Invention of ultrasonic Doppler fetal actocardiograph and continuous recording of fetal movements

Aims To enable scientific studies on fetal movements and its relation to fetal heart rate directly detecting fetal chest motion with ultrasonic Doppler method. Methods A prototype of an ultrasonic Doppler fetal actocardiograph (ACG) was designed and handmade by the author. A 2 MHz ultrasound fetal heart rate (FHR) monitor was remodeled to detect fetal heartbeat and chest movement Doppler signals with a single ultrasound probe. The fetal movement Doppler signal was 20–50 Hz using 2 MHz ultrasound, separated from the fetal heartbeat Doppler signal, which was 100 or more Hz and sent to the autocorrelation FHR meter to record FHR curve, while fetal movement Doppler signals were detected through 20–80 Hz band‐pass filter, and changed to spikes recorded on a cardiotocography chart. Results The spike amplitudes of a moving steel ball expressed fetal movement on the ACG. FHR acceleration synchronized with fetal movement bursts. Fetal resting and active states are separated using the ACG. Fetal hiccupping movements on ACG were regular continuous spikes with 2–3 s intervals. Conclusion Fetal movements and hiccups were correctly recorded with the FHR curve. The relation of FHR and movement will be further clarified in future ACG readings.