Effects of iodine on thyroid status of fetus versus mother in treatment of Graves' disease complicated by pregnancy.

Abstract

To investigate the effect of maternal iodine therapy for Graves' disease on fetal thyroid, we examined serum free T4 (FT4) and TSH levels in the fetus vs. those in the mother. Patients who were severely thyrotoxic were not included. Cord and maternal sera were tested at delivery in 35 patients with Graves' disease treated with iodine alone during pregnancy (6-40 mg daily). At the initiation of therapy, the mothers were at 11-37 weeks gestation, and FT4 levels ranged from 28.3-65.8 pmol/L. At delivery, maternal FT4 values ranged from 9.3-42.0 pmol/L, slightly above normal in 22 of the 35 mothers and normal in the other 13. Fetal FT4 levels were above the normal range occurred significantly less often than maternal levels (2 in 35; P less than 0.001), and no fetus had FT4 below normal. In the 13 mothers with normal FT4 levels, all fetal FT4 levels were normal; the fetal TSH level was above normal in 1 and normal in the remainder. A significant correlation was found between cord and maternal FT4 levels (P less than 0.05). In 12 of the 35 mothers, FT4 levels rose after a transient fall during iodine administration. The correlation of cord FT4 and maternal FT4 was closer when these 12 cases were excluded (P less than 0.001). Neither the dose of iodine nor the duration of therapy correlated with thyroid function in fetuses or mothers. Fetal TSH binding inhibitory antibody values strongly correlated with maternal TSH binding inhibitory antibody values (P less than 0.001). These findings indicate that 1) in the treatment of hyperthyroidism due to Graves' disease, iodine seldom if ever exposes the fetus to the risk of hypothyroidism; 2) the fetal thyroid is influenced by the same stimulatory and inhibitory factors as the maternal thyroid; and 3) escape from the inhibitory effects of iodine occurs less often in fetuses than in mothers, which may account at least in part for the lower thyroid status in the fetus compared to that in the mother.

Changes in Serum TSH Receptor Antibody (TRAb) Values in Patients with Graves' Disease after Total or Subtotal Thyroidectomy

“…The treatment of Graves' disease complicated by pregnancy is difficult, because the fetal thyroid is influenced by the same stimulatory and inhibitory factors as the maternal thyroid [37]. Uncontrolled hyperthyroidism or a high TRAb value during pregnancy is a risk for low birth weight (<2500 g), prematurity and eclampsia [28].…”

ENDOCRINOLOGY IN PREGNANCY: Pregnancy and the incidence, diagnosing and therapy of Graves’ disease

“…Thus, it was reported already in 1982 by Amino et al from Japan (13) that pregnancy may aggravate Graves' hyperthyroidism in early pregnancy and that worsening may also occur after delivery. On the other hand, a considerable proportion of pregnant women with GD experiences remission of the disorder during the second half of pregnancy (14,15). The late pregnancy decrease and the post-partum increase in risk of GD reflect general variation in thyroid autoimmunity, and similar changes occur in the concentrations of thyroid peroxidase and thyroglobulin autoantibodies in patients with Hashimoto thyroiditis (16) and in the incidence of hypothyroidism (17).…”

“…In Japan, iodine therapy has been successfully used to treat hyperthyroidism in pregnancy (14,56), with a significant reduction in birth defects compared with MMI therapy in a retrospective study (Fig. 5) (56).…”

THERAPY OF ENDOCRINE DISEASE: Antithyroid drug use in early pregnancy and birth defects: time windows of relative safety and high risk?

“…1). If biochemical signs of overt hyperthyroidism had developed, therapy could have been given with PTU, which appears to be associated with less severe birth defects (11), or if in Japan with pharmacological doses of iodine (41). Unfortunately, there is little recent experience with prolonged iodine therapy for hyperthyroidism in pregnancy outside of Japan.…”