Placental doppler microvasculature in normal and abnormal pregnancy

Abstract

Superb microvascular imaging (SMI) is a new ultrasound Doppler technique that enables the assessment of fine and low-velocity blood flow profiles. This article reviews the sonographic anatomy of the normal placental microvasculature using SMI and the clinical applications for evaluating pathological conditions during pregnancy. The basal plate shows a single layer of blood flow with decidual flows and flows extending into the placenta, on which arterial Doppler waveforms can be detected, indicating jet flows from the spiral arteries into the intervillous space. Several studies have demonstrated the potential for diagnosing the placenta accreta spectrum based on direct SMI findings, including missing decidual tissues and direct invasion of the placenta into the myometrium in the lesion. In a normal pregnancy, the placental villous flows show tree forms by SMI, which is considered blood flow embedded in the stem villi. Because the stem villi provide mechanical stability for the villous trees and control autoregulation of the fetoplacental blood flow in the peripheral villi, the abnormal vasculature characteristics observed by SMI reflect morphological changes in the placenta and dysfunction of the peripheral villous vessels, such as fetal/maternal malperfusion of the placenta.