Background: Increasing data suggest that subclinical hypothyroidism (SCH) and thyroid autoimmunity (TAI) are associated with adverse pregnancy outcomes, but there are limited data on the association of these conditions in early pregnancy with subsequent miscarriage. Methods: In this prospective cohort study, we screened 3315 women at low risk for thyroid dysfunction at four to eight weeks' gestation from iodine-sufficient areas of China between January 2012 and September 2012. Thyrotropin (TSH), free thyroxine (fT4), and the autoantibodies thyroid-peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) were measured. Based on these results, women were divided into four groups for comparison: euthyroidism (ET), isolated SCH, isolated TAI (positive TPOAb or/and TgAb), and SCH with TAI (SCH + TAI). The SCH group was stratified into two subgroups (SCH 1 and SCH 2) on the basis of the level of TSH (2.5 £ TSH < 5.22 or 5.22 £ TSH < 10 respectively). Accordingly, the SCH + TAI group was also stratified into two subgroups (SCH + TAI 1 and SCH + TAI 2). The outcome of interest was miscarriage, defined as spontaneous pregnancy loss prior to 20 weeks. Results: Compared to women with ET, the risk of miscarriage was significantly higher among women with SCH 2 (7.1% vs. .28]; p = 0.000). The gestational ages of 110 women at miscarriage were lower among women with subclinical thyroid abnormalities compared to ET (11.13 -3.21 weeks with subclinical thyroid abnormalities vs. 9.33 -1.71 weeks with ET; p = 0.024). In parallel with the higher TSH levels, there were earlier gestation ages at miscarriage between subgroups of SCH and SCH + TAI (SCH 1 vs. SCH 2: 10.79 -1.77 vs. 9.70 -1.47 weeks, p = 0.039; SCH + TAI 1 vs. SCH + TAI 2: 9.59 -1.97 vs. 8.88 -1.24 weeks, p = 0.031). Conclusions: Women with SCH and TAI are at an increased risk of miscarriage between four and eight gestational weeks. Women with a combination of SCH and TAI were found to have the highest risk and earlier gestational ages of miscarriage.
Subjects who were TPOAb and TgAb positive at baseline developed thyroid dysfunctions more frequently than seronegative subjects. High iodine intake was a risk factor for developing hypothyroidism in antibody-positive subjects. A constant exposure to excessive iodine intake increased the incidence of positive TgAb.
Objective: With the introduction of iodized salt worldwide, more and more people are exposed to more than adequate iodine intake levels with median urinary iodine excretion (MUI 200-300 mg/l) or excessive iodine intake levels (MUI O300 mg/l). The objective of this study was to explore the associations between more than adequate iodine intake levels and the development of thyroid diseases (e.g. thyroid dysfunction, thyroid autoimmunity, and thyroid structure) in two Chinese populations. Design: A population-based cross-sectional study was conducted in two areas in which people are exposed to different levels of iodine intake (Rongxing, MUI 261 mg/l; Chengshan, MUI 145 mg/l). A total of 3813 individuals were recruited by random sampling. Thyroid hormones, thyroid autoantibodies in serum, and iodine levels in urine were measured. B-mode ultrasonography of the thyroid was also performed for each participant. Results: The prevalence of subclinical hypothyroidism was significantly higher for subjects who live in Rongxing than those who live in Chengshan (5.03 vs 1.99%, P!0.001). The prevalence of positive anti-thyroid peroxidase antibody (TPOAb) and positive anti-thyroglobulin antibody (TgAb) was significantly higher for subjects in Rongxing than those in Chengshan (TPOAb: 10.64 vs 8.4%, PZ0.02; TgAb: 10.27 vs 7.93%, PZ0.01). The increase in thyroid antibodies was most pronounced in the high concentrations of TPOAb (TPOAb: R500 IU/ml) and low concentrations of TgAb (TgAb: 40-99 IU/ml) in Rongxing. Conclusions: More than adequate iodine intake could be a public health concern in terms of thyroid function and thyroid autoimmunity in the Chinese populations.European Journal of Endocrinology 164 943-950
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