Studies on cross correlation coefficient of fetal heart rate and fetal movement signals detected by ultrasonic Doppler fetal actocardiograph

Cross correlation coefficients of fetal heart rate (FHR) and fetal movement (FM) signals detected by ultrasonic Doppler actocardiograph were studies. Actocardiographic output was stored in a floppy disk through an AD converter. The parameters for every 5 minute period were calculated in 461 periods for 68 normal pregnant women at 14 to 41 weeks of gestation. 1) Between FHR acceleration (ACC) and the maximum coefficient, the averages for the maximum coefficients in 5 minute periods without and with ACC were 0.141 and 0.275, respectively. The respective lag time averages were 13.1 and 7.6 seconds. These results may indicate that the FHR ACC temporarily follow FM with a time lag of several seconds in the active state. 2) The largest value for the maximum coefficients and the lag times in each examination were investigated according for each gestational week. The coefficients increased and the lag times decreased as gestation advanced. 3) The coefficients in the periods showing typical fetal breathing movement and fetal hiccups were very small. Periodic fetal suckling observed with real-time B mode showed large coefficient with a 3 sec' delay in FM.