Preconception Thyrotropin Levels and Thyroid Function at Early Gestation in Women with Hashimoto's Thyroiditis

Context: Preconception optimization of thyroid function in women with Hashimoto's thyroiditis (HT) is highly recommended to prevent/reduce the risk of thyroid insufficiency at early gestation. Objectives: To evaluate the prevalence of 1st-trimester thyroid insufficiency in HT women with preconception thyrotropin (T0-TSH) values consistently ≤2.5 mIU/L with or without l-T4 treatment; to calculate T0-TSH cut-offs that best preconceptionally identified HT women requiring 1st-trimester l-T4 adjustment/prescription. Methods: Serum TSH was obtained at 4-6 week intervals from 260 HT pregnant women (122 on l-T4 [Hypo-HT]; 138 euthyroid without l-T4 [Eu-HT]), prospectively followed from preconception up to pregnancy term. ROC-curves were plotted to identify T0-TSH cut-offs best predicting 1st-trimester TSH levels >2.5 mIU/L (diagnostic criterion [dc]-1) and >4.0 mIU/L (dc-2). Results: At 1st-trimester, TSH was >2.5 mIU/L in ∼30% of both Hypo-HT and Eu-HT women, and >4.0 mIU/L in 19.7% Hypo-HT and 10.1% Eu-HT women (p 0.038). The optimal ROC-based T0-TSH cut-offs found were: 1.24 mIU/L/1.74 mIU/L in Hypo-HT, and 1.73 mIU/L/2.07 mIU/L in Eu-HT women, for the dc-1 and -2, respectively. T0-TSH values exceeding the above cut-offs resulted in a significantly increased risk of 1st-trimester thyroid insufficiency (ORs[95%CI)] 15.92[5.06-50.15] and 16.68[5.13-54.24] in Hypo-HT; 16.14[6.47-40.30) and 17.36[4.30-70.08] in Eu-HT women, for the dc-1 and -2, respectively). Conclusions: The preconception TSH cut-offs that guaranteed a 1st-trimester TSH < 2.5 mU/L in hypothyroid- and euthyroid-HT women were, respectively, almost 50% (1.24 mU/L) and 30% (1.73 mU/L) lower than this gestational target, and1.74 mU/L and 2.07 mU/L in hypothyroid- and euthyroid-HT women, respectively, for a gestational target of 4.0 mU/L.