Approximate Entropy: Analysis of Fetal Heart Rate Variability in Normal and Growth Retarded Fetuses

Hwang, Jung Hye; Park, Moon Il; Yum, Myung Kul

Abstract

OBJECTIVES
This study is aimed to quantify the complex dynamics of beat-to-beat fetal heart rate(FHR) fluctuations by using approximate entropy(ApEn) which is a recently developed mathematical formula quantifying regularity and also to determine the differences between normal fetuses and growth retarded fetuses. BACKGROUND: Recently, some measures of heart rate variability and nonlinear "complexity" of heart rate dynamics have been used as indicators fetal well-being. Approximate entropy is a new mathematical approach and formula to quantify regularity in data. It has been shown to provide new information in fetal heart rate analysis. Because growth retarded fetus accounts for a significant increase in perinatal morbidity and mortality, than normal fetus, we postulated that there existed important differences between normal fetuses and growth retarded fetuses.
METHODS
We analyzed FHR tracings for 40 minutes, and approximately 5,000 points in normal fetuses(n=315) and growth retarded fetuses(n=76). The overall "complexity" of each FHR time series was quantified by its approximate entropy, measure of regularity derived from nonlinear dynamics, "chaos theory".
RESULTS
Mean baseline FHR increased in growth retarded fetuses than normal fetuses. And the FHR ApEn significantly decreased in growth retarded fetuses(ApEn=0.623) compared to that of the normal fetuses(ApEn=0.868) throughout all gestational ages(p < 0.001).
CONCLUSIONS
The ApEn of FHR decreased in growth retarded fetuses throughout all gestational ages. These findings indicated that decreased ApEn values of FHR are associated with sickness and the greater perinatal morbidity risks. Therefore ApEn quantifies subtle changes in FHR regularity and promises for new information in FHR analysis.