The effect of chart speed on fetal monitor interpretation

Objective: Electronic fetal heart monitor chart speeds vary between countries, and it is unclear whether differing chart speeds affect physician tracing interpretation. Methods: Twenty-minute segments of 19 tracings were displayed on both 1 and 3 cm/min strips and interpreted by 14 physicians at the particular speed they were accustomed to reading. Interpretations of tracing characteristics were compared between groups using free margin kappa, a measure of interobserver agreement. Results: Compared to 3 cm/min tracings, 1 cm/min tracings were significantly more often identified as having absent than minimal variability, and minimal than moderate variability. Accelerations were significantly more often identified in 1 versus 3 cm/min strips. There were no significant differences between groups with respect to baseline fetal heart rate, prolonged or repetitive decelerations, or American College of Obstetricians and Gynecologists tracing category. Neither chart speed had substantial interobserver agreement in tracing variables; however, agreement was consistently higher in 3 versus 1 cm/min tracings (all p < 0.05). Conclusions: Tracing interpretation is significantly affected by fetal monitor chart speed with regards to variability, acceleration and deceleration. Further studies are required to determine if differences in chart speed interpretation affect clinical management.