The evaluation and significance of intrapartum FHR-oscillation patterns

The last two hours of 342 intrapartum FHR records of high technical quality were evaluated visually with simple tools (compasses, caliper). All data were entered on punched cards (25 pro fetus) and analyzed using an IBM system 370/135. In 253 fetuses with an actual pH in the umbilical artery (UA) above 7.199 the oscillation frequency (OF) during the last 30 min. preceding delivery amounted to 9.5 +/- 4.5 (4615 minutes without decelerations or accelerations). The 5th percentile, the median and the 95th percentile were 2,9 and 18 per minute respectively. OF refers to the number of visually detectable turning points in baseline FHR. There exists a significant association (2 alpha less than 0.001) between the OF and the oscillation amplitude (OA) per minute: a reduction in OF is followed by a decrease in OA even in vigorous infants. In acidotic fetuses OF is decreased when compared with FHR minutes of equal OA in nonacidotic infants. However this becomes statistically significant only in fetuses with actual pH (UA) below 7.150 i.e. in fetuses with severe acidosis. These findings can explain why the loss of FHR variability as a single symptom may be misleading in individual cases.