Preconception Thyrotropin Levels and Thyroid Function at Early Gestation in Women With Hashimoto Thyroiditis

Context Preconception optimization of thyroid function in women with Hashimoto thyroiditis (HT) is highly recommended to prevent/reduce the risk of thyroid insufficiency at early gestation. Objective This work aimed to evaluate the prevalence of first-trimester thyroid insufficiency in HT women with preconception thyrotropin (T-0-TSH) values consistently less than or equal to 2.5 mIU/L with or without levothyroxine (LT4) treatment, and to calculate T-0-TSH cutoffs that best preconceptionally identified HT women requiring first-trimester LT4 adjustment/prescription. Methods Serum TSH was obtained at 4- to 6-week intervals from 260 HT pregnant women (122 on LT4 [Hypo-HT]; 138 euthyroid without LT4 [Eu-HT]), prospectively followed from preconception up to pregnancy term. Receiver operating characteristic (ROC) curves were plotted to identify T-0-TSH cutoffs best predicting first-trimester TSH levels greater than 2.5 mIU/L (diagnostic criterion [DC] 1) and greater than 4.0 mIU/L (DC 2). Results At first trimester, TSH was greater than 2.5 mIU/L in approximately 30% of both Hypo-HT and Eu-HT women, and greater than 4.0 mIU/L in 19.7% Hypo-HT and 10.1% Eu-HT women (P = .038). The optimal ROC-based T-0-TSH cutoffs 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 DC 1 and DC 2, respectively. T-0-TSH values exceeding these cutoffs resulted in a statistically significantly increased risk of first-trimester thyroid insufficiency (odds ratio [OR] [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 DC 1 and DC 2, respectively). Conclusion The preconception TSH cutoffs that guaranteed a first-trimester TSH less than 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, and 1.74 mU/L and 2.07 mU/L in hypothyroid- and euthyroid-HT women, respectively, for a gestational target of 4.0 mU/L.