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Nonstress Test: Evidence-Based Use in High-Risk Pregnancy

For three decades, the nonstress test (NST) has been accepted as a primary fetal surveillance tool for pregnancies at risk for intrauterine death. Subsequently, the NST has been used in combination with ultrasound observations of fetal activity and amniotic fluid volume as the biophysical profile. More recently, this test has been modified by the addition of vibroacoustic stimulation (VAS) or by Doppler recordings of fetal movement (actocardiotocography [ACTG]). The NST’s popularity stems from its ease of application in ambulatory settings, modest technical requirements, and lack of contraindications. Extensive clinical experience has been reported on use of the NST; however, the bulk of the evidence supporting its role in antepartum management is based on level II-3 evidence (multiple time series) rather than level I evidence (randomized controlled trials). In spite of this caveat, the incorporation of the NST into high-risk antepartum protocols has been associated with an apparent reduction in intrauterine fetal death. This monograph will address the biologic basis of the NST in antepartum assessment, its application and interpretation, as well as the best evidence to support its continued use in the care of complicated pregnancies.