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Context: Early treatment is essential to avoid the cardiac complication of neonatal hyperthyroidism (NH). Our results have direct implications for clinical care. Objective: NH can cause potentially fatal neonatal thyrotoxicosis. Here, we have evaluated the feasibility of neonatal hyperthyroidism screening using the thyroid-stimulating hormone value in dried blood collected routinely on filter paper on the third postnatal day of life for congenital hypothyroidism screening. Methods: Retrospective case–control study. Cases were identified using data from our previously published study of 280 000 infants born in 10 maternity units in France in 2007-2014. Controls were identified among the 1 362 564 infants born in the Ile-de-France region during the same period. Results: A screening thyroid-stimulating hormone level below 0.18 mIU/L on the third postnatal day had 71% (95% CI 44-90%) sensitivity, 99% (95% CI 99-100%) specificity, 81% (95% CI 74-86%) positive predictive value, and 98% (95% CI 97-99%) negative predictive value for detecting severe NH. By univariate regression analysis, the screening thyroid-stimulating hormone value was the strongest predictor of NH (P < .00001), with an area under the receiver-operating characteristics curve of 0.98 (95% CI 0.95-1.0). Expected frequencies were not significantly different from observed frequencies (Hosmer–Lemeshow test, P = .99). Conclusion: The screening thyroid-stimulating hormone test can be used to detect severe NH, the optimal cut-off being 0.18 mIU/L. The additional cost compared with screening for congenital hypothyroidism would be small. Infants with neonatal hyperthyroidism would benefit from an earlier diagnosis with treatment initiation at the presymptomatic stage in many cases, ensuring optimal outcomes. [ABSTRACT FROM AUTHOR]

A case is presented of foetal compensated hypothyroidism due to persisting low maternal serum FT4 at the beginning of pregnancy. Diagnosis was made by means of foetal ultrasound followed by foetal blood sampling because of atypical findings. Foetal thyroid hypertrophy resolved progressively as exogenous thyroxine was administered to the mother. This case highlights once again the importance of adequate thyroid function during pregnancy. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]