This randomized clinical trial aims to compare the effect of the left lateral decubitus position versus the supine position on the duration of the active phase of labor in nulliparous women. A total of 188 participants will be randomly assigned to one of two groups. The intervention group will be placed in the left lateral decubitus position, while the control group will remain in the supine position. Both positions will be maintained for 30-minute intervals with 5-minute rest periods, continuing until delivery. The primary outcome is the duration of the active phase of labor. Secondary outcomes include rates of cesarean section, use of oxytocin and analgesics, and maternal and neonatal complications.