Is fetal heart rate variability a good predictor of fetal outcome?

Objective. The purpose of this study was to investigate, in a prospective manner, whether fetal heart rate (FHR) variability serves as a reliable single predictor of fetal outcome. Methods. We undertook a prospective study of 2,200 consecutive deliveries. Preterms < 37 weeks, twins, stillbirths and fetal malformations were excluded from the study. FHR tracings were analyzed for variability in every delivery. Three windows were evaluated: 1) early in labor (30 min); 2) in the active phase of labor - 1 h prior to complete cervical dilatation (30 min); and 3) throughout the second stage of delivery, in segments of 30 min. Using the tracings taken at admission and prior to delivery, FHR variability was scored according to five previously used evaluative methods, and was correlated to the following three fetal outcome parameters: a) arterial cord blood pH < 7.2, > 7.2; b) 5-min Apgar > 6, < 7; and c) immediate outcome ('good' defined as newborn going home after 2-5 days, with no neonatal intensive care unit (NICU) admission). Results. 1. The majority of cases with adverse fetal outcome exhibited good FHR variability (mean, 80%). 2. Low FHR variability is not common in newborns with adverse general outcome (mean, 11.5%). 3. The predictability of FHR variability (using the five most common scoring methods) for evaluating adverse fetal outcome revealed low sensitivity (mean, 20.3%) and low predictive value (mean, 11.6%). Conclusion. FHR variability by itself cannot serve as the only indicator of fetal wellbeing. The presence of low variability should alert the physician; however, good FHR variability should not be interpreted as reassuring.