examinations. Pulse wave Doppler was used to obtain the resistivity and pulsatility indices of the fetal renal arteries. Standard charts of the fetal renal arteries were created using mixed effects modelling and the intra- and interobserver reliability for the renal blood flow measurements was analysed.

RESULTS

Standard charts of the normal ranges of the renal artery resistive index (RI) and pulsatility index (PI) of the fetal renal arteries were created. The 3rd, 5th, 10th, 50th, 90th, 95th and 97th centiles were calculated. The intraclass correlation coefficient was acceptable for intraobserver reliability (RI = 0.66, PI = 0.88) and poor for interobserver reliability (RI = 0.11, PI = -0.56).

CONCLUSIONS

These novel charts demonstrate the change of the fetal renal artery blood flow during pregnancy. These may be used in clinical practice to detect variations from these normal ranges and be useful in future studies of kidney function projection.

Use of the Renal Artery Doppler to Identify Small for Gestational Age Fetuses at Risk for Adverse Neonatal Outcomes

Objective: To measure the sensitivity and positive predictive value (PPV) for an adverse neonatal outcome among growth-restricted fetuses (FGR) comparing the cerebral–placental ratio (CPR) with the cerebral–renal ratio (CRR). Methods: Retrospective analysis of 92 women who underwent prenatal ultrasound at the University of Maryland and the University of Padua. Renal, middle cerebral and umbilical artery Doppler waveforms were recorded for all scans during the third trimester. The last scan prior to delivery was included for analysis. We calculated the test characteristics of the pulsatility indices (PI) of the umbilical and renal arteries in addition to the derived CPR and CRR to detect a composite adverse neonatal outcome. Results: The test characteristics of the four Doppler ratios to detect increased risk for the composite neonatal outcome demonstrated that the umbilical artery pulsatility index had the best test performance (sensitivity 64% (95% CI: 47–82%), PPV 24% (95% CI: 21–27), and positive likelihood ratio 2.7 (95% CI: 1.4–5.2)). There was no benefit to using the CRR compared with the CPR. The agreement between tests was moderate to poor (Kappa value CPR compared with CRR: 0.5 (95%CI 0.4–0.70), renal artery PI:−0.1 (95% CI −0.2–0.0), umbilical artery PI: 0.5 (95% CI 0.4–0.7)). Only the umbilical artery had an area under the receiver operating curve that was significantly better compared with the CPR as a reference (p-value < 0.01). Conclusions: The data that we present do not support the use of renal artery Doppler as a useful clinical test to identify a fetus at risk for an adverse neonatal outcome. Within the various indices applied to this population, umbilical artery Doppler performed the best in identifying the fetuses at risk for an adverse perinatal outcome.

Normative references and clinical correlates of fetal umbilical artery Doppler indices in southwestern Nigeria

OBJECTIVE

To derive normative references for umbilical artery (UA) Doppler indices, including pulsatility index (PI), resistance index (RI), and systolic/diastolic (SD) ratio, for singleton pregnancies in Ile-Ife, Nigeria, and compare them with reference values from other populations.

METHODS

A longitudinal study involving 415 women with a singleton fetus at 26-40 gestational weeks attending Obafemi Awolowo University Hospital, Ile-Ife, between July 2015 and March 2019. Fetal UA PI, RI, and SD ratio were measured every 4 weeks until delivery. Reference values from the 2.5th to the 97.5th centiles were derived from 1375 measurements. Correlations between indices and bio-demographic characteristics were assessed; regression equations were generated.

RESULTS

The RI, PI, and SD ratio decreased by 0.013, 0.027, and 0.71, respectively, for each additional week of pregnancy. There was a negative correlation between the three indices and birthweight (P<0.001), but not maternal parity, age, or fetal gender. Regression equations for RI, PI, and SD ratio were, respectively, 1.004 - 0.013x, 1.78 - 0.027x, and 4.77 - 0.71x, where x is gestational age (weeks).

CONCLUSION

The derived normative references for fetal UA Doppler indices are recommended for monitoring high-risk pregnancies in Nigeria. The indices are comparable to those derived from Norwegian, Thai, and British cohorts.

Reference ranges for Doppler indices of umbilical and fetal middle cerebral arteries and cerebroplacental ratio: systematic review

OBJECTIVE

To assess studies reporting reference ranges for umbilical artery (UA) and fetal middle cerebral artery (MCA) Doppler indices and cerebroplacental ratio (CPR), using a set of predefined methodological quality criteria for study design, statistical analysis and reporting methods.

