Objective: To review the iodine status of women as assessed through National Health and Nutrition Examination Surveys from 1971 to 2002.

Design and Setting: National normative estimates of iodine status of the civilian, non-institutionalized population in the United States of America.

Subjects: Women of reproductive age and pregnant women.

Results: In the United States of America, iodine began to be added to the diet in the 1920s. An excessive iodine intake was documented by the first National Health and Nutrition Examination Survey (NHANES I) in the 1970s which reported a median urinary iodine (UI) concentration of 320 μg l-1. In the NHANES III survey, conducted between 1988 and 1994, the median UI concentration had decreased to 145 μg l-1, while 14.9% of women aged 15-44 years and 6.9% of pregnant women had a UI concentration 50 μg l-1. The concentrations of serum T4 and thyroid-stimulating hormone of women with a low UI concentration did not, however, indicate an iodine deficiency.

Conclusions: Further studies of the association between iodine excretion and biochemical and physiological changes should be undertaken to better understand women's needs for iodine and to develop criteria to monitor them in pregnancy. Because of the potential harm caused by iodine deficiency during pregnancy, we support the use of iodine supplements for all pregnancies while these data are being collected.

Objective: To examine the importance of iodine nutrition during pregnancy.

Design: Review of existing literature of iodine in pregnancy.

Setting: Population surveys and metabolic studies.

Subjects: Pregnant women.

Results: The main changes in thyroid function associated with pregnancy are due to an increase in hormone requirements that begin in the first trimester of gestation. This increase can only be met by a proportional increase in hormone production, something that depends directly upon the availability of iodine. When dietary iodine is lacking, an adequate physiological adaptation is difficult to achieve and is progressively replaced by pathological alterations that occur in parallel with the degree and duration of iodine deprivation.

Conclusions: Iodine prophylaxis should be given systematically to women during pregnancy. In most public health programmes dealing with the correction of iodine deficiency disorders, iodised salt has been used as the preferred means to deliver iodine to households. Iodised salt, however, is not the ideal means of delivering iodine in the specific instances of pregnancy, breast-feeding and complementary feeding because of the need to limit salt intake during these periods. In European countries, presently it is proposed that iodine is given to pregnant women and breast-feeding mothers by systematically administering multivitamin tablets containing iodine in order to reach the recommended dietary allowance of 250 μg iodine day-1.