Acceleration time of fetal arterial blood flow velocity waveforms: a preliminary study.

Background: Doppler ultrasonography has been widely used for fetal estimation, but most of them were estimated by the resistance and pulsatility indices. Acceleration time is one of parameters of flow velocity waveforms, but only few reports had discussed acceleration time of fetal circulation.

Methods: We analyzed Doppler flow velocity waveforms of fetal middle cerebral artery, descending aorta and abdominal umbilical artery obtained from 70 normal pregnant women between 18 and 40 weeks. Acceleration time was cross-sectionaly examined throughout pregnancy course.

Results: The acceleration times revealed no remarkable changes throughout pregnancy course in the middle cerebral artery, but significant increases were observed in the acceleration time of the descending aorta between 18-23 and 24-32 weeks. It also significantly decreased after 33 weeks compared to that of 18-32 weeks in the umbilical artery.

Conclusions: The acceleration time in fetal descending aorta is significantly shorter than that in the abdominal umbilical artery between 18 and 32 weeks of gestation. The umbilical arterial acceleration time apparently decreases throughout pregnancy course. Its values are almost double for that in the descending aorta between 18 and 23 weeks, but it becomes to be equal to the aortic acceleration time. The continuous decrease of the umbilical arterial acceleration time might be a result of a relative increase of placental flow.