Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 75

Blood flow velocity waveforms obtained by pulsed‐wave Doppler velocimetry change in any given fetal vessel across gestation. In the umbilical artery of a normal pregnancy, there is a progressive increase in diastolic flow velocity across gestation, which reflects a decrease in the resistance within the placenta. One characteristic of FGR due to uteroplacental insufficiency is an increase in blood flow resistance within the placenta, which can be detected by Doppler velocimetry upstream in the umbilical arteries. Approximately 40% of cardiac output is directed toward the placenta via the umbilical artery. Thus, as placental disease progresses and blood flow resistance increases, fetal hypoxia may be reflected in the central nervous system (CNS) and the heart is subject to increased workload (afterload). Prior to significant cardiac dysfunction becoming apparent, abnormalities arise in the “prechordial” venous circulation (inferior vena cava, DV, and hepatic veins) in up to 70% of preterm, severely FGR fetuses. Further, recent data from a randomized clinical trial suggest that use of DV to manage early‐onset FGR may reduce long‐term neurodevelopmental delay. Use of Doppler velocimetry in the management of FGR is further discussed in Protocol 41.