Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 66

Doppler ultrasound depends upon the ability of a pulsed ultrasound beam to be changed in frequency when encountering moving objects such as red blood cells (RBC). The change in frequency (Doppler shift) between the emitted reflected beams is proportional to the velocity of the RBC and dependent on the angle between the ultrasound beam and the vessel. Pulsed‐wave Doppler velocimetry provides a flow velocity waveform from which information can be obtained to determine three basic characteristics of blood flow that are useful in obstetrics: velocity, resistance indices, and volume blood flow. Doppler velocimetry is applied in a broad number of clinical circumstances in high‐risk pregnancies including diagnostic fetal echocardiography, fetal growth restriction (FGR), fetal anemia, adverse pregnancy outcome assessment, twin‐twin transfusion syndrome (TTTS), twin anemia polycythemia sequence (TAPS), and preterm labor (ductus arteriosus assessment for indomethacin tocolysis). Pulsed‐wave Doppler velocimetry is also used to evaluate the ductus venosus (DV) in first‐trimester risk assessment for Down syndrome but is not discussed in this protocol.