What can cause variable decelerations in fetal heart rate?

Variable decelerations in fetal heart rate typically occur due to umbilical cord compression. When the umbilical cord is compressed, there is a transient reduction in blood flow and oxygen delivery to the fetal heart, leading to a drop in the heart rate. This type of deceleration is characterized by its abrupt onset and recovery, often correlating with uterine contractions.

In the context of your answer, while head compression can also create decelerations, they are usually considered more predictable and are categorized as early decelerations. Oligohydramnios, defined as a lower-than-normal amount of amniotic fluid, can increase the likelihood of cord compression, but it is not a direct cause of variable decelerations in the same way that cord compression is. Infection can lead to variations in fetal heart rate, but it is generally associated with more systemic fetal distress rather than the characteristic pattern of variable decelerations. Thus, cord compression stands out as the primary and direct cause linking to the pattern observed in variable decelerations.