Association between parity and autoimmune thyroiditis in a general female population

Background: Autoimmune thyroid disease (AIT) is more common in females than in males. Furthermore, it is well documented that the risk of thyroid autoimmunity increases during pregnancy and in the postpartum period. The objective of the present study was to analyse the association between parity and AIT by using ultrasound and serological data. Methods: The study population included 2156 women, aged 20-79 years. Serum thyroperoxidase antibodies (anti-TPO) and thyrotropin levels were measured and thyroid ultrasonography was performed. AIT was defined according to the combined presence of a hypoechogenic thyroid pattern and positive anti-TPO levels (200IU/ml). Odds ratios (OR) and 95% confidence intervals (CI) were calculated. Results: The analyses revealed an association between parity and AIT. Women with at least one pregnancy had increased odds for AIT (OR 4.6 [95%-CI 1.4-15.1], p0.05) compared to women who have never been pregnant. Similar results were observed using hypoechogenic thyroid pattern (OR 1.7 [95%-CI 1.0-2.9], p0.05) and positive anti-TPO levels (OR 1.8 [95%-CI 1.0-3.3], p=0.05) as separate dependent variables or using number of births as alternate independent variable. Conclusion: In this female population we found an association between parity and AIT and conclude that parity appears to be a potential risk factor for AIT.