Nonstress testing.

Physiologic considerations on regulation of the fetal heart rate are reviewed. The types of fetal heart rate acceleration are classified and illustrated. Data from 509 patients undergoing 1,281 nonstress tests are presented, with emphasis on indications, technique, and interpretation. The nonstress test had a false negative rate lower than that of the contraction stress test. Since the false positive rate is high, a nonreactive test requires further evaluation. Progressive loss of baseline variability and decreasing frequency of accelerations appear to be early signs of fetal compromise.