A lack of iodine in the diet.

Iodine deficiency has many effects on growth and development. During pregnancy and the first few months after birth, it can cause problems for the baby that can't be fixed.

Iodine deficiency can cause irregular growth of the butterfly-shaped gland in the neck, called the thyroid gland. It can lead to an underactive thyroid. During pregnancy, the condition can be harmful to a growing baby's mental development.

Treatment includes iodine supplements. Complications need other treatments.