An Epidemiological And Basic Study On Postpartum Thyroiditis

Preface[Conception] Postpartum thyroiditis (PPT) is a common type of autoimmune thyroid diseases (AITD). According to the classification by Williams Textbook of Endocrinology, PPT belongs to type-3C of autoimmune thyroiditis, that is, transient thyroiditis. Actually, PPT is the result of potential thyroid autoimmune abnormity transforming to overt dysfunction state under the impact of pregnancy. Typical cases run a biphasic course during the first postpartum year, with a thyrotoxic phase being followed by a hypothyroid phase. It can also present as either phase of thyrotoxicosis or hypothyroidism. Part of patients may develop permanent hypothyroidism.[Status of the studies on PPT] PPT is a common disease in women of childbearing age. The prevalence of PPT varies from 1.1%-21.1% worldwide. Studies on the pathogenesis of PPT began in 1980s abroad. Traditional viewpoint seemed PPT as a transient and mild disease, while studies recently revealed PPT as one type of autoimmune thyroiditis. The occurrence of PPT may indicate a potential autoimmune thyroiditis, which converts into overt form when triggered by pregnancy. Prevention and cure of PPT are important for eugenics, for autoimmunity of thyroid can bring low serum thyroid hormones, resulting to adverse effects on mothers and offspring. It is complex in the pathogenesis of PPT. It concerns both endocrinology and immunology, relating to the effects of pregnancy on thyroid and immune system. Recently, studies on PPT extended into eugenics. So this is a typical multi-realm problem. Environmental factors, especially iodine, also influence the occurrence, development and prognosis of PPT. Animalexperiments and epidemiological studies have shown that excessive iodine can induce and aggravate AITD. In 2001, authoritative organizations defined firstly the term Iodine Excess. A few studies on iodine intake and PPT drew the contradictive results. In China, it has been empty in the realm of PPT, and no data on prevalence of PPT has been reported yet. It may be due to large samples needed, difficulties in follow-up survey and span among multi-subjects.[Contents in the study] The present study observed 488 pregnancy women prospectively for 6-12 months after their deliveries. (1) To obtain the first-hand epidemiological data on PPT in China; (2) To investigate the effects of iodine intake on the occurrence, development and prognosis of PPT; (I) To reveal the immunological mechanism of PPT, including thyroid autoantibodies, subgroup of T cells, activated T cells, regulatory T cells, Thl and Th2 cytokines and TGF Methods[Subjects] The study is a prospective study. 610 pregnant women were included in the cohort. 488 (80%) of them received follow-up survey for 6 months or more. Both patients with clinical or subclinical PPT diagnosed at the puerperal 6th month and some normal controls were followed until 1 year postpartum (pp).[Survey methods] We collected their fasting serum and urine in the day before delivery, 3 months pp, 6 months pp, 9 months pp and 12 months pp. Serum TSH, FT3, FT4, TPOAb, TgAb and TRAb and urinary iodine were measured. Also, we conducted B-ultrasound on the thyroids. Individual iodine nutrition was evaluated according to the average of one's urinary iodine concentration at different moments. We also collected anticoagulative blood from some of patients and controls for immunological study.[Diagnostic standard] (1) No history of thyroid diseases before delivery; (2) Thyroid dysfunction developed during the first half year-9-postparturition. PPT was classified as overt and subclinical according to free thyroid hormones. (3) Negative TRAb. It was to differentiate PPT with single thyrotoxicosis phase from postpartum GD (PPGD). Based on the thyroid dysfunction forms during the course of PPT, we classified PPT as 3 sub-types: hyperthyroidism followed by hypothyroidism (abbreviated as hyper-hypo type in the following text), hyperthyroidiam itself (abbreviated as hyper- type) and hypothyroidism without preceding hyperthyroidism (abbr...