Short term variability of fetal heart rate during pregnancies complicated by hypertension

The clinical significance of the differential index (DI), which describes the short term variability of fetal heart rate (FHR), in fetal surveillance was assessed in 202 hypertensive pregnancies. The analyses of FHR variability were made by a microprocessor-based on-line method using the abdominal fetal electrocardiogram as a triggering signal. The analysis was successful in 258 out of 323 trials (80%). Five perinatal deaths (2.5%) occurred in the whole series. Fetal distress developed in 47 out of 137 patients who had a successful FHR analysis within 1 week of delivery. The sensitivity of the antepartum DI in predicting fetal distress in labour was 46%, predictive value was 88% and specificity 97%. The risk of intrapartum fetal distress after a pathological DI was 4 times that after a normal DI (relative risk), which is highly significant.