Sporadic accelerations during labor strongly indicate normal pH, whereas periodic accelerations do not: a case–control study

Abstract

Purpose To determine the association between the occurrence of sporadic and periodic fetal heart rate accelerations during labor and acidemia at birth. Materials and methods This is a case–control study of fetal heart rate patterns from 364 neonates with acidemia at birth (cord blood pH <7.05 at vaginal birth, or pH <7.10 at birth after first stage cesarean delivery) and 731 controls with pH ≥7.15. The last 30–60 min of the cardiotocographic traces before birth from the neonates born with acidemia and from the corresponding stage in labor for the controls were scrutinized. Odds ratios (OR) with 95% confidence interval for acidemia at birth were determined. Results During the first stage, ≥2 sporadic accelerations were present in 16% of cases and 78% of controls; OR for acidemia (compared to 0–1 accelerations) 0.05 (0.02–0.10). In the second stage, the corresponding rates were 13% and 60%, OR 0.09 (0.06–0.14). Isolated periodic accelerations were infrequent. A weak negative association between ≥2 periodic accelerations and acidemia (compared with 0–1 accelerations) was found in the second stage, OR 0.51 (0.30–0.86), but was not significant in the first stage, OR 0.24 (0.04–1.4). Even among fetuses with normal fetal heart rate variability (5–25 beats per minute) the occurrence of less than two sporadic accelerations was associated with an increased risk of acidemia, OR 10.3 (7.2–14.8). Conclusions Sporadic accelerations indicate a very low probability of acidosis but are absent in 40% of fetuses with normal pH during a 30–60 min second-stage recording.