Estimation of long-term correlations from Fetal Heart Rate variability signal for the identification of pathological fetuses

A crucial problem in fetal monitoring is the correct interpretation of biophysical measurements. An important question is therefore how to decide if fetal small dimensions are physiological or due to a pathological condition, such as intrauterine growth restriction (IUGR), a metabolic dysfunction which does not allow the fetus to achieve its genetically predetermined size. This study proposes to estimate the long-term correlations of the fetal heart rate variability signal. The method adopted was the detrended fluctuation analysis and its variants. Two scaling slopes were considered: a short-term scaling slope v₁ (n <76, 38 s) and a long-term scaling slope v₂ (n >76, 38 s). This last index was able to identify the severe IUGRs and to separate them from both not severe IUGRs and normal fetuses, which instead present similar values. The crossover seems to be an intrinsic characteristic of the FHRV signal.