The significance of amplitude and duration of fetal heart rate acceleration in non-stress test analysis

Abstract

Objective: This study was conducted to assess the relative significance of the amplitude versus the duration of accelerations in non-stress test (NST) analysis.

Materials and methods: A total of 3055 normal fetal heart rate (FHR) tracings at 30-42 weeks' gestation were analyzed by automated FHR analyzing software. Accelerations were classified as one of four combinations of amplitude and duration: 15 bpm-15 seconds (Acc15-15), 15 bpm-10 seconds (Acc15-10), 10 bpm-15 seconds (Acc10-15) and 10 bpm-10 seconds (Acc10-10). We estimated the correlation among the FHR acceleration combinations using correlation analysis based on linear regression models.

Results: Linear regression models demonstrated statistically significant linear associations between Acc15-15 and Acc15-10 (r(2) = 0.998, p < 0.0001) and between Acc10-10 and Acc10-15 (r(2) = 0.989, p < 0.0001). There was significant association based on amplitude and relatively low correlation based on duration (Pearson correlation coefficient = 0.99 between Acc10-10 and Acc10-15, and 0.99 between Acc15-15 and Acc15-10). In the relationships of the FHR-work values, amplitude was a more important component of FHR acceleration than duration [Acc10-10 (1.67 beat) < Acc10-15 (2.50 beats) = Acc15-10 (2.50 beats) < Acc15-15 (3.75 beats)].

Conclusion: Amplitude was a more significant component of FHR acceleration than duration in the computerized analysis of NST.