What does an NST primarily evaluate in fetal monitoring?

The non-stress test (NST) primarily evaluates the fetal heart rate response to fetal movement. This test is designed to provide insight into the wellbeing of the fetus by analyzing how the heart rate accelerates in response to movements, which is a sign of a healthy, functioning autonomic nervous system. An adequate response indicates that the fetus is receiving sufficient oxygen and is not in a state of distress.

During the NST, the healthcare provider typically uses an electronic fetal monitor to assess heart rate patterns in relation to recorded movements of the fetus. A reactive NST, which is defined by the presence of two or more accelerations of at least 15 beats per minute above the baseline heart rate in a 20-minute period, signifies that the fetus is likely healthy and thriving.

This focus on heart rate responses specifically distinguishes the NST from other tests, which might assess different aspects of fetal wellbeing or maternal health, such as the relationship between contractions and fetal heart rate patterns or maternal vital signs during labor.