Large fetal heart rate decelerations at term associated with changes in fetal heart rate variation

Objective: The objective was to determine whether large antepartum decelerations in fetal heart rate were associated with a switch from high to low fetal heart rate variation, suggestive of a change in sleep state, and whether the variation predicted outcome. Study Design: Retrospective computerized analysis of 10,272 cardiotocographic records from 3998 patients at 37 to 42 weeks' gestation from four centers in England and Italy identified 140 good-quality records with large decelerations (more than 20 lost beats in area). Results: In otherwise normal cardiotocograms a large deceleration had a 40% chance of association with a downward change in fetal heart rate variation (69% when the deceleration exceeded 100 lost beats). The change resembled that occurring naturally with behavioral states. Uterine contractions did not always precede large decelerations. When they did, the lag time (peak of contraction — trough of deceleration) increased from 28 seconds (at 20 to 29 lost beats) to > 100 seconds with increase in deceleration area. Of patients with large decelerations 76% had a normal vaginal delivery. Conclusion: Large decelerations near term, present in up to 5% of patients with otherwise normal fetal heart rate and variation, are often associated with a fall in fetal heart rate variation characteristic of a change in sleep state, without ominous significance.