AN ESTIMATE OF FETAL AUTONOMIC STATE BY SPECTRAL-ANALYSIS OF FETAL HEART-RATE FLUCTUATIONS

The assessment of the functional state of the autonomic nervous system (ANS) in real time, by means of spectral analysis of fetal heart rate variability, may serve to improve the diagnosis of pathologic conditi ons of importance to the perinatologist. The combination of two approa ches, namely an efficient method for detecting fetal ECG from the abdo minal maternal signal, followed by spectral analysis of heart rate var iability, is tested as a new noninvasive tool to assess fetal viabilit y in real time. This study demonstrates a pattern of ANS development v ia the spectral contents of heart rate variability. It is shown that d uring ''quiet state,'' the ''young'' fetuses (gestational age = 23.5 /- 1 wk) present twice as much power of heart rate fluctuations at all frequencies from 0.2 to 1.0 Hz as ''mature'' fetuses (gestational age = 39.75 +/- 1.5 wk). This finding is coherent with the evolution of a stable and mature ANS activity. At frequencies below 0.1 Hz, a 1/f(al pha) power law relationship (alpha = 0.85, r2 > 0.9) between spectral density and frequency is displayed in the two age groups. A respirator y peak has been observed in some of the short (64-s) traces we analyze d. However, no respiratory peak was ever observed in a long (256-s) tr ace, due to the episodic nature of the fetal breathing and immaturity of the ANS.