Do spectral bands of fetal heart rate variability associate with concomitant fetal scalp pH?

BACKGROUND

Objective information on specific fetal heart rate (FHR) parameters would be advantageous when assessing fetal responses to hypoxia. Small, visually undetectable changes in FHR variability can be quantified by power spectral analysis of FHR variability.

AIMS

To investigate the effect of intrapartum hypoxia and acidemia on spectral powers of FHR variability.

STUDY DESIGN

This is a retrospective observational clinical study with data from an EU multicenter project.

SUBJECTS

We had 462 fetuses with a normal pH-value (pH>7.20; controls) in fetal scalp blood sample (FBS) and 81 fetuses with a low scalp pH-value (≤ 7.20; low-FBS pH-fetuses). The low-FBS pH-fetuses were further divided into two subgroups according to the degree of acidemia: fetuses with FBS pH7.11-7.20 (n = 58) and fetuses with FBS pH ≤7.10 (n = 23).

OUTCOME MEASURES

Spectral powers of FHR variability in relation to the concomitant FBS pH-value.

RESULTS

Fetuses with FBS pH ≤7.20 had increased spectral powers of FHR variability compared with controls (2.49 AU vs. 2.23 AU; p = 0.038). However, the subgroup of most affected fetuses (those with FBS pH ≤7.10) had significantly lower FHR variability spectral powers when compared to fetuses with FBS pH7.11-7.20.

CONCLUSIONS

This study shows that spectral powers of FHR variability change as a fetus becomes hypoxic, and that spectral powers decrease with deepening fetal acidemia.