For a nulliparous patient in the first stage of labor with full cervical effacement and 5 cm dilation, what should the nurse do first after observing a gush of fluid?

In the scenario of a nulliparous patient in the first stage of labor who has experienced a gush of fluid, the most critical action for the nurse is to check the fetal heart rate (FHR). This step is essential because the gush of fluid may indicate the rupture of membranes (ROM), which can prompt various complications related to fetal well-being.

By assessing the fetal heart rate, the nurse can evaluate the condition of the fetus and determine if there are any signs of distress, such as variable decelerations, which could indicate umbilical cord compression. Monitoring FHR is vital in labor and delivery as it ensures the ongoing health of the fetus during the labor process, especially following a ROM event.

Other options, while important, are not immediately prioritized. Calling the doctor, documenting findings, and preparing for delivery are necessary tasks, but ensuring fetal safety through heart rate monitoring takes precedence in this situation to garner early intervention if needed.