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Definitions
Abnormal uterine artery Doppler: defined as either an absolute cutoff (for example, resistance index >0.58), or a measurement greater than a particular centile of the reference range, and/or diastolic notching.
Angle-independent Doppler indices: reflect the degree of resistance to blood flow downstream of the interrogation site. Examples include S/D (systolic/diastolic) ratio, RI (resistance index), PI (pulsatility index).
Early diastolic notch: defined as a persistent decrease in blood flow velocity in early diastole, below the diastolic peak velocity.
Inhibin A: a member of the transforming growth factor β family, predominantly secreted by the placenta.
PAPP-A (pregnancy-associated plasma protein A): a large glycoprotein complex predominantly produced by the placenta.
Placental growth factor: a pro-angiogenic protein.
PP-13 (placental protein 13): a member of the galectin family predominantly expressed by the placenta.
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The Doppler effect is named after Johann Christian Andreas Doppler (1803 to 1853), an Austrian scientist who described the changing color of stars as they move closer or farther away from the earth. Doppler signals, traveling back towards the ultrasound transducer which emitted the sound, are composed of many frequency shifts, thus creating a complex waveform.
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Doppler velocimetry of the uteroplacental circulation is an important modality due to several reasons. It is a noninvasive diagnostic tool that provides insight and can assess resistance to blood flow in this circulation. It has been proposed as a screening test to identify women at high risk for the development of preeclampsia and small-for-gestational-age (SGA) fetuses. In addition, uterine artery Doppler has increasingly been used to screen for these disorders as early as the first trimester.
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In this chapter, we review the anatomy and development of the uteroplacental circulation, the pathologic changes associated with placental implantation failure, the rationale for using Doppler velocimetry to detect these changes, and the studies that examine the effectiveness of uterine artery Doppler velocimetry in the first and second trimesters to screen for adverse perinatal outcomes, such as preeclampsia and SGA.
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ANATOMY AND DEVELOPMENT OF THE UTEROPLACENTAL CIRCULATION
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Blood supply to the uterus is mainly provided by the uterine arteries, with a small contribution from the ovarian arteries. The uterine arteries are branches of the internal iliac artery. Upon reaching the isthmic portion of the uterus, they ascend through the lateral wall before anastomosing with the ovarian arteries at the cornu of the uterus (Figure 10-1).1 Blood supply to the anterior and posterior walls is provided by the arcuate arteries, which run circumferentially around the uterus. Radial branches extend from the arcuate arteries at right angles towards the endometrium, where they divide into 2 or more spiral arteries (Figure 10-2).2,3,4,5, and 6
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