Specific change in spectral power of fetal heart rate variability related to fetal acidemia during labor: Comparison between preterm and term fetuses

Background: Spectral analysis of fetal heart rate (FHR) variability is a useful method to assess fetal condition. There have been several studies involving the change in spectral power related to fetal acidemia, but the results have been inconsistent. Aims: To determine the change in spectral power related to fetal umbilical arterial pH at birth, dividing cases into preterm (31-36. weeks) and term (≥ 37. weeks) gestations. Study design: Case-control study. The 514 cases of deliveries were divided into a low-pH group (an umbilical arterial pH < 7.2) and a control group (pH ≥ 7.2). Subjects: FHR recorded on cardiotocography during the last 2. h of labor. Outcome measures: The spectral powers in various bands of FHR variability. Results: In preterm fetuses, the total, low (LF), and movement (MF) frequency spectral powers and LF/HF ratio were significantly lower in the low-pH group than the control group (all P< 0.05). In contrast, in term fetuses, the total frequency, LF, and MF powers were significantly higher in the low-pH group than the control group (all P< 0.05). The area under the receiver operating characteristic of LF power to detect a low pH at birth was 0.794 in preterm fetuses and 0.595 in term fetuses. The specificity was 86.8% and 93.3% in preterm and term fetuses, respectively. Conclusions: The changes in spectral power responding to a low pH are different between term and preterm fetuses. Spectral analysis of FHR variability may be useful fetal monitoring for early detection of fetal acidemia.