Methodology and basic problems related to blood flow studies in the human fetus.

A method was developed for non-invasive measurement of human fetal blood flow. The method combines real-time ultrasonography with 2 MHz pulsed Doppler technique. The blood flow is calculated from the blood velocity, estimated from the Doppler spectrum, and the vessel diameter, measured in the real-time image. Time-distance recording was applied for measurements of the pulsatile diameter changes in the fetal aorta. The method proved to possess a good accuracy and reproducibility when tested in vitro experiments and in a comparison with electromagnetic flow measurements in animals. Possible sources of error were analysed and recommendations for minimizing the risk of errors are presented.