Alterations in irregular and fractal heart rate behavior in growth restricted fetuses

OBJECTIVES: To determine whether irregularity, and short- and long-term fractal correlation reflecting smoothness of heart rate behavior are changed in intrauterine growth restricted fetuses. STUDY DESIGN: Fetal heart rate data of 192 normal fetuses and 86 intrauterine growth restricted fetuses between 31 and 42 weeks of gestation were studied. Approximate entropy to quantify irregularity, and short-term (< or =80 beats, alpha1) and long-term (>80 beats, alpha2) fractal scaling exponents to quantify the short- and long-term fractal correlation were calculated. RESULTS: In the intrauterine growth restricted fetuses, the approximate entropy was significantly lower (P<0.001). The alpha2 value was significantly higher (P=0.0001) than in the normal fetuses, which performed better (F=34.2, P<0.0001) than other heart rate variability indexes in differentiating the intrauterine growth restricted fetuses from the normal fetuses in stepwise discriminant analysis. CONCLUSIONS: Compared to normal fetuses, intrauterine growth restricted fetuses show a difference in that the irregularity of the fetal heart is decreased. A more apparent difference is that the long-term fractal correlation of the fetal heart is increased and the fetal heart is smoother in the long-term scale.