Increased vascular resistance in the descending aorta of the human fetus in hypoxia.

Blood velocity waveforms from the fetal thoracic aorta, obtained by a combination of real-time and Doppler ultrasound and a spectral analyser, detected a total end-diastolic block in the curve in nine pregnancies with chronic fetal hypoxia. Simultaneous cardiotocographic recordings were normal except in one patient. These findings suggest that hypoxia causes an increase of peripheral vascular resistance in the tissues distal to the thoracic aorta and that this change appears earlier than pathological changes in the cardiotocogram. The potential clinical value of this technique justifies further research.