[Doppler sonographic determination of specific hemodynamic changes in fetal circulation during the last four weeks before birth].

The observation of characteristic flow changes measured by Doppler ultrasound in the fetal descending aorta a short time before delivery led us to systematically analyse our measurement data. For the retrospective analysis, records with a total of 115 measurements taken in the last four weeks prior to spontaneous onset of labour from 90 women with normal pregnancies were used. For each of the four weekly periods there were between 15 and 50 measurements. Both qualitative and quantitative flow parameters were evaluated. The findings showed: 1. No significant changes in the blood flow characteristics of the uteroplacental and fetoplacental vessels; 2. A clear widening of the diameter of the aorta; 3. A decrease in the mean flow velocity in the descending aorta; 4. A steep decrease in maximum velocity during late systole, sometimes so pronounced that a notch in the flow envelope was observed. The time when the changes occurred was found to be 2 weeks prior to spontaneous onset of labour. These changes in the fetal circulation, which can be called "term effect", occur along with other developments taking place towards the time of birth. They are probably related to the beginning of spontaneous contractions and indicate an adaptation to the changing supply conditions occurring a few days before the onset of labour.