Severe iodine deficiency is the leading cause of preventable mental retardation in the world today. Severe iodine deficiency in pregnant women is linked to miscarriage, stillbirth, and increased perinatal and infant mortality, as well as developmental problems in children, including cretinism - a condition that can involve severe mental retardation, deaf-mutism, and motor function problems.
According to studies, while the U.S. population typically is iodine sufficient, women of childbearing age are the subset of Americans most likely to have low iodine levels. Throughout the world, iodine deficiency affects over 2.2 billion people, and is most prevalent in South Asia, East Asia Pacific, and the East and South African regions.
In regions with severe iodine deficiency, pre-conception iodine supplementation has resulted in improved cognitive performance for children, and has significantly reduced the risk of cretinisim and other severe complications, including stillbirth, and neonatal and infant mortality.
In mild to moderately iodine-deficient women, studies have shown that supplementation improved outcomes for children. The key benefits seem to occur if iodine supplementation begins prior to conception, or occurs during the first 10 weeks of gestation. The benefits appear to drop off if supplementation begins after 10 to 20 weeks of gestation.
The Guidelines recommend that all pregnant and lactating women get a minimum of 250 mg iodine daily, and to accomplish that, should supplement diet with a daily oral supplement that contains 150 mg of iodine, in the form of potassium iodide.
To avoid the effects of excess iodine, the Guidelines point to the Institute of Medicine, which has defined the tolerable upper limit for daily iodine intake as 1100 mg/d (1.1 g/d) in all adults, including pregnant women. They recommend that pregnant women avoid sustained iodine intake from diet and dietary supplements that exceeds 500 to 1100 mg daily, to avoid concerns about fetal hypothyroidism.
In addition to diet and iodine supplements, pregnant women should be aware that there are other sources of iodine, including the heart drug amiodarone, which contains 75 mg iodine per 200 mg tablet, and iodine-based contrast agents used for medical tests, which can contain up to 380 mg of iodine per milliliter.
Stagnaro-Green, Alex, et. al. "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum." Thyroid. Volume 21, Number 10, 2011 (Online)