Wave reflections in the umbilical artery measured by Doppler ultrasound as a novel predictor of placental pathology

Abstract

BackgroundThe umbilical artery (UA) Doppler pulsatility index is used clinically to detect elevated feto-placental vascular resistance. However, this metric is confounded by variation in fetal cardiac function and is only moderately predictive of placental pathology. Our group developed a novel ultrasound methodology that measures wave reflections in the UA, thereby isolating a component of the Doppler signal that is specific to the placenta. The present study examined whether wave reflections in the UA are predictive of placental vascular pathology.MethodsStandard clinical Doppler ultrasound of the UAs was performed in 241 pregnant women. Of these, 40 women met narrowly defined preset criteria for the control group, 36 had maternal vascular malperfusion (MVM) and 16 had fetal vascular malperfusion (FVM). Using a computational procedure, the Doppler waveforms were decomposed into a pair of forward and backward propagating waves.FindingsCompared to controls, wave reflections were significantly elevated in women with either MVM (p<0.0001) or FVM pathology (p = 0.02). In contrast, the umbilical and uterine artery pulsatility indices were only elevated in the MVM group (p<0.0001) and there were no differences between women with FVM and the controls.InterpretationThe measurement of wave reflections in the UA, combined with standard clinical ultrasound parameters, has the potential to improve the diagnostic performance of UA Doppler to detect placental vascular pathology. Identifying women with FVM pathology is particularly challenging prenatally and future investigations will determine if women at risk of this specific placental disease could benefit from this novel diagnostic technique. The umbilical artery (UA) Doppler pulsatility index is used clinically to detect elevated feto-placental vascular resistance. However, this metric is confounded by variation in fetal cardiac function and is only moderately predictive of placental pathology. Our group developed a novel ultrasound methodology that measures wave reflections in the UA, thereby isolating a component of the Doppler signal that is specific to the placenta. The present study examined whether wave reflections in the UA are predictive of placental vascular pathology. Standard clinical Doppler ultrasound of the UAs was performed in 241 pregnant women. Of these, 40 women met narrowly defined preset criteria for the control group, 36 had maternal vascular malperfusion (MVM) and 16 had fetal vascular malperfusion (FVM). Using a computational procedure, the Doppler waveforms were decomposed into a pair of forward and backward propagating waves. Compared to controls, wave reflections were significantly elevated in women with either MVM (p<0.0001) or FVM pathology (p = 0.02). In contrast, the umbilical and uterine artery pulsatility indices were only elevated in the MVM group (p<0.0001) and there were no differences between women with FVM and the controls. The measurement of wave reflections in the UA, combined with standard clinical ultrasound parameters, has the potential to improve the diagnostic performance of UA Doppler to detect placental vascular pathology. Identifying women with FVM pathology is particularly challenging prenatally and future investigations will determine if women at risk of this specific placental disease could benefit from this novel diagnostic technique. Research in Context Evidence before this studyPlacental vascular pathology is a causal factor in a large proportion of pregnancy complications. A key component of fetal health assessment is measurement of the pulsatility of the umbilical artery blood velocity waveforms using Doppler ultrasound, an indirect measurement of feto-placental vascular resistance. However, the umbilical artery pulsatility index is confounded by physiological variables such as the fetal heart rate and is only moderately predictive of placental pathology. We have developed a novel ultrasound methodology called wave reflection analysis that isolates the portion of the pulsation that is specific to the placenta. In healthy pregnancies, we have shown the pulsation of the umbilical artery waveform is explained by the presence of wave reflections. Added value of this studyIn this study, we recruited 241 pregnant women for wave reflection analysis using standard obstetric ultrasound equipment and placental pathology assessment. We demonstrated that wave reflections in the umbilical artery are significantly elevated in women with maternal and fetal vascular placental pathology compared to healthy controls. Implications of all the available evidenceThese findings have the potential to extend the utility of umbilical artery Doppler to improve diagnosis of placental pathologies. This is particularly promising for fetal vascular malperfusion where there is currently no reliable method of detection prenatally. Wave reflections arise from transitions in biomechanical properties of blood vessels, and finding strong reflections in pathologic pregnancies provides a mechanistic link between abnormal Doppler waveforms and vascular pathology. Placental vascular pathology is a causal factor in a large proportion of pregnancy complications. A key component of fetal health assessment is measurement of the pulsatility of the umbilical artery blood velocity waveforms using Doppler ultrasound, an indirect measurement of feto-placental vascular resistance. However, the umbilical artery pulsatility index is confounded by physiological variables such as the fetal heart rate and is only moderately predictive of placental pathology. We have developed a novel ultrasound methodology called wave reflection analysis that isolates the portion of the pulsation that is specific to the placenta. In healthy pregnancies, we have shown the pulsation of the umbilical artery waveform is explained by the presence of wave reflections. In this study, we recruited 241 pregnant women for wave reflection analysis using standard obstetric ultrasound equipment and placental pathology assessment. We demonstrated that wave reflections in the umbilical artery are significantly elevated in women with maternal and fetal vascular placental pathology compared to healthy controls. These findings have the potential to extend the utility of umbilical artery Doppler to improve diagnosis of placental pathologies. This is particularly promising for fetal vascular malperfusion where there is currently no reliable method of detection prenatally. Wave reflections arise from transitions in biomechanical properties of blood vessels, and finding strong reflections in pathologic pregnancies provides a mechanistic link between abnormal Doppler waveforms and vascular pathology.

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