Characterization and prognostic significance of severe variable decelerations in the second stage of labor

OBJECTIVE: The characteristics of variable decelerations (VD) in the second stage oflabor 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. STUDY DESIGN: In this descriptive study, fetal heart tracings containing VD from 243 singleton, vaginal deliveries between 6/94 and 7/96 were reviewed blinded to outcome information. Excluded were: (1) deliveries at <36 weeks, (2) uninterpretable tracing, (3) absence of VD in 2nd stage of labor and (4) absence of exam establishing beginning of 2nd stage oflabor. VD characteristics evaluated: shape (U, V, W); anterior and posterior "shoulders": slow return to baseline (30 degree curve); cumulative depth of VD per 10 minutes. Outcome information collected: 2nd stage oxytocin dose, method of deliver)', birthweight and Apgar scores. Statistical analysis included regression and ANOVA. RESULTS: The mean maternal age was 32 ±5 years, GA 39 ±1.3 weeks, oxytocin dose 3 ±5 mu/min, and length of the second stage 65 ±57 minutes. The total number of VD averaged 21 ±17 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 oflabor (R = .85, P < .001). The total number and percentage of VD <70 bpm were negatively correlated with 5 minute Apgar score (P = .038, .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 = .08, .72, .73, .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 = .002); but no significant differences in Apgar scores compared with those with spontaneous delivery (P = .9). CONCLUSIONS: Second stage VD < 70 bpm were significantly associated with lower five minute 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 minute Apgar scores.