Quantitative and qualitative relationships between fetal heart rate accelerations and fetal movement

We measured duration, amplitude, and duration at peak amplitude of 117 heart rate accelerations of 12 normal fetuses greater than 36 weeks gestation. Fetal movement measured by Doppler was analyzed for duration of movement; number of limb, spine, and rolling movements; and total movements per epoch of movement. Of 117 accelerations, only five were not associated with recorded movement and all of these had amplitude less than 12 bpm and duration less than 16 seconds. Only four (3% accelerations occurred before fetal movement was detected, 23 (20% began after onset of movement, and the large majority (77% of fetal heart rate (FHR) accelerations occurred synchronously with fetal movement. In addition to an obvious correlation between number of movements and time spent in movement, a relationship exists between movements and duration of accelerations. Movements do not correlate with amplitude of accelerations. Fetal movement and heart rate acceleration relate temporally, but the strength or type of movements does not affect the amplitude of accelerations. This supports the argument that FHR accelerations are not directly mediated by quantity or quality of fetal movement, but that either all or none of the responses or central mechanisms are involved.