Electronic fetal monitoring: what's reassuring?

To determine which combinations of fetal heart rate pattern abnormalities are associated with normal outcome in term pregnancies.

A cohort of 2200 consecutive deliveries was examined and the fetal heart rate tracings analyzed. Singleton, term patients without chorioamnionitis or serious malformations were used to perform logistic regression analysis to select those FHR patterns associated with increased risk for Apgar<7 and cord pH<7.15, or immediate adverse outcome.

Patients having no fetal heart rate abnormalities, mild variable decelerations, decreased variability, mild bradycardia, or accelerations present, constituted 84% of all fetal heart rate tracings. These tracings alone, or in combination, predicted 5 minute Apgar score> or =7 in 99.7%, cord pH> or =7.15 in 96.9% and no adverse neonatal sequelae in 96.2% of cases. Accelerations were reassuring regardless of FHR pattern. When these patterns were not present, non-reassuring tracings, the risk for immediate adverse outcome increased 50%. The non-reassuring tracings were both without accelerations and had tachycardia, prolonged bradycardia, severe variable or late decelerations, or a combination of these patterns. This increased risk was independent of the risk of confounders: i.e. thick meconium (1.8-fold), prolonged second stage of labor (>50 min., 1.5-fold), maternal disease (e.g. kidney, respiratory, 3-fold), or hypertensive disease (1.9-fold).

The great majority of fetal heart rate pattern abnormalities can be considered reassuring as they are within normal variations of a healthy fetus. The non-reassuring ones identify infants that truly require further evaluation by fetal scalp, vibroacoustic stimulation, or fetal scalp blood sampling.