E3-3. Secondary Analyses The investigators will perform other analyses aimed at obtaining adjusted assessments of treatment effectiveness, adjusting for baseline patient characteristics (covariates). The objectives of these analyses are to estimate the influence of covariates on the outcome and to use covariates to improve the estimated difference between treatment groups. The stepwise logistic regression model stratified by study site will be used to identify and estimate the effect of multiple prognostic factors on the probability of spontaneous vaginal delivery and other categorical outcomes. For continuous secondary outcomes such as duration of the second stage, the mixed model in which study site is treated as a fixed effect will be considered to adjust for prognostic factors. Interaction tests will be used to determine whether the effectiveness of the pushing strategy significantly differs across these subgroups. These analyses will be considered exploratory in nature and will not be viewed as providing confirmatory tests of hypotheses.