Characterization and Prognostic Significance of Variable Decelerations in the Second Stage of Labor

ABSTRACT

The characteristics of variable decelerations (VD) in the second stage of labor and the relationship between the number, frequency, or severity and neonatal outcome have not been studied. We have analyzed the characteristics of VD in the second stage of labor and their prognostic significance in the prediction of Apgar scores. In this descriptive study, fetal heart tracings containing VD from 250 singleton, vaginal deliveries between June 1994 and July 1996 were reviewed blinded to outcome information. Excluded were: (1) deliveries at <36 weeks, (2) uninterpretable tracing, (3) absence of VD in second stage of labor, and (4) absence of exam establishing beginning of second stage of labor. VD characteristics evaluated: shape (U, V, W); anterior and posterior “shoulders”; slow return to baseline (≤ 30-degree curve); cumulative depth of VD per 10 min, second stage oxytocin dose. Outcome information collected: method of delivery, birth weight and Apgar scores. Statistical analysis included regression and analysis of variance (ANOVA). The mean maternal age was 32 ± 5 years and gestational age 39 ± 1.3 week. In the second stage of labor, the mean oxytocin dose was 3 ± 5 mu/min, length of the second stage 65 ± 57 min, total number of VD averaged 21 ± 1 7 and uterine contractions 26 ± 22 per patient. The percentage of VD <100 bpm was 50 ± 27%, VD <70 bpm 13 ± 20%, anterior shoulders 76 ± 30%, posterior shoulders 75 ± 30% and slow return to baseline 12 ± 17%. The number of VD significantly increased with the length of the second stage of labor (r = 0.85, p <0.001). The total number and percentage of VD <70 bpm were inversely correlated with 5-min Apgar score (p = 0.038, 0.015 respectively). The sum of the depth of VD/length of second stage as well as the percentage of VD with anterior and/or posterior shoulders and slow return to baseline were not significantly related to Apgar scores (p = 0.08, 0.72, 0.73, 0.99, respectively). Patients with a higher percentage of decelerations with slow return to baseline had a higher rate of operative vaginal deliveries (20 vs. 11%, p = 0.002); but no significant differences in Apgar scores compared with those with spontaneous delivery (p = 0.9). Second stage VD <70 bpm were significantly associated with lower 5-min Apgar scores. Although the presence of VD with a slow return to baseline was significantly associated with operative delivery, there was no difference in 5-min Apgar scores.

Keywords

Variable decelerations - fetal heart rate tracing - second stage of labor