Time series analysis of human foetal breathing activity at 30-39 weeks gestation

Thirty-one healthy human fetuses were each observed with a real-time scanner continuously for 24 h. The percentage of time spent breathing was computed for each 5 min observation period during the 24 h which produced a time series of 288 observations for each fetus. Box-Jenkins modelling techniques and analysis of frequency spectrum distribution were used to quantify mathematically the human fetal breathing data. The data was described mathematically by a first-order auto-regression z(t)=0.7 z(t-1) + epsilon(t) which confirmed and quantified the episodic nature of foetal breathing activity. Evaluation of the spectral distribution of the fetal breathing movements identified a significant band of pseudo-periodic components with repeat periods ranging from 100 to 500 min (P less than 0.001). Results of this study indicated that the occurrence of fetal breathing movements were non-random and that Box-Jenkins modelling results and spectral power distribution may be useful in identification and description of any fetal breathing patterns which differ from normal patterns.