PAOLONE, A. M., M. SHANGOLD, D. PAUL, J. MINNITTI, and S. WEINER. Fetal heart rate measurement during maternal exercise—avoidance of artifact.Med. Sci. Sports Exerc., Vol. 19, No. 6, pp. 605–609, 1987. The purpose of this study was to investigate the possibility that motion artifact may override the recording of fetal heart rate (FHR) with Doppler ultrasound fetal monitors during maternal exercise on cycle ergometers and treadmills, and to test the efficacy of two-dimensional ultrasound directed M-mode echocardiographs for determining FHR during maternal treadmill exercise. Four pregnant women (26 to 30 yr, X = 28, gestational age = 28 to 34 wk) pedaled a cycle ergometer at 25 to 50 W, while a second group (N= 4) (24 to 36 yr, X = 29, gestational age = 30 to 37 wk) walked on a treadmill at either 1.5 or 2.0 mph. Fetal monitor recordings (Hewlett-Packard 8040A) were consistent with pedal rate in the range of 50 to 70 rpm and with stepping rate in the range of 70 to 76 steps per min at 1.5 mph and 100 to 106 steps per min at 2.0 mph on the treadmill. Actual mean FHRs (audible signal from fetal monitor) were in the normal range [150.5 ± 10.25 bpm (cycle ergometer) and 148.8 ± 2.3 bpm (treadmill)]. In a separate session, the cycle ergometer group walked on a treadmill at a maternal heart rate of 140 bpm while FHR was determined by two-dimensional ultrasound directed M-mode echocardiographs. Off-line analysis of fetal cardiac cycle time (clinical graphics analyzer) allowed accurate FHR measurements which were not confounded by motion artifact. Mean FHR during maternal treadmill exercise (158.0 ± 12.0 bpm) was not different (P > 0.05) when compared to pre-exercise standing (140 ± 3.6) and also during the post-exercise period (sitting) (151 ± 6.5) compared to the sitting pre-exercise measurements (147 ± 8.2). It was concluded that M-mode echocardiographs of fetal cardiac activity during maternal exercise provide artifact-free determinations of FHR and that the apparent fetal bradycardia during maternal exercise reported by other investigators is most likely motion artifact.