What characterizes variable decelerations in fetal heart rate (FHR)?

Variable decelerations in fetal heart rate (FHR) are characterized by their abrupt nature. These decelerations typically occur in a sudden drop in fetal heart rate that can begin and end quickly, often within a span of less than 30 seconds. This abrupt change is typically caused by umbilical cord compression, where the cord gets pinched or compressed during contractions or movement, leading to transient reductions in blood flow and oxygen to the fetus.

The other choices highlight different patterns or durations of decelerations that do not apply to variable decelerations. For instance, a gradual decrease in heart rate over time is more representative of late decelerations, while consistent occurrence throughout labor may pertain to varying patterns depending on the other circumstances surrounding labor. Additionally, the fact that decelerations can last more than 10 seconds is crucial in differentiating among types of FHR decelerations and understanding their clinical significance. Hence, the abrupt nature is key to identifying variable decelerations correctly.