A RANDOMIZED TRIAL FOR THE TREATMENT OF MILD IODINE DEFICIENCY DURINGPREGNANCY - MATERNAL AND NEONATAL EFFECTS

One hundred and eighty euthyroid pregnant women were selected at the e nd of the first trimester of gestation on the basis of biochemical cri teria of excessive thyroid stimulation, defined as supranormal serum t hyroglobulin (TG >20 mu g/L) associated with a low normal free T-4 ind ex (<1.23) and/or an increased T-3/T-4 ratio (>25 x 10(-3)). Women wer e randomized in a double blind protocol into three groups and treated until term with a placebo, 100 mu g potassium iodide (KI)/day, or 100 mu g iodide plus 100 mu g L-T-4/day. Parameters of thyroid function, u rinary iodine excretion, and thyroid volume were monitored sequentiall y. Neonatal thyroid parameters, including thyroid volume by echography , were also assessed in the newborns from mothers of the three groups. In women receiving a placebo, the indices of excessive thyroid stimul ation worsened as gestation progressed, with low free T-4 levels, mark edly increased serum TG and T-3/T-4 ratio. Serum TSH doubled, on the a verage, and was supranormal in 20% of the cases at term. Urinary iodin e excretion levels were low, around 30 mu g/L at term. The thyroid vol ume increased, on the average, by 30%, and 16% of the women developed a goiter, confirming the goitrogenic stimulus associated with pregnanc y. Moreover, the newborns of these mothers had significantly larger th yroid volumes at birth as well as elevated serum TG levels. In both gr oups of women receiving an active treatment, the alterations in thyroi d function associated with pregnancy were markedly improved. The incre ase in serum TSH was almost suppressed, serum TG decreased significant ly, and changes in thyroid volume were minimized (group receiving KI) or almost suppressed (group receiving KI combined with L-T-4) Moreover , in the newborns of the mothers in the two groups receiving an active treatment, serum TG was significantly lower, and thyroid volume at bi rth was normal. The effects of therapy were clearly more rapid and mor e marked in the group receiving a combination of T-4 and KI than in th e women receiving KI alone. The differences could be partly attributed to the slightly higher amount of iodine received by women in the comb ined treatment. However, the main benefits of the combined treatment w ere almost certainly attributable to the hormonal effects of the addit ion of L-T-4. Furthermore, the study demonstrated that the administrat ion of T-4 did not hamper the beneficial effect of iodine supplementat ion. In conclusion, the present work emphasizes the potential risk of goitrogenic stimulation in both mother and newborn in the presence of mild iodine deficiency. Furthermore, the results clearly indicate the benefits of supplementing pregnant women with iodine and women with ex cessive thyroid stimulation (or a preexisting goiter) with a combinati on of iodine and L-T-4. In conditions of mild iodine deficiency, pregn ancy justifies monitoring thyroid function and volume, and therapeutic intervention to avoid hypothyroxinemia and goitrogenesis in both moth er and newborn.