Endocrine Abstracts

Several lines of evidence indicate an increased risk of adverse gestational outcomes in women with Hashimoto’s thyroiditis (HT) already as of TSH levels at early pregnancy >2.5mU/l, and definitely greater for TSH concentration >4mU/l. The latest guidelines recommend preconception TSH levels (pre-C-TSH) in HT women be maintained below 2.5mU/l, this threshold being expected to prevent hypothyroidism occurrence at early gestation.

Objectives: To perspectively evaluate: i) whether maintaining pre-C-TSH values <2.5mU/l in HT women was effective in preventing the occurrence of early gestation thyroid insufficiency, defined by TSH >2.5mU/l (diagnostic criteria 1) or >4.0mU/l (diagnostic criteria 2) at early gestation; ii) the cut-off values of TSH that would best preconceptionally identify euthyroidism at early gestation in HT women, by means of Receiver-Operating Characteristic (ROC) curves.

Methods: Two-hundred and sixty women preconceptionally diagnosed with HT and pre-C-TSH <2.5 mU/l, whose thyroid function was prospectively monitored from pre-conception up to pregnancy term.

Results: Of the 260 women, 122/260 (46.9%) were on LT4 therapy (Hypo-HT group) and 138/260 (53.1%) were confirmedly euthyroid without LT4 (Eu-HT group) prior to conception. At 1^st trimester, 37/122 (30.3%) Hypo-HT women had TSH >2.5mU/l, with almost 2/3 of these women (24/37, 64.9%) displaying TSH values >4.0mU/l. Analogously, at 1^st trimester evaluation TSH was >2.5mU/l in 42/138 (30.4%) EU-HT women, but >4.0 mU/l in 14/138 (10.1%) only. The optimal pre-conception TSH cut-offs found were 1.24mU/l and 1.73 mU/l for the diagnostic criteria 1 in Hypo-HT and Eu-HT women, respectively, and 1.74 mU/l and 2.07 mU/l for the diagnostic criteria 2 in Hypo-HT and Eu-HT women, respectively. Applying the above cut-offs, the relative risk reduction (RRR) of early gestational thyroid insufficiency was 82.7% and 94.0% for the diagnostic criteria 1 in Hypo-HT and Eu-HT women, respectively, and 82.5% and 97.9% for the diagnostic criteria 2 in Hypo-HT and Eu-HT women, respectively.

Conclusions: In our series, about one third of HT women whose pre-C TSH were in the range recommended by current guidelines (<2.5mU/l) required to increase or to start LT4 therapy once pregnant because of TSH levels exceeding the advisable TSH threshold at early pregnancy. In contrast, a more than halved rate of HT women whose pre-C serum TSH was below the calculated cut-offs was found to have unsatisfactory thyroid function at their first antenatal visit. The identification of population-specific pre-conception TSH cut-offs is in our view indicated, to optimize maternal thyroid function of HT women prior to conception.