Antepartum electronic fetal monitoring interpretation: multicenter observational study

Antepartum EFM is the most widely used method worldwide to evaluate fetal well-being. However, neither NST nor other surveillance techniques can precisely determine the onset or degree of fetal hypoxemia and acidemia. The presence of accelerations seems to reflect fetal well-being; however, their absence does not predict fetal compromise. Evidence regarding the perinatal prognosis of normal NSTs with one or no accelerations compared with those classified as reactive remains insufficient.

To compare perinatal outcomes of the non-stress test (NST) interpreted by the usual reactive/non-reactive criterion versus the NST reported as "fetal well-being preserved" when there is one or no fetal heart rate (FHR) acceleration with moderate variability.

Multicenter, non-randomized, observational, comparative non-inferiority study evaluating two different NST interpretation criteria, conducted in Panama among high-risk pregnant patients with ≥ 34 weeks' gestation. A reactive NST was defined as a tracing with baseline FHR 110-160 beats per minute, variability 6-25 [beats/min], no bradycardia, and at least two accelerations within 20 min. When one or no acceleration was present while the other criteria were maintained, the NST was defined as showing "fetal well-being preserved" (normal/reassuring).

We analyzed 1,206 NSTs from 699 patients. There were no significant differences in gestational age at birth, time elapsed since the first NST, mode of delivery, 1- and 5-minute Apgar scores, or the presence of variable decelerations. No perinatal death was associated with follow-up by NST report. Twelve cases (0.99%) were reported as abnormal at the second NST performed 7 days after the initial NST. In those cases, no perinatal deaths occurred; two cases had a 5-minute Apgar < 7, one in each reporting group. Across the entire population, there were 6 deaths with no significant differences related to the initial NST reporting category.

This observational non-inferiority study reporting the NST as reactive (≥ 2 accelerations) or as fetal well-being preserved/reassuring (normal variability with ≤ 1 acceleration) yields no large differences in fetal well-being outcomes.