A new modality in nonstress testing: evaluation of beat-to-beat fetal heart rate variability.

Fetal monitoring equipment that provided accurate external measurement of the interval between each fetal heartbeat permitted the evaluation of beat-to-beat fetal heart rate (FHR) variability as part of routine nonstress testing. Nonstress tests (NSTs) were performed on 350 high-risk patients over a 12-month period. The beat-to-beat FHR variability and the reactivity of the last NST within 7 days of labor were analyzed in relation to the appearance of fetal distress during labor as indicated by late decelerations. Beat-to-beat FHR variability combined with nonstress testing was more predictive of subsequent fetal distress than nonstress testing alone. In all instances, complete loss of beat-to-beat FHR was followed by fetal distress during labor. Fetal distress was present in only 39% of labors following nonreactive NSTs. The inclusion of beat-to-beat FHR variability in nonstress testing can significantly aid in the detection of fetal compromise.