Late decelerations in fetal heart rate are primarily caused by what physiological response?

Late decelerations in fetal heart rate are primarily associated with uteroplacental insufficiency, which leads to a decrease in oxygen transfer to the fetus, resulting in a hypoxic state. The physiological response underlying late decelerations is primarily the activation of chemoreceptors in the fetus that detect low partial pressure of oxygen (paO2). As the fetus experiences decreased oxygen supply, the heart rate typically reflects a deceleration in response to those low oxygen levels, indicating that the fetal autonomic nervous system is reacting to an impaired environment.

This mechanism signifies that the fetus is subject to stress due to inadequate blood flow or oxygenation, and what is observed as late decelerations is essentially a late response related to uteroplacental blood flow, not an immediate or direct effect such as those from uterine activity or maternal hypotension. Understanding the underlying factors affecting the fetal heart rate pattern is critical in obstetric care, as recognizing late decelerations can indicate a potential need for intervention to ensure fetal well-being.