Head-to-body delivery interval using 'two-step' approach in vaginal deliveries: effect on umbilical artery pH

To assess the duration of head-to-body interval using a 'two-step' approach to delivery that include waiting for the next contraction to deliver the shoulders; and its effect on umbilical artery pH and neonatal outcome.

Prospective observational study on vaginal deliveries with singleton cephalic fetuses at term from June to December 2005. Clinical variables were evaluated in reference to umbilical artery pH and evidence of neonatal acidemia, defined as pH  ≤ 7.10 or base excess (BE) ≤ -12 in a multivariate model.

Head-to-body interval was timed and recorded in 789 deliveries. The mean head-to-body interval was 88 ± 61 s. Although head-to-body interval was significantly correlated to umbilical artery pH (p = 0.02), the decline in umbilical artery pH in relation to the head-to-body interval was clinically not significant (0.0078 units for every additional minute of the interval). At the multivariate analysis, umbilical artery pH  ≤ 7.10 and/or BE  ≤ -12 were significantly related to abnormal fetal heart rate tracing during the second stage (p = 0.012) and operative vaginal delivery (p = 0.045), but not to head-to-body interval (p = 0.25). Shoulder dystocia occurred in three cases (0.38%).

A 'two-step' approach to birth does not significantly increase the risk of neonatal acidemia.