Final answer:
If the fetal heart rate can no longer be determined using external methods, internal monitoring can be used as an alternative method.
Step-by-step explanation:
If the *fetal heart rate* can no longer be determined using *external methods*, alternative methods can be used such as *internal monitoring*. Internal monitoring involves placing an electrode on the baby's scalp or attaching a small sensor to the baby's scalp during labor. This allows for a more accurate and continuous measurement of the fetal heart rate.