Autoimmune thyroid disease (AITD) is the most common autoimmune disorder. Evidence regarding high prevalence and incidence of thyroid autoimmunity in women, and specially women of reproductive age, is still inconclusive and previous studies have suggested genetic, environmental, and existential factors to play a role in it s pathogenesis. In this study, we aimed to investigate the effect of parity and other reproductive factors on incidence of thyroid autoimmunity within the framework of the Tehran Thyroid Study.
The present study was conducted within the framework of the Tehran Thyroid Study (TTS) and 1999 non pregnant euthyroid TPOAb negative women were followed up for an average of 8.3 years. Pooled logistic regression model was used to assess the association (odds ratio) between time-dependent covariates parity, menopause and abortion and incidence of TPOAb positivity.
Total incidence rate of TPOAb positivity were of 8.65(7.35,10.18) per1000 person-year. We found no significant association between changes in the number of parity and risk of developing TPOAb using multiple pooled logistic models both as crude effect and after adjustment for age, BMI and smoking; similarly, there was no association between changes of parity, menopause and abortion status and incidence of TPOAb positivity.
Parity does not seem to have an independent role in triggering thyroid autoimmunity but vast immunological and physiological changes during pregnancy may act as a precipitating factor in context of other genetic and environmental etiologies.