Problems with the thyroid can be caused by:

• iodine deficiency
• autoimmune diseases, in which the immune system attacks the thyroid, leading either to hyperthyroidism (caused by Graves’ disease) or hypothyroidism (caused by Hashimoto's disease)
• inflammation (which may or may not cause pain), caused by a virus or bacteria
• nodules, or non-cancerous lumps
• cancerous tumours
• certain medical treatments, including radiation therapy, thyroid surgery, and some medicines
• some genetic disorders

Occasionally, pregnancy can cause thyroid problems to start or get worse. If left untreated, this can cause problems for mother and baby, including miscarriage, premature birth, preeclampsia and bleeding after the birth.