The thyroid is a small gland located in the front of the neck under the Adam's apple. It produces thyroid hormone, a chemical that regulates the body's metabolism. A swollen thyroid, which doctors call goiter, may occur for many reasons, such as when the thyroid does not produce enough hormone, reports MayoClinic.com.
Autoimmune Disease
Autoimmune disorders, which occur when malfunctioning immune cells attack the thyroid gland, produce low thyroid levels and cause the gland to swell, reports MayoClinic.com. Hashimoto's disease, an autoimmune disorder that slowly destroys the thyroid, is the most common cause of low thyroid in Americans.
Pregnancy
The thyroid gland can swell and thyroid levels can drop during pregnancy, particularly during the first trimester, reports "Thyroid Disease and Pregnancy." These conditions occur because pregnancy hormones temporarily influence the thyroid, causing it to produce too few chemicals. A swollen thyroid and inadequate thyroid levels are more common in pregnant women who consume too little iodine in their diets. Iodine deficiency also can cause the condition.
Thyroiditis
Thyroiditis, or inflammation of the thyroid gland, is caused by a viral infection or an attack by the autoimmune system on the thyroid, explains "Hypothyroidism." This disorder causes the thyroid gland to deposit its entire supply of stored thyroid hormone in the bloodstream all at once, causing an overactive spike followed by low thyroid levels.
