The nonstress test. Reassessment of the "gold standard"

The NST is simpler, less invasive, less time-consuming, and less expensive than its predecessor, the CST. It may be conducted in the outpatient setting with less skilled personnel. If the NST is to remain an important diagnostic modality, the issues of interpretative criteria, test conditions, and population composition must be reconsidered. In the future, authors must specify these data in detail and present their parameters of sensitivity, specificity, predictive values, and prevalence clearly. They also would be well advised to consider the value of adding other FHR information, such as baseline rate and variability to their interpretative criteria. Because clinical management--i.e., whether or not to intervene--may be influenced by or directly follow the outcome of an NST, it is even more important that such critical questions be addressed. The testing process should be cost effective, accurate, and sensitive enough to detect pregnancies at risk, yet specific enough to identify pregnancies that will have a good outcome. We believe that the issue of stand-alone NSTs should be examined for all indications and gestational ages commonly encountered. In our laboratory, current practice suggests that most conditions, at most gestational ages, benefit from an approach that combines the NST with amniotic fluid assessment and that uses age-adjusted standards to avoid misclassification of normal infants.