Postpartum Thyroid Dysfunction in Pregnant Thyroid Peroxidase Antibody-Positive Women Living in an Area with Mild to Moderate Iodine Deficiency: Is Iodine Supplementation Safe?

Abstract

In moderately iodine-deficient, pregnant, thyroid peroxidase antibody (TPO-Ab)-positive women the role of iodine supplementation in the development of postpartum thyroid dysfunction (PPTD) was studied in a placebo-controlled, randomized, double blind trial. Screening for TPO-Ab was performed in early pregnancy in a population of healthy pregnant Danish women with no previous diagnosed thyroid disease (prevalence, 117 of 1,284; 9.1%). The participants were randomized, stratified according to TPO-Ab level, to three groups. All participants received a daily vitamin and mineral tablet with 150 microg iodine or no iodine. The +/+ group received iodine during pregnancy and the postpartum period, the +/- group received iodine during pregnancy only, and the -/- group received no iodine supplementation. A total of 66 TPO-Ab positive women were followed, and in the postpartum period sera were collected at 8-week interval for biochemical evaluation of thyroid function and antibody level. Compliance was evaluated by 24-h urinary iodine measurements. PPTD developed in 55% of the participants. In 67% of the cases abnormal TSH was accompanied by abnormalities in thyroid hormones, whereas 33% had abnormal serum TSH only. There was no statistically significant difference in the frequency of PPTD in the three groups: +/+ group, 59% (95% confidence interval, 36-79%); +/- group, 60% (36-81%); and -/- group, 46% (26-67%). There were also no differences in the severity of the PPTD, as evaluated by duration and grade of deviation of TSH and thyroid hormones from normality. The occurrence, severity, and type of PPTD predominantly depended on the TPO-Ab level: TPO-Ab below 200 U/L at screening, 35% developed PPTD; TPO-Ab of 200-900 U/L, 54%; and TPO-Ab above 900 U/L, 75% developed PPTD. Women with low levels of antibodies predominantly remained euthyroid or had hyperthyroidism only, whereas women with high antibody levels had hyperthyroidism followed by hypothyroidism or hypothyroidism only. We conclude that iodine supplementation (150 microg) during pregnancy and the postpartum period to TPO-Ab-positive women living in an area with mild to moderate iodine deficiency did not induce or worsen PPTD. The study confirmed that screening for TPO-Ab in early pregnancy can predict women at high risk for development of PPTD.

High prevalence of autoimmune thyroiditis in patients with polycystic ovary syndrome

“…Out of 175 PCOS patients, 36 had overt AIT (20.6%), 47 patients (26.9%) were positive for thyroid-specific autoantibodies, and two more patients had Graves' disease, compared with 11 out of 168 controls (6.5%) with AIT, and 14 (8.3%) controls positive for thyroid-specific autoantibodies. The prevalence of 8.3% in our controls was comparable to a previous small study also conducted at the University of Essen, that found 7 out of 70 (10%) pregnant women positive for thyroid antibodies (22), and a recent study on healthy pregnant Danish women (prevalence of TPO antibodies, 117 of 1284; 9.1%) that matched our sample for age, moderate iodine deficiency and no previous diagnosed thyroid disease (23). In another Danish study on 2656 subjects aged 41 to 71 years (on average 12 to 42 years older than our controls) a prevalence of positive TPO antibody titers was found in 16.9% of women and 6.6% of men (24).…”

Thyroglobulin as a Biomarker of Iodine Deficiency: A Review

“…One of the studies (80) assessed Tg concentration in the first trimester before supplementation and then again at two weeks postpartum; one study (81) assessed Tg in the first and third trimesters; and one study (82) assessed Tg in all three trimesters and again 12-24 weeks postpartum. Tg concentrations in women in the first trimester (i.e., at baseline before supplementation) ranged from 13 to 25 lg/L, and postpartum, in women that had received any type of additional iodine (i.e., supplements or iodized salt), Tg ranged from 8 to 18 lg/L.…”

Symposium on ‘Geographical and geological influences on nutrition’ Iodine deficiency in industrialised countries

“…The adverse effects on pregnancy of mild iodine deficiency, typical of industrialised countries, remain unclear. Six controlled trials of iodine treatment in pregnant women with iodine deficiency have been conducted in Europe (21)(22)(23)(24)(25)(26) . Overall, these studies suggest that in areas of mild-to-moderate iodine deficiency the maternal thyroid is able to adapt to meet the increased thyroid hormone requirements of pregnancy (27) .…”