METHODS

This was a systematic review of observational studies in which the primary aim was to create reference ranges for UA and MCA Doppler indices and CPR in fetuses of singleton gestations. A search for relevant articles was performed in MEDLINE, EMBASE, CINAHL, Web of Science (from inception to 31 December 2016) and references of the retrieved articles. Two authors independently selected studies, assessed the risk of bias and extracted the data. Studies were scored against a predefined set of independently agreed methodological criteria and an overall quality score was assigned to each study. Linear multiple regression analysis assessing the association between quality scores and study characteristics was performed.

RESULTS

Thirty-eight studies met the inclusion criteria. The highest potential for bias was noted in the following fields: 'ultrasound quality control measures', in which only two studies demonstrated a comprehensive quality-control strategy; 'number of measurements taken for each Doppler variable', which was apparent in only three studies; 'sonographer experience', in which no study on CPR reported clearly the experience or training of the sonographers, while only three studies on UA Doppler and four on MCA Doppler did; and 'blinding of measurements', in which only one study, on UA Doppler, reported that sonographers were blinded to the measurement recorded during the examination. Sample size estimations were present in only seven studies. No predictors of quality were found on multiple regression analysis. Reference ranges varied significantly with important clinical implications for what is considered normal or abnormal, even when restricting the analysis to the highest scoring studies.

CONCLUSIONS

There is considerable methodological heterogeneity in studies reporting reference ranges for UA and MCA Doppler indices and CPR, and the resulting references have important implications for clinical practice. There is a need for the standardization of methodologies for Doppler velocimetry and for the development of reference standards, which can be correctly interpreted and applied in clinical practice. We propose a set of recommendations for this purpose. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Multidimensional fetal flow imaging with cardiovascular magnetic resonance: a feasibility study

PURPOSE

To image multidimensional flow in fetuses using golden-angle radial phase contrast cardiovascular magnetic resonance (PC-CMR) with motion correction and retrospective gating.

METHODS

A novel PC-CMR method was developed using an ungated golden-angle radial acquisition with continuously incremented velocity encoding. Healthy subjects (n = 5, 27 ± 3 years, males) and pregnant females (n = 5, 34 ± 2 weeks gestation) were imaged at 3 T using the proposed sequence. Real-time reconstructions were first performed for retrospective motion correction and cardiac gating (using metric optimized gating, MOG). CINE reconstructions of multidimensional flow were then performed using the corrected and gated data.

RESULTS

In adults, flows obtained using the proposed method agreed strongly with those obtained using a conventionally gated Cartesian acquisition. Across the five adults, bias and limits of agreement were - 1.0 cm/s and [- 5.1, 3.2] cm/s for mean velocities and - 1.1 cm/s and [- 6.5, 4.3] cm/s for peak velocities. Temporal correlation between corresponding waveforms was also high (R~ 0.98). Calculated timing errors between MOG and pulse-gating RR intervals were low (~ 20 ms). First insights into multidimensional fetal blood flows were achieved. Inter-subject consistency in fetal descending aortic flows (n = 3) was strong with an average velocity of 27.1 ± 0.4 cm/s, peak systolic velocity of 70.0 ± 1.8 cm/s and an intra-class correlation coefficient of 0.95 between the velocity waveforms. In one fetal case, high flow waveform reproducibility was demonstrated in the ascending aorta (R = 0.97) and main pulmonary artery (R = 0.99).

CONCLUSION

Multidimensional PC-CMR of fetal flow was developed and validated, incorporating retrospective motion compensation and cardiac gating. Using this method, the first quantification and visualization of multidimensional fetal blood flow was achieved using CMR.

Evaluation of the predictive value of fetal Doppler ultrasound for neonatal outcome from the 36th week of pregnancy

Background

Early prediction of adverse neonatal outcome would be possible by Doppler impedance indices of middle cerebral artery (MCA), umbilical artery (UmA), and descending aortal artery (AO) that result in decrease neonatal morbidity and mortality rate. The aim of the present study was a determination of optimal value for the ratio of MCA to descending aorta blood flow (MCA/AO) impedance indices and its comparison with the ratio of MCA to UmA (MCA/UmA) impedance indices and their relationship with neonatal outcome.

Materials and Methods

This was a prospective cohort study on 212 pregnant women with gestational age 36 weeks or more, in three hospitals in Tehran, from April 2012 to April 2013. We investigated AO, MCA, and UmA impedance indices Doppler ultrasound every 2 weeks till delivery. The mother was monitored for adverse pregnancy outcome (hypertension [HTN], fetal growth retardation, and other maternal complications) then infant birth weight, cord blood of pH, and Neonatal Intensive Care Unit (NICU) admission during the first 24 h after delivery were assessed. Finally, we investigated relationships between Doppler indices and neonatal outcomes include neonatal body weight (NBW), cord blood of pH, and NICU admission.

