Increased Fetal Activity and Heart Rate During and Immediately After Pulsed Doppler Echocardiography

Introduction: Previous reports have suggested that the use of continuous‐wave Doppler for nonimaging heart rate monitoring or in utero Doppler imaging increased fetal activity. In this study, 11 fetuses (EGA 20–28 weeks) underwent a cardiac 2‐D ultrasound and pulsed Doppler examination (since pulsed Doppler is more often used for fetal cardiac diagnosis) with 2‐D and Doppler performed in a randomized order and with 10‐minute ultrasound observation periods with as little transducer movement as possible before, during, and after 2‐D only, and Doppler evaluation. Methods: All studies were performed with informed consent at the lowest available Doppler power < 90 mW/cm² spatial peak temporal average. Fetal heart rate, the number of fetal gross movements / min, and the percent time occupied by fetal movements were evaluated by two blinded observers from video taped records. Patients had been referred to rule out fetal heart disorders but all echoes showed normal cardiac anatomy. Results: Fetal heart rate after pulsed Doppler study was statistically higher by analysis of variance (mean 127 beats/min) than in the pre‐Doppler evaluation period (mean 120) and was highest during the Doppler exam period (mean 136; P < 0.05) in 10 of 11 fetuses. The percent time of fetal movements was highest during the Doppler exam period and in 9 of 11 fetuses movement increased. The raw number of gross movements / min, however, was highest after the Doppler. No such changes occurred during or after 2‐D alone. Conclusion: Whether associated with slightly higher energy output, minimal thermal changes, or audible switching or electronic output sounds transmitted from the instrumentation through the uterus, fetal heart rate and activity increased in our study both during and after pulsed Doppler examination.