What does a non-stress test (NST) primarily evaluate?

A non-stress test (NST) primarily evaluates the fetal heart rate response to movement, which is critical in assessing fetal well-being, particularly in the third trimester of pregnancy. During this test, the fetal heart rate is monitored over a specific period, typically 20 to 40 minutes, to identify how it reacts when the fetus moves. An increase in fetal heart rate, known as heart rate acceleration, is considered a reassuring sign, indicating that the fetus is getting enough oxygen and is healthy.

This test is especially valuable in monitoring pregnancies that may be at risk due to various conditions, such as gestational diabetes, hypertension, or previous stillbirths. A reactive NST, characterized by adequate accelerations associated with fetal movement, usually suggests that the fetus is doing well, while a non-reactive NST might indicate a need for further evaluation or intervention.

In contrast, evaluating maternal vital signs during labor is essential for assessing the mother's health but does not provide specific information about the fetus. Monitoring prenatal vitamin levels in the mother focuses on maternal nutrition rather than fetal status, and assessing pelvic measurements pertains to labor and delivery but not fetal well-being. Thus, the core function of an NST is to monitor and evaluate the fetal heart rate in relation to the fetus