Interval index: a measure of fetal heart rate accelerations

Interval index (II) is a product of statistical analysis of fetal heart intervals measured from fetal electrocardiography and it describes the long term variability. II and three visual parameters of fetal heart rate (FHR) accelerations: the number of accelerations, the heights of maximal acceleration and the sum of accelerations in 40 five-minute samples of abdominal fetal electrography were compared to find out whether II could be used as an automated objective measure of FHR accelerations (r = 0.85), but the correlation was highly significant also with the maximal acceleration and the number of ac-FHR had a poor correlation with accelerations.