Results

MCA/AO resistance index (RI) and MCA/AO pulsatile index (PI) showed an area under the receiver operating characteristics curve (area under the curve) of 0.905 (95% confidence interval (CI): 0.850, 0.959) and 0.818 (95% CI: 0.679, 0.956), respectively. The cutoff values for pH (≥7.2 vs. <7.2) based on MCA/AO RI and MCA/AO PI indices were 0.951 (sensitivity, 80% and specificity, 86%) and 0.853 (sensitivity, 91% and specificity, 83%), respectively. The cutoff value for NBW (≥2500 vs. <2500 g) based on MCA/UmA PI index was 1.467 (sensitivity, 73% and specificity, 63%). The cutoff value of NICU admission of child based on MCA/AO PI index was 1.114 (sensitivity, 73% and specificity, 54%).

Conclusion

In the end of third-trimester pregnancies with the assessment of MCA and AO artery Doppler ultrasonography, it is possible to prevent many cases of neonatal acidosis caused by prenatal asphyxia as well as inappropriate interventions which are applied on mother. If MCA/AO PI was <0.85, the fetus needs to be evaluated further because it is at risk for acidosis.

Doppler waveform patterns and reference ranges of fetal renal artery blood flow indices in normal Thai fetuses during the second trimester

Background

Fetal hemodynamics can be assessed by Doppler ultrasonography, but the normal Doppler waveform pattern and reference range of fetal renal artery blood flow indices in normal Thai fetuses during the second trimester have not been studied.

Objectives

To study the pattern and establish the normal reference range of fetal renal artery blood flow indices in the normal Thai fetus during the second trimester.

Materials and methods

This cross-sectional descriptive study included 512 normal singleton pregnant women, gestational age between 14(+0) and 28(+6) weeks. Ultrasonography was performed to assess the Doppler waveform pattern and estimate the normal reference range of fetal renal artery blood flow indices. All fetuses were delivered at term with normal outcomes at birth. The mean and 95th and 5th percentiles of the Doppler indices for each gestational week were estimated.

Results

Doppler patterns with absence of diastolic flow in the entire cardiac cycle (type I), and absence of diastolic flow at the end of cardiac cycle (type II) were presented in about 10.4% of normal fetuses during the second trimester of pregnancy. Values for pulsatility index, peak systolic velocity, systolic-to-diastolic ratio, and resistance index (with absent end-diastolic velocity (AEDV) removed) each increased significantly with gestational age. The increase in end-diastolic velocity (with AEDV removed) with gestational age was not significant.

Conclusion

These normative data could serve as a basis for evaluation of the fetal renal artery blood flow, which should be of benefit for pregnancy management, especially in situations that interfere with fetal renal perfusion.

Fetal Hemodynamic Parameters in Low Risk Pregnancies: Doppler Velocimetry of Uterine, Umbilical, and Middle Cerebral Artery

Objective. To elaborate curves of longitudinal reference intervals of pulsatility index (PI) and systolic velocity (SV) for uterine (UtA), umbilical (UA), and middle cerebral arteries (MCA), in low risk pregnancies. Methods. Doppler velocimetric measurements of PI and SV from 63 low risk pregnant women between 16 and 41 weeks of gestational age. Means (±SD) for intervals of gestational age and percentiles 5, 50, and 95 were calculated for each parameter. The Intraclass Correlation Coefficients (ICC) were also estimated for assessing intra- and intervariability of measurements. Results. Mean PI of UtA showed decreasing values during pregnancy, but no regular pattern was identified for mean SV. For UA, PI decreased and SV increased along gestation. MCA presented PI increasing values until 32–35 weeks. SV showed higher levels with increasing gestation. High ICC values indicated good reproducibility. Conclusions. Reference intervals for the assessment of SV and PI of UtA, UA, and MCA were established. These reference intervals showed how a normal pregnancy is expected to progress regarding these Doppler velocimetric parameters and are useful to follow high risk pregnancies. The comparison between results using different curves may provide insights about the best patterns to be used.

Longitudinal reference intervals for Doppler velocimetric parameters of the fetal renal artery correlated with amniotic fluid index among low-risk pregnancies

OBJECTIVE

To establish longitudinal reference intervals for pulsatility index (PI) and systolic velocity (SV) of the fetal renal artery, and to evaluate their correlation with the amniotic fluid index (AFI).

METHODS

A prospective longitudinal study was conducted among women with low-risk pregnancies who attended outpatient clinics at the University of Campinas Medical School, Brazil, at 16-19 weeks of pregnancy between April 1, 2008, and March 31, 2010. Doppler velocimetric measurements of the fetal renal artery and assessments of the AFI were undertaken at 4-week intervals to 36 weeks, and every 2 weeks thereafter until delivery.

