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

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.