In 12 pregnant mothers fetal sounds and infrasounds were recorded by means of a new compliance matched transducer and compared with a simultaneous ultrasound record of fetal activity. A defined pattern on the fetal phonograph correlated with 86% of the total fetal breathing detected with ultrasound, and a further distinctive pattern was associated with 90% of fetal movements. Examination of the fetal phonocardiogram when the fetus was breathing showed a significant increase in the short-term variability of both the systolic and diastolic times when compared with non-breathing episodes. The median amplitude variabilities for both the first and the second heart sounds were also significantly increased during fetal breathing. Measurement of fetal sounds and infrasounds with a compliance matched transducer offers a non-invasive method for assessment of fetal activity for long periods of time.
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