Complexity-loss in fetal heart rate dynamics during labor as a potential biomarker of acidemia

Background: Continuous fetal heart rate (FHR) monitoring remains central to intrapartum care. However, advances in signal analysis are needed to increase its accuracy in diagnosis of fetal hypoxia. Aims: To determine whether FHR complexity, an index of multiscale variability, is lower among fetuses born with low (<= 7.05) versus higher pH values, and whether this measure can potentially be used to help discriminate the two groups. Study design: Evaluation of a pre-existing database of sequentially acquired intrapartum FHR signals. Subjects: FHR tracings, obtained from a continuous scalp electrocardiogram during labor, were analyzed using the multiscale entropy (MSE) method in 148 singletons divided in two groups according to umbilical artery pH at birth: 141 fetuses with pH > 7.05 and 7 with pH <= 7.05. A complexity index derived from MSE analysis was calculated for each recording. Results: The complexity of FHR signals for the last two hours before delivery was significantly (p < 0.004) higher for non-acidemic than for acidemic fetuses. The difference between the two groups remained significant (p < 0.003) when FHR data from the last 30 min before delivery were excluded. Conclusion: Complexity of FHR signals, as measured by the MSE method, was significantly lower for acidemic than non-acidemic fetuses. These results are consistent with previous studies showing that decreased nonlinear complexity is a dynamical signature of disrupted physiologic control systems. This analytic approach may have discriminative value in FHR analysis. (C) 2013 Elsevier Ireland Ltd. All rights reserved.