How can a goiter be prevented?

Usually it can't: Iodine deficiency goiter is really the only preventable cause of thyroid enlargement. This is extremely uncommon in western societies. If you are developing a goiter, some doctors may suggest thyroid hormone supplementation to "suppress" the goiter, but this generally isn't terribly effective.

Keep appoinments: It is important to keep all scheduled appoinments and learn of the signs. If they start occurring then don't wait to be seen.