[Fetal heart rate variation in magnetocardiography and cardiotocography--a direct comparison of the two methods]

Heart rate variability (HRV) is becoming increasingly important in the analysis of prepartal cardiotocography (CTG). Dawes and Redmann have developed a computer algorithm which can calculate short-term variability on the basis of CTG data. In dealing with artefacts, CTG monitors average heart rate values over several beats which makes the use of standard measures of HRV such as the root mean square of successive differences (RMSSD) inappropriate. Fetal magnetocardiography (FMCG) enables the registration of signals similar to the electrocardiogram and this permits the precise determination of heart beat duration and, in consequence, of measures of fetal HRV.

In this study we applied both methods--CTG and FMCG--sequentially and simultaneously in healthy pregnancies. Fetal short-term HRV was estimated on the basis of RMSSD values for both methods.

The RMSSD values of the FMCG data were generally higher and showed a wider dynamic range than those of the CTG. The direct comparison of the simultaneously acquired data demonstrated that the data processing of the CTG signal leads to a suppression of essential aspects of short-term HRV.

FMCG permits a substantially more differentiated examination of fetal HRV and offers new possibilities in the analysis of fetal cardiac activity.