Although electronic fetal monitoring (EFM) has been used for many years as an aid to predict acidemia, the indeterminate nature of the EFM patterns indicates the need for a reassessment of the nomenclature and categorization of the traditional 4 deceleration patterns, developed by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). None of these patterns (variable, early, late, prolonged) has consistently been associated with fetal acidemia or birth outcome. This 4-year, retrospective cohort study was designed to determine the ability of non-NICHD measures of EFM patterns compared with the NICHD nomenclature to predict fetal acidemia.
From 8622 admissions, 5388 women were included; all had a singleton, nonanomalous fetus at 37 weeks’ gestation or greater and reached the second stage of labor. Detailed maternal and infant data were obtained from medical records. The primary exposure was the characteristics of the EFM tracing 30 minutes before delivery. Electronic fetal monitoring extraction was done using the NICHD criteria for contractions and EFM patterns along with duration, depth, and number of decelerations. Women who delivered an infant with acidemia (pH ≤7.10) were compared with those who delivered nonacidemic infants (pH >7.10).
Fifty-seven infants (1.1%) had acidemia; 5331 (98.9%) did not (pH >7.10). Of the NICHD categories, none showed significant association with acidemia when assessed in the last 10-minute interval or in the last 30 minutes before delivery. When compared with moderate variability, minimal variability was not associated with acidemia. Because marked and absent variability occurred rarely, an estimate could not be made. Repetitive late, prolonged, and variable decelerations were all significantly associated with acidemia after adjusting for obesity, fever, prolonged first stage, and nulliparity; respective areas under the curve (AUCs) were 0.78, 0.81, and 0.79. Tachycardia was significantly associated with acidemia (AUC, 0.80), whereas bradycardia did not occur in the neonates with acidemia and rarely in those without acidemia. In the final 30 minutes, infants with acidemia, on average, had 9 decelerations compared with 6 in those without acidemia; acidemic infants also had more severe decelerations (nadir of ≤60 beats/min) and a larger total deceleration area. In the 10 minutes before delivery, repetitive late, variable, and prolonged decelerations and tachycardia were again significantly associated with neonatal acidemia. A non-NICHD measure, total deceleration area (median, 21,116.0 for acidemia; median, 8940.0 for no acidemia), demonstrated a greater association with acidemia (AUC, 0.83; P = 0.04).
Although the 4 factors within the NICHD system were associated with acidemia, alone or combined, they were not associated with acidemia as well as the total deceleration area, which indicates deceleration frequency and depth. The existing system for quantifying EFM patterns should be reexamined to create a more descriptive system.