Inpatient Obstetric Nurse (NCC) Practice Exam

In a reactive non-stress test (NST) for a preterm fetus, accelerations must last a minimum of 10 seconds. This duration is crucial as it indicates that the fetus's heart rate accelerates appropriately in response to fetal movement or stimulation, which reflects adequate fetal oxygenation and an intact central nervous system.

The 10-second criterion is established based on fetal physiology, where accelerations signify healthy autonomic responses and can help clinicians assess the well-being of the fetus. A longer acceleration duration such as 15 or 20 seconds provides additional reassurance but is not necessary to meet the reactive criteria for preterm fetuses. A duration of 5 seconds is considered too short and does not sufficiently demonstrate the fetus's response to stimuli.