**Core Concept**
External cephalic version (ECV) is a procedure where a healthcare provider attempts to manually rotate a fetus from a breech position to a cephalic (head-down) position. Fetal bradycardia, or a slower-than-normal fetal heart rate, can occur during this procedure due to potential umbilical cord compression or fetal distress.

**Why the Correct Answer is Right**
During ECV, if fetal bradycardia occurs, the next step is to **immediately deliver the baby via cesarean section**. This decision is based on the principle of prioritizing fetal well-being and safety. The American College of Obstetricians and Gynecologists (ACOG) recommends immediate delivery if fetal bradycardia occurs during ECV.

**Why Each Wrong Option is Incorrect**
**Option A:** Performing an ultrasound to assess fetal well-being - While an ultrasound may be helpful, it is not the immediate next step in this scenario.

**Option B:** Continuing the ECV procedure - This option would be inappropriate given the occurrence of fetal bradycardia.

**Option C:** Administering medication to stimulate fetal movement - There is no evidence to support this approach in the context of ECV complications.

**Clinical Pearl / High-Yield Fact**
Remember, fetal bradycardia during ECV is an indication for immediate delivery, as it can be a sign of umbilical cord compression or fetal distress.

**Correct Answer: D. Cesarean section.**