Quantifying Phase Coupling between Fetal Heart Rate and Uterine Contractions

Fetal heart rate (FHR) and uterine contractions (UC) are routinely monitored during labor using cardiotocogra-phy (CTG). Clinical interpretation of CTG signals often assesses signal coupling patterns to determine fetal responses to uterine contractions. However, their effectiveness is sometimes limited by low-quality recordings. Traditionally, CTG quality is assessed based on signal loss percentage, overlooking the possibility that non-zero signals may still be non-physiological. This study aims to investigate the coupling relationship between non-zero FHR and UC signals and determine its potential as an index for CTG quality assessment. Using a dataset of 271 CTG recordings without signal discontinuities and surrogate data generated through random shuffling, we quantified the association between FHR and UC using the phase coupling index (λ). Our results show that λ values are significantly different before and after data surrogation, confirming that they quantify a meaningful temporal relationship between FHR and UC. Furthermore, we examined the correlation between λ and four established FHR features and found significant associations with the average depth of decelerations (MAD_dtrd) and variability (Hurst parameter, H) in both univariate and multivariate analysis. These findings suggest that λ may capture temporal and physiological dynamics between FHR and UC signals and could serve as a potential quality metric for non-zero CTG data.Clinical Relevance-Phase coupling index of FHR and UC may serve as a metric for identifying quality CTG signals, potentially aiding in visual and computerized analysis.