The Fetal Non-Stress test is a simple, non-invasive test performed in pregnancies over 28 weeks gestation.The test is named ânon-stressâ because no stress is placed on the fetus during the test. nonreactive non-stress result requires additional testing to determine whether the result is truly due to poor oxygenation, or whether there are other reasons for fetal non-reactivity (i.e. sleep patterns, certain maternal prescription or nonprescription drugs).