Study of fetal tracheal fluid velocities using Doppler ultrasound.

Objective: To characterize tracheal fluid flow during fetal breathing movements by Doppler ultrasound.

Study Design: To use pulsed Doppler to measure flow velocity during inspiration and expiration in a cross-sectional study of 15 normal fetuses and determine the correlation, if any, between flow velocity and gestational age.

Results: Cyclic respiratory profiles - both regular and irregular - were observed. Intratracheal flow velocity was very elevated during inspiration, ranging from 10 to 80 cm/s and from 5 to 20 cm/s during expiration.

Conclusion: This technique enables the noninvasive semiquantitative evaluation of fetal breathing movements. This Doppler application opens the field for future studies to characterize the extent of pulmonary hypoplasia.