The rhythmicity of fetal breathing varies with behavioural state in the human fetus

Abstract The rhythmicity of human fetal breathingmovements was studied during two different behavioural states (1F and 2F, respectively), using real-time B-scan-directed M-mode ultrasound recordings. The mean breath-to- breathinterval durations and the standard deviations(SD), and the standard deviationsof the interval differences (SDDSI) were calculated. The mean breath-to- breathinterval duration was not significantly shorter during 1F than during 2F. SD and SDDSI, however, showed significantly lower values during 1F, demonstrating that the fetal breathingrhythm is more regular during state 1F than during state 2F epochs. Regular fetal breathingis thus a concomitant of state 1F.