C1. Recruitment The investigators will employ familiar efficient recruitment techniques we have used in recent randomized trials in the same settings. All women admitted to the labor and delivery units of the participating medical centers will be screened against inclusion and exclusion criteria. Eligible subjects will be approached for written consent to participate in the study once they are committed to a vaginal delivery attempt. Although consent to participate will be obtained irrespective of cervical dilation, randomization will be performed only when complete cervical dilation is confirmed. This is necessary to avoid situations in which subjects are randomized and subsequently undergo cesarean delivery in the first stage of labor for indications such as failure to progress or non-reassuring fetal heart tracing.