Comparative study of stressed and nonstressed antepartum fetal heart rate testing

Abstract

During an 18-month period 1328 nonstress tests (NST) and sequential contraction stress tests (CST) were performed on 566 patients. The criterion for reactivity was at least 2 accelerations associated with fetal movement during 20 minutes. The last test performed within 1 week of delivery was compared with perinatal outcome. A total of 1118 (84.2%) NSTs were reactive, and 210 (15.8%) were nonreactive. Of the CSTs 1249 (94.1%) were negative, 52 (3.9%) were positive, 16 (1.2%) were equivocal, and 11 (0.8%) were unsatisfactory. The correlation between a reactive NST and a negative CST was excellent (99.4%), whereas that between a nonreactive NST and a positive CST was poor (24.8%). Although the CST proved to be a better predictor of morbidity than the NST, both tests are highly significant predictors (P less than .001). Fetuses exhibiting both a nonreactive NST and a negative sequential CST are at no increased risk for morbidity. This study supports the concept that a precisely defined NST is an adequate screening tool for the evaluation of high-risk pregnancies.