Antepartal analysis of fetal heart rate variability by abdominal electrocardiography.

The success rate of some methodological factors influencing the antepartal analysis of fetal heart rate variability (FHRV) by abdominal electrocardiography (aFECG) were studied in 80 normal and 554 high risk pregnancies. The success rate of FHRV analysis was found to be dependent on the gestational age with virtually 100% success at 22 to 25 weeks and at 40 to 41 weeks of gestation. The lowest rate of success, 50% was found around the 30th week of gestation (Fig. 1). The fifteen-degree lateral tilt and the supine position of the mother were found to be equal respecting the success rate and the test results, while the 90-degree lateral tilt was found to be less favorable for the analysis. FHRV analysis succeeded more often with electrode paste than it did with tap water moistening or with dry electrodes. The rejection limit of maximum interval differences in FHRV analysis was found to be an important factor influencing the test results. The variability indices should be compared only if they have been measured with the same rejection logic. Differential index, of short-term variability, can be measured from short samples of aFECG, having a good correlation between DIs measured using 1-minute, 5-minute and 20-minute samples (Figs. 3, 4). On the other hand, interval index measuring the long-term variability should be measured using longer samples of aFECG.