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Abstract
Doppler ultrasound has many types and many applications in obstetrics. It is well known now that fetal venous and cardiac Doppler are now used side to side with arterial Doppler.
The most common studied vessels are; umbilical artery, uterine artery, middle cerebral artery, aorta, inferior vena cava, ductus venosus, umbilical vein with flow velocity waveforms at the level of atrio-ventricular valves.
Doppler studies of the fetal circulation in intra uterine growth retardation and fetal hypoxia have demonstrated increased resistance to flow in the umbilical arteries and redistribution in the fetal circulation with increased velocity in the middle cerebral artery presented by decreased PI in in the MCA. It was noticed that in the first stages of the disease, there is a preferential shift of cardiac output in favour of the left ventricle, leading to improved cerebral perfusion, but with deterioration in the fetal condition, there is a decline in cardiac output and progressive worsening in cardiac function . Normal venous flow suggests continuing fetal compensation, whereas abnormal flow indicates the breakdown of hemodynamic compensatory mechanisms. An abrupt increase in pulsatility of ductus venosus waveforms with loss of forward flow velocity during atrial contraction precede the onset of pathological fetal heart rate patterns and decreased short-term variation.
Increased impedance to flow in the uterine arteries at 20-24 weeks of gestation in both high-risk and low-risk pregnancies is associated with increased risk for subsequent development of pre-eclampsia and intrauterine growth restriction. In pregnancies with increased impedance to flow in the uterine arteries, prophylactic treatment with low-dose aspirin or vitamins C and E may reduce the risk for subsequent development of pre-eclampsia.