AMELIORATION OF SOME PREGNANCY-ASSOCIATED VARIATIONS IN THYROID-FUNCTION BY IODINE SUPPLEMENTATION

Knowledge of the effect of differences in iodine intake levels on publ ic health in areas with no endemic goiter is limited. Groups at risk w hen iodine intake is relatively low are pregnant and lactating women a nd their newborns. A prospective randomized study was performed to eva luate the effect of iodine supplementation in an area where the median daily iodine excretion in urine is around 50 mug. Fifty-four normal p regnant women were randomized to be controls or to receive 200 mug iod ine/day from weeks 17-18 of pregnancy until 12 months after delivery. In the control group, serum TSH, serum thyroglobulin (Tg), and thyroid size showed significant increases during pregnancy. These variations were ameliorated by iodine supplementation. Iodine did not induce sign ificant variations in serum T4, T3, or free T4. Cord blood Tg was much lower when the mother had received iodine, whereas TSH, T4, T3, and f ree T4 levels were unaltered. The results suggest that a relatively lo w iodine intake during pregnancy leads to thyroidal stress, with incre ases in Tg release and thyroid size. However, the thyroid gland is abl e to adapt and keep thyroid hormones in the mother and the child norma l, at least under normal circumstances, as evaluated in the present st udy. It is not known whether this stress is sufficient to be of import ance for late development of autonomous thyroid growth and function.