B1. Design Overview This is a multicenter randomized trial of nulliparous women to compare the effectiveness of immediate and delayed pushing in the second stage of labor. The investigators aim to test the central hypothesis that immediate pushing in the second stage of labor increases spontaneous vaginal delivery, shortens duration of the second stage, and reduces adverse neonatal and maternal outcomes. The investigators chose a randomized controlled trial, the 'gold standard' of clinical research design, with the goal of obtaining the highest quality evidence to inform clinical practice. Randomly allocating subjects to different interventions minimizes selection bias and results in groups that are comparable with regards to important confounding variables, both measured and unmeasured. Additionally, the broad inclusion criteria, simplicity in relationship of the interventions to current practice, and the multicenter design with regional representation and practice diversity increase generalizability and direct application of the findings.