The influence of indirect Doppler ultrasound method on fetal heart rate variability measurement

Fetal heart rate (FHR) signal can be obtained directly from the scalp electrode or indirectly via a Doppler ultrasound transducer. In the first method, we measure a distance between successive R peaks in fetal electrocardiogram. In the noninvasive and more popular indirect method, the Doppler effect is used, which occurs at reflection of ultrasound wave from moving parts of fetal heart; therefore, mechanical signal of heart activity is obtained. Short-term (STV) and long-term (LTV) variability indices are used to express FHR variability. The LabView based application for simultaneous acquisition of direct and indirect FHR signals has been developed to assess the influence of Doppler method errors on indices values. The result was that the LTV indices showed no statistically significant differences, whereas STV indices of Doppler derived FHR were significantly greater than measured directly.