[Studies on periodic changes of fetal and neonatal heart rate]

The changes in fetal heart rate (FHR) and neonatal heart rate (NHR) were analyzed by the functions of autocorrelation and cross correlation between FHR (or NHR) and digitally generated sine waves with the use of a 2100A minicomputer in 201 fetuses which received FHR records 221 times and 11 neonates. Among these cases, 9 fetuses and 1 neonate showed some periodicities in FHR (or NHR) long term variability obtained from gross examination as well as from the calculation of the functions. Fetal cases showed the 1st maximum at 13 to 22 seconds after autocorrelation analysis and the neonate case at 25 seconds. In cross correlation analyses of fetal cases, peaks were noted at 2.72 to 4.48cpm in the frequency distribution. In the neonate case, a peak was noted at 2.5cpm. The fetuses showed changes in their inactive stage that were determined by decreased fetal movement. No particular prognosis was noted among these fetuses after discovering periodic FHR changes. The neonate showed a change in hypoxia. This neonate died 2 days after the examination. In conclusion, about 3 to 5 cpm periodic changes may occur in inactive stages of normal fetus.