A first-time pregnant woman at 36 weeks of gestation is admitted to the labor and delivery unit because her membranes ruptured 30 minutes ago. The initial assessment indicates a 2 cm cervical dilation, 50% effacement, -2 station, vertex presentation, greenish- colored amniotic fluid, and contractions occurring every 3 to 5 minutes. There is a decrease in fetal heart rate after the last four contraction peaks. What should the nurse do first?