Title: Head-to-body delivery interval in “two-step” vaginal deliveries and umbilical artery pH
Abstract: To assess the normal head-to-body delivery time interval in a "two-step" assistance model (i.e. waiting for the next contraction if shoulders are not delivered after expulsion of the head before implementing maneuvers) and the effect of such an approach on umbilical artery (UA) pH. Prospective observational study on vaginal deliveries with single term cephalic fetuses in the period June-December 05. Maternal characteristics, fetal heart rate (FHR) tracing during first and second stage of labor (scored prospectively according to Boylan and Piquard), duration of phases of labor, presence of meconium, head-to-body delivery interval, number of contractions between head and body delivery, and use of ancillary maneuvers to complete delivery of the body were collected and related to UA pH in a multivariate model. The cohort consisted of 789 cases, 501 of which underwent continous FHR monitoring. Mean second stage duration was 32±22, head-to-body delivery interval was 88±61 sec, and 20 deliveries (2.5%) were operative. At multivariate analysis UA pH was significantly related to the duration of second stage of labor (P<0.01), to abnormal FHR tracing during the second stage (P<0.01), operative vaginal delivery (P=0.04), and head-to-body delivery interval (P=0.02). However, the decline in UA pH correlated to the head-to-body-delivery interval was clinically insignificant (R=−0.097, slope =−0.00013), since pH decreased by only 0.0078 units for every extra minute of the interval. Furthermore, there was no significant association between head-to-body interval and rate of umbilical cord acidosis, defined as pH<7.10 and or BE<−12 (P=0.2). A "two-step" birth assistance model leads to a prolonged head-to-body delivery time interval but it does not significantly increase the risk of neonatal acidosis.