Fetal heart rate variability (fluctuation) is a positive finding indicating fetal well-being and is evaluated as a 'reactive NST'. In some cases, when the baby is in a sleep state or its activity is reduced, the expected criteria in the NST test (e.g., significant accelerations in heart rate) may not be observed. This condition is referred to as 'non-reactive NST'. Typically, a sleeping baby can be made reactive by activating it with external sounds or gentle stimuli, and the NST results return to normal. However, if there is an underlying medical problem affecting the fetus's health or threatening its vitality, the NST may not become reactive, and further examination and evaluation become necessary.