[Ultrasound in the study of fetoplacental circulation]

Exploration of fetal vessels is performed with a duplex system which combines a real-time linear imaging system 3.5 MHz and a pulsed Doppler (2.5 MHz). The transducers of the imaging and Doppler systems are associated in the same probe. Umbilical and aortic circulation have been investigated on 100 pregnancies. The umbilical artery Doppler spectrum shows an important diastolic flow which increases all along the pregnancy. A decrease of this flow occurs when the placental circulatory resistances increase. In case of severe hypertension one can note a decrease or the disappearance of the diastolic flow related to the existence of vascular placental defects (infarctus). This was observed in pathological pregnancies with hypotrophy or fetal death. The placental resistances can be quantified with the Pourcelot index R = A - D divided by A, where A is the maximum systolic amplitude and D the maximum end diastolic amplitude, both measured on the umbilical artery spectrum. Fetal blood flow measurements were performed with the same device. The mean value of the blood flow is about 170 ml/min/kg in the aorta and 120 ml/min/kg in the umbilical arteries at the end of the pregnancy. The possibility to record simultaneously fetal aorta and inferior vena cava enable us to detect abnormal heart rate such as the atrioventricular block.