ANTEPARTUM FETAL TESTING .2. ACCELERATION-CONSTANT RATIO - NONSTRESS TEST

For 0.5 h of undisturbed fetal monitoring periodic changes of the FHR [fetal heart rate] in response to spontaneous fetal movements (FM) were recorded. FM in patients who subsequently had positive OCT [oxytocin challenge test] were less likely to show accelerations (P = < 0.001) and more likely to show variable decelerations (P = < 0.001) and no change (P = < 0.001) in the FHR when compared with patients who did not have a positive OCT. A ratio between the number of FM associated with accelerations and the sum of FM associated with no change and decelerations was defined as the acceleration/constant (A/C) ratio. The outcome in patients who exhibited reactive tests (i.e., A/C ratio < 1) was more favorable than the outcome in patients with nonreactive tests (i.e., A/C ratio .ltoreq. 1). Patients with positive OCT universally showed nonreactive tests, whereas patients with false positive OCT were more likely to have reactive tests. The A/C ratio is evidently more predictive of the intrauterine environment than the OCT.