Association between Accelerations and Decelerations of Fetal Heart Rate

Abstract

Cardiotocography (CTG) is the most popular test for establishing the fetal health status. Among its characterizing features there are the fetal heart rate (FHR) accelerations (ACC), usually considered a sign of fetal well-being; and decelerations (DEC), some of which may indicate the risk of fetal hypoxia. Thus, ACC and DEC are usually considered independent phenomena possibly providing opposite information on the fetus clinical status. CTG is typically analyzed by visual inspection; still a computerized analysis may provide a more objective CTG interpretation and precise ACC and DEC characterization. Aim of the present study is to propose an automatic procedure for ACC and DEC identification and characterization, and to investigate a potential relationship between their occurrence. The 552 tracings of the Physionet “CTU-CHB intrapartum CTG database” were analyzed according to a procedure that includes: FHR pre-processing; 20 min windowing; baseline estimation; and ACC and DEC identification and characterization. Specifically, ACC and DEC were defined as FHR deviations from baseline of at least 15 bpm for at least 15 s and then characterized in terms of length (s), amplitude (bpm) and area (length.amplitude; bpm.s). Only 383 (69.4%) CTG recordings showed sufficiently good FHR signal quality to be enrolled in the study. Number of DEC per window was significantly higher than ACC (4.0 vs 2.5; P<10^-14). DEC were characterized by a comparable length but high-er amplitude and area than ACC (LNG: 56 s vs 61 s, P=0.2573; AMP: 12 bpm vs 10 bpm, P<10^-11; AREA: 688 s·bpm vs 618 s·bpm, P=0.0032). DEC total area in a 20-min window was higher than that of ACC (3074 s·bpm vs 2007 s·bpm, P<10^-9), but such areas were also strictly correlated (ρ=0.72; P<10^-62). Thus, in a CTG recording, ACC and DEC are not independent phenomena but their occurrence is strictly associated.