Fetal Heart Rate Fragmentation

Abstract

Intrapartum fetal monitoring's primary goal is to avoid adverse perinatal outcomes related to hypoxia/acidosis without increasing unnecessary interventions. Recently, a set of indices were proposed as new biomarkers to analyze heart rate (HR), termed HR fragmentation (HRF). In this work, the HRF indices were applied to intrapartum fetal heart rate (FHR) traces to evaluate fetal acidemia. The fragmentation method produces four indices: PIP-Percentage of inflection points; IALS-Inverse of the average length of acceleration/deceleration segments; PSS-Percentage of short segments; PAS-Percentage of alternating segments. On the other hand, the symbolic approach studied the existence of different patterns of length four. We applied the measures to 246 selected FHR recordings sampled at 4 and 2 Hz, where 39 presented umbilical artery's pH ≤ 7.15. When applied to the 4 Hz FHR, the PIP, IASL, and PSS showed significantly higher values in the traces from acidemic fetuses. In comparison, the percentage of "words" $W_1^h$ and $W_2^s$ showed lower values for those traces. Furthermore, when using the 2 Hz, only IASL, W ₀, and $W_2^m$ achieved significant differences between traces from both acidemic and normal fetuses. Notwithstanding, the ideal sampling frequency is yet to be established. The fragmentation indices correlated with Sisporto variability measures, especially short-term variability. Accordingly, the fragmentation indices seem to be able to detect pathological patterns in FHR tracings. These indices have the advantage of being suitable and straightforward to apply in real-time analysis. Future studies should combine these indexes with others used successfully to detect fetal hypoxia, improving the power of discrimination in a larger dataset.

Keywords: acidemia; fetal heart rate; fragmentation; short-term variability; symbolic dynamics; umbilical cord pH.

Figure 1

(A) Representation of 50 s of a fetal heart rate time series sampled at 2 Hz. The trace presents 53 inflection points (*) and there are 33 segments between inflections points that are accelerations or decelerations. $PIP=\frac{53}{101}\approx 53\%$; $PIP\mathit{\text{hard}}=\frac{11}{101}\approx 11\%$; $PIP\mathit{\text{soft}}=\frac{42}{101}\approx 42\%$; IALS≈66%; PSS≈82%; PAS = 0. (B) Representation of 25 s of a fetal heart rate time series sampled at 4 Hz with the classification of eight words as an example.