The associations between parity, abortion, and menopause status with the prevalence and incidence of thyroid dysfunctions: 12-year follow-up of Tehran Thyroid Study

Background: The effect of thyroid dysfunctions on the female reproductive system is well recognized. Although many studies pointed out the possible effect of female reproductive status alteration on thyroid function, there are too many contradictions to come up with an exact conclusion. This study aimed to investigate the associations of parity, abortion, and menopause status with the prevalence and incidence of thyroid dysfunctions. Methods From the Tehran Thyroid Study (TTS) population, 2191 euthyroid female participants at baseline were selected and followed up in three-year intervals. Multivariable Cox proportional hazard model was used to determine associations between the incidence of thyroid dysfunctions with parity, abortion, and menopause status; age, smoking, body mass index, and thyroid peroxidase antibodies positivity were adjusted. Results At the baseline, multiple parities were significantly associated with overt hypothyroidism (OR, 95% CI: 1.12, 1.0-1.26) and subclinical hyperthyroidism (OR, 95% CI: 1.11, 1.03–1.21). Likewise, multiple abortions were associated with overt hyperthyroidism (OR, 95% CI: 2.09, 1.02–4.26). Multiple parities (≥ 4) significantly increased the risk of incident subclinical and clinical hypothyroidism. Moreover, the incidence of overt hypothyroidism significantly decreased in mothers with a history of abortion. No significant associations between menopause status with the prevalence and incidence of hypothyroidism or hyperthyroidism were observed. Conclusions There are relationships between parity and abortion with thyroid function. Understanding the exact mechanism requires more information at the cellular and molecular level on signaling cascades alterations during pregnancy.