1201: Fetal aortic blood flow velocity waveform: Effect of gestational age and its sampling points

Abstract

Fetal arterial blood flow velocity waveforms of umbilical artery or middle cerebral artery have been widely used for estimation. Fetal descending aortic flow was used for fetal estimation and the end-diastolic reversed flow or absent end-diastolic flow of descending aorta was reported as those of umbilical arterial flow. But the umbilical arterial flow waveforms are more easily acquired than those of descending aorta, and recently the latter has not been used for fetal estimation. Otherwise, fetal descending aorta is able to be visualized linearly by 2D ultrasonography, and the blood flow velocity itself is able to be measured accurately when adequate insonation angle is acquired. Evaluation of fetal blood flow velocity might be useful tool for the fetal cardiac function. We cross-sectionally examined fetal descending aortic blood flow velocity waveforms from 551 normal singleton fetuses between 18 to 41 weeks of gestation in order to establish the reference values the Doppler indices (resistance index and maximum systolic velocity) and to clarify the characteristics of fetal aortic flow velocity waveform. Doppler flow velocity waveforms were acquired from three different sampling points: thoracic (behind fetal heart), upper abdominal (just below diaphragm) and lower abdominal (just below the origination of renal arteries) portions in each fetus. The resistance indices for the fetal descending aorta decreased from thoracic to lower abdominal portion, but no remarkable change was detected during fetal development (0.84 ± 0.05, 0.79 ± 0.04, 0.76 ± 0.05, thoracic, upper abdominal and lower abdominal, respectively, at 18 to 19 weeks of gestation, and 0.85 ± 0.03, 0.81 ± 0.02, 0.73 ± 0.05 at 40 to 41 weeks). Otherwise, maximum systolic velocity decreased from central to peripheral portion and increased during fetal development (69 ± 11, 58 ± 10, 49 ± 8 cm/s, thoracic, upper abdominal and lower abdominal, respectively, at 18 to 19 weeks of gestation, 134 ± 13, 112 ± 18, 92 ± 12 cm/s at 40 to 41 weeks). Moreover, fetal descending aortic flow velocity waveforms sometimes revealed systolic multiple peaks pattern and/or early-diastolic reversed flow patterns. These characteristic flows were more frequently observed in late third trimesters. Interestingly, they were more frequently observed at thoracic portion than at lower abdominal portion. There were no fetuses that revealed these characteristic flows at 18 to 19 weeks of gestation. But, multiple systolic peaks patterns were detected at thoracic, upper abdominal and lower abdominal portions in 64.3%, 42.8% and 35.7% of fetuses at 40 to 41 weeks of gestation. We also detected 9.1%, 3.6% and 1.8% of fetuses at 37 to 38 weeks of gestation at thoracic, upper abdominal and lower abdominal portions, respectively. In conclusion, we resulted that the Doppler flow velocity waveforms are affected by the sampling points on the fetal descending aorta. The resistance index and the maximum systolic velocity for the descending aorta gradually decrease from the thoracic to the lower abdominal portion. These changes are obviously detected throughout the course of pregnancy after 18 weeks of gestation.