RESULTS

A total of 63 women were enrolled. The PI of the fetal renal artery showed little variation during pregnancy, whereas SV values increased to 36-37 weeks of pregnancy and decreased thereafter. No correlations were found between the AFI and the fetal renal artery Doppler velocimetric parameters (P>0.05 for all). The intraclass correlation coefficients for intra-observer and inter-observer variability indicated good reproducibility of SV, but the reproducibility of PI was lower.

CONCLUSIONS

The AFI did not correlate with fetal renal artery Doppler velocimetric measures among low-risk pregnancies. However, investigations are needed among high-risk pregnancies.

Second- and third-trimester placental hemodynamics and the risks of pregnancy complications: the Generation R Study

Characteristics of the uterine and umbilical artery blood flow patterns are indirect measures of uteroplacental circulation. We examined whether uterine and umbilical artery resistance indices are influenced by maternal demographic and lifestyle characteristics, track from the second trimester to the third, and are associated with the risk of pregnancy complications. This analysis was embedded among 7,660 pregnant women in the Generation R Study (Rotterdam, the Netherlands, 2001-2005). Placental resistance indices were assessed in the second and third trimesters. Information about pregnancy outcomes was obtained from medical records. Maternal characteristics affected second- and third-trimester placental resistance indices. Correlation coefficients for correlation between the second and third trimesters were 0.50 and 0.32 for uterine artery resistance index and umbilical artery pulsatility index, respectively. Higher placental resistance indices in the second and third trimesters and persistence in the highest tertile of uterine artery resistance index from the second trimester to the third were associated with the risks of preeclampsia, preterm birth, and small size for gestational age at birth (all P's < 0.05). Our study shows that placental resistance indices are influenced by maternal demographic and lifestyle characteristics and track moderately from the second trimester to the third. Increased placental resistance indices in the second and third trimesters are associated with increased risks of adverse pregnancy outcomes.

The posterior part of the human cerebral arterial circle (CAC): arterial caliber from gestational weeks 13 to 24

Numerous studies have reported that all components of the cerebral arterial circle in the 4-month-old human fetus are more slender than adult vessels, and of equal caliber. After that period, a degree of caliber differentiation is present, especially at the level of the posterior communicating arteries. The aim of this study was to determine arterial diameters in the posterior part of the fetal cerebral arterial circle from the 4th month (IV) to the 6th (VI). One hundred and seventy-two fetal cerebral arterial circles were examined by means of a surgical microscope. It was determined that average diameters of the left (right) pre-communicating parts of the posterior cerebral artery ranged from 0.30 +/- 0.03 (0.29 +/- 0.02) mm in month IV, to 0.36 +/- 0.04 (0.36 +/- 0.03) mm during month V and up to 0.55 +/- 0.22 (0.50 +/- 0.18) mm in month VI. The average diameters of the left (right) posterior communicating artery ranged from 0.24 +/- 0.02 mm (0.25 +/- 0.02) in month IV, to 0.30 +/- 0.03 mm (0.29 +/- 0.05) during month V and up to 0.38 +/- 0.08 (0.44 +/- 0.10) in month VI. Gender differences between posterior cerebral artery and posterior communicating artery diameters were not significant. Average posterior cerebral artery diameters were significantly larger than posterior communicating artery diameters in months IV and V, but not in month VI. It was established that caliber differentiation in the posterior part of the cerebral arterial circle began from gestational month IV, and that gender differences in arterial diameters were not significant until month VI of gestation.

Abnormal arterial flows by a distributed model of the fetal circulation

Modeling the propagation of blood pressure and flow along the fetoplacental arterial tree may improve interpretation of abnormal flow velocity waveforms in fetuses. The current models, however, either do not include a wide range of gestational ages or do not account for variation in anatomical, vascular, or rheological parameters. We developed a mathematical model of the pulsating fetoumbilical arterial circulation using Womersley's oscillatory flow theory and viscoelastic arterial wall properties. Arterial flow waves are calculated at different arterial locations from which the pulsatility index (PI) can be determined. We varied blood viscosity, placental and brain resistances, placental compliance, heart rate, stiffness of the arterial wall, and length of the umbilical arteries. The PI increases in the umbilical artery and decreases in the cerebral arteries, as a result of increasing placental resistance or decreasing brain resistance. Both changes in resistance decrease the flow through the placenta. An increased arterial stiffness increases the PIs in the entire fetoplacental circulation. Blood viscosity and peripheral bed compliance have limited influence on the flow profiles. Bradycardia and tachycardia increase and decrease the PI in all arteries, respectively. Umbilical arterial length has limited influence on the PI but affects the mean arterial pressure at the placental cord insertion. The model may improve the interpretation of arterial flow pulsations and thus may advance both the understanding of pathophysiological processes and clinical management.