At what gestational age is the NST typically performed?

• A. 20 weeks
• B. 28 weeks
• C. 32 weeks
• D. ≥ 32 weeks

Answer: (D)

Non-stress testing checks fetal well-being by monitoring the fetal heart rate as the fetus moves. It’s most informative when the fetus’s autonomic nervous system and oxygenation are mature enough to produce reliable heart-rate accelerations in response to activity. Early in pregnancy, the fetus’ regulatory systems aren’t consistently developed, so accelerations can be absent even in healthy fetuses, making the test less reliable. For that reason, NST is typically performed in the late third trimester, when the fetus is mature enough to show predictable heart-rate responses. A reactive NST is defined by two accelerations within about a 20-minute period, indicating adequate oxygenation and reserve.