The management of thyroid diseases during pregnancy requires special consideration because of the complexities that occur with the thyroid during pregnancy and also the fact that thyroid disease in the mother can affect the course of the pregnancy and the developing baby. 

            Maternal hypothyroidism, a condition in which the mother has too little thyroid hormone, may create a hypothyroid condition in the baby during a critical time when the brain is developing.  Also, hypothyroidism is associated with an increased risk of miscarriage or pre-term birth (three or more weeks prior to term).  Because of the harmful effects that hypothyroidism can have on the course of pregnancy, it is best that a woman knows whether she has this condition before becoming pregnant.  She should have normal thyroid levels before and during pregnancy.

            In addition, it is important for all women to know that thyroid dysfunction occurs in the first year postpartum in approximately 7 percent of all women--despite the fact that these women have had no known thyroid disease prior to pregnancy.  Because hypothyroidism is a potentially reversible cause of depression, women with postpartum depression should be tested for hypothyroidism and appropriately treated.  Much grief could be averted by prompt, knowledgeable attention to this problem.

            The most important cause of maternal thyroid deficiency, worldwide, is a deficiency of iodine in the diet although for women in the United States this may not be a problem.  However, as the need for iodine increases during pregnancy and breastfeeding, it is important that all pregnant and breastfeeding women take vitamins that contain iodine.  Among women who have an adequate intake of iodine, the main cause of hypothyroidism during pregnancy is an autoimmune thyroid disease known as Hashimoto's thyroiditis.  Other causes of hypothyroidism include prior treatment for hyperthyroidism and surgery for thyroid tumors.  Women with a family history of thyroid disease or any autoimmune disease have an increased risk for hypothyroidism.

            Guides based on The Endocrine Society's guidelines are available at www.hormone.org or 1-800-HORMONE.

--Excerpted from "The Hormone Foundation's Patient Guide to the Management of Maternal Hypothyroidism Before, During and After Pregnancy," August 2007