High First Trimester Levels of TSH as an Independent Risk Factor for Gestational Diabetes Mellitus: A Retrospective Cohort Study

Although numerous articles have found an association between alterations in thyroid function and the risk of gestational diabetes mellitus (GDM), other studies have failed to demonstrate this association. This may be due to the different cut-off points used to define subclinical hypothyroidism. We aim to clarify the role of thyroid stimulating hormone (TSH) level in GDM within pregnant women with normal free thyroxine (fT4) levels. This retrospective cohort study was performed in 6775 pregnant women. The association between TSH and GDM was assessed by bivariate and multivariate logistic regression. Pregnant women with subclinical hypothyroidism are at significantly greater risk for GDM when compared with euthyroid pregnant women (OR = 1.85; 95% CI = 1.36–2.52). We have also observed that TSH levels increase the risk of GDM within euthyroid pregnant women, since the TSH levels between 2.5 and 4.71 showed a higher risk of GDM than those whose TSH levels are between 0.31 and 2.49 (OR = 1.54; 95% CI = 1.28–1.84). In addition, pregnant women with positive thyroid antibodies have almost 2.5 times the risk of developing GDM (OR = 2.47; 95% CI = 1.57–3.89). Our results support that in pregnant women with normal fT4 levels, higher first trimester TSH level implies a higher risk of GDM.