THE INFLUENCE OF PREGNANCY AND REPRODUCTIVE SPAN ON THE OCCURRENCE OF AUTOIMMUNE THYROIDITIS

Abstract

A study comparing the reproductive histories of 89 women affected by Hashimoto's thyroiditis (HT) with 89 matched controls has been carried out to determine whether endogenous hormones contribute to the development of the disease. There was no evidence of an association between HT and parity and no trend to an increasing disease risk with increasing parity. However, patients with HT had a longer reproductive span. There was a significant trend to a lower risk with later age at menarche (relative risk (RR) of menarche at 13‐14 years compared with ≤ 12 years =0.71, and ≥ 15 years compared with ≤ 12 years = 0.45), and an increased risk with a later menopause (≥ 51 years compared with ≤ 50 years, RR = 3.00, P < 0.025). An additional finding was an increased hysterectomy rate among the cases. These observations may be explained if the hyperoestrogenic state associated with a longer reproductive span acted to modulate the immune process in autoimmune thyroid disease.