The nonstress test: the false negative test.

The nonstress test (NST) has been shown to be a reliable technique for the evaluation of fetal status. As a rule, a reactive NST, as opposed to a nonreactive NST, has been associated with a good pregnancy outcome. Nonetheless, fetal death has followed a reactive test. Because of the uncommon occurrence of a false negative NST, a retrospective investigation of the 2,226 patients who had undergone 4,500 NSTs was undertaken. Of these high-risk pregnancies, 1,564 women were delivered within 7 days of a reactive NST and there were four fetal deaths (0.026%). The presumed etiology for the four deaths was cord accident in three cases and abruptio placentae in one case. As with the false negative contraction stress test, the false negative NST appears to be associated with cord accidents, congenital anomalies, and abruptio placentae. Even though a reactive NST is associated with a low incidence of fetal death, close attention to the presence of fetal heart rate decelerations on the NST may be helpful in identifying those patients at risk for a cord accident and, theoretically, in reducing the incidence of fetal death. Even then, certain unavoidable situations can occur soon after a reactive NST, and, at present, no test of fetal well-being offers complete reassurance.