V-shaped deceleration differs in the pattern of carotid blood flow from variable deceleration provoked by cord compression

Objective: To investigate whether V-shaped decelerations in fetal heart rate tracing are a physiologic response to fetal movements or secondary to cord compression. Study design: Six pregnant sheep and their fetuses (115-125 days of gestation) were surgically instrumented and studied. Fetal electrocardiogram, carotid blood flow, arterial blood pressure and fetal movement were continuously monitored for 24 hours. Following the undisturbed 24 hour recording, these parameters were monitored during umbilical cord compression (n = 6). Differences in these parameters between V-shaped decelerations and decelerations provoked by cord compressions were examined. Results: Elevation of blood pressure and decreased carotid blood flow were observed coincidentally with the initiation of V-shaped decelerations. In cord compression, elevation of both blood pressure and carotid blood flow were followed by a decreased heart rate. V-shaped decelerations exhibited a different alteration of carotid blood flow compared to decelerations caused by umbilical cord compression. Conclusion: V-shaped deceleration is a physiologic response secondary mainly to fetal movements and is not caused by cord compression.