What typically causes early decelerations in fetal heart rate?

Early decelerations in fetal heart rate are typically caused by head compression. This phenomenon is related to the mechanical impact of the fetal head against the cervix or pelvic wall during labor. When the head compresses against the cervix, it stimulates the vagus nerve, leading to a transient decrease in heart rate that mirrors uterine contractions. This deceleration begins with the contraction and returns to baseline as the contraction ends, which makes it distinct from other types of decelerations, such as variable decelerations associated with cord compression.

While other factors may affect fetal heart rate, they do not typically produce the same pattern associated with early decelerations. For instance, cord compression leads to variable decelerations that are often abrupt and not time-locked with contractions. Fundal pressure does not directly cause early decelerations as it pertains more to the application of pressure on the abdomen rather than compressing the fetal head. Maternal fever could influence fetal heart rate due to increased metabolic demand but is not a direct cause of early decelerations. Understanding the mechanism behind early decelerations emphasizes the significance of fetal head positioning and labor progression in fetal heart monitoring.