J Korean Soc Endocrinol.  1998 Sep;13(3):339-350.

The Incidence of Postpartum Thyroiditis and Effect of High Iodine Intake on it in Korean Women

• Kim WB
• Yim CH
• Park KS
• Moon BS
• Lee JH
• Jun HW
• Jin HJ
• Kim SY
• Cho BY
• Lee HG

Abstract

BACKGROUND: Postpartum thyroiditis(PPT) is one of syndromes of thyroid dysfunction that occurs in the first year after parturition. Reported incidence of PPT is 3.9-8.2% of postpartum women in several studies from different countries. The fact that 52-100% of patients with PPT have thyroid autoantibodies, and that lymphocytic infiltration of thyroid gland is the characteristic pathological feature of PPT suggest that PPT is an autoimmune disease. High iodine intake in short term period is known to aggrevate the experimental autoimmune thyroiditis. This study was performed to investigate the incidence and clinical features of PPT in Korean postpartum women who usually ingest excessive amount of idine in immediate postpartum period and to investigate the predictive value of thyroid autoantibodies in the development of PPT in them. METHOD: Between March 1996 and February 1997, 99 women without previous history of any thyroid disease who delivered babies at Boramae hospital were enrolled. Thyroid function parameters(T3, T4, free T4, TSH), thyroid autoantibodies(anti-microsomal antibody, anti-thyroglobulin antibody) and urinary iodine excretion were measured prospectively before and 1, 3 months after delivery. Dietary iodine intake during postpartum period was evaluated by questionnaire, and clinical parameters were followed up.
RESULTS
During 3 months of observation, PPT developed in 8.1%(8/99) of postpartum women. Five cases had typical course having thyrotoxic phase and the other 3 cases had hypothyroid phase without toxic phase. However, only one of those required thyroid hormone replacement therapy in the latter group. There were no differences in age, baseline thyroid function parameters, parity, percent cases with family history of thyroid disease between those developed PPT (n=8) and those did not develop PPT(n=91). Duration of high iodine intake(3.8 +- 0.5 wk. vs. 3.7 +- 0.8 wk., p>0.05), total ingested amount of high iodine diet(77 +- 28 vs. 79 +- 24 bowels of miyokguk, p)0.05), and the urinary iodine excretion(1.9 +- 1.4 mg/g creatinine vs. 3.7 +- 3.7mg/g creatinine, p0.05) at 1 month postpartum were not different between two groups. Of 99 total subjects, anti-microsomal antibody(AMA) was present in 13.1%(13/99) before delivery in their sera. Positive predictive value of the presence of AMA before delivery in predicting the development of PPT was 30.8%.
CONCLUSION
The fact that incidence of PPT in normal Korean postpartum women who usually have high iodine intake in immediate postpartum period is not higher than those of other countries, and that there was no difference in the amount of iodine intake between those developed PPT and those did not suggest that high iodine intake in immediate postpartum period do not influence on the incidence of PPT. The presence of AMA before delivery had low specificity in prediction of development of PPT, so the measurement of AMA seems not to be a useful screening test.

MeSH Terms

Autoantibodies
Autoimmune Diseases
Creatinine
Female
Hormone Replacement Therapy
Humans
Incidence*
Iodine*
Mass Screening
Parity
Parturition
Postpartum Period*
Postpartum Thyroiditis*
Prospective Studies
Surveys and Questionnaires
Sensitivity and Specificity
Thyroid Diseases
Thyroid Gland
Thyroiditis, Autoimmune
Autoantibodies
Creatinine
Iodine