A continuous wave Doppler ultrasound method of recording fetal breathing in utero

Intra-uterine fetal breathing can be measured using 2 MHz continuous wave Doppler ultrasound to monitor the fluctuations in venous return which are associated with the pressure changes induced by fetal breathing activity. This article describes the technique for locating the transducer on the maternal abdomen and the sounds that are heard, together with the instruments necessary for recording, processing and displaying the signal.