What causes early decelerations in fetal heart rate?

Early decelerations in fetal heart rate are primarily caused by head compression during labor. This occurs when the fetal head exerts pressure on the cervix or other structures in the birth canal, triggering a vagal response. As a result, there is a transient decrease in heart rate that coincides with uterine contractions. Early decelerations are characterized by their gradual decrease and return to baseline heart rate, mirroring the timing of contractions.

This physiological response is typically considered a benign finding in the context of labor, indicating that the fetus is responding appropriately to the stress of contractions. Such decelerations are often viewed as a sign of fetal well-being, especially when accompanied by a reassuring baseline heart rate and variability.

Other potential causes listed do not specifically lead to early decelerations as seen in head compression. Cord compression can lead to variable decelerations that are sharp and abrupt, while lung hypoplasia and chronic hypoxemia typically present differently and may be associated with other forms of fetal distress.