Iwaki H, Ohba K, Okada E, et al. - In this retrospective study, researchers sought to examine the dose-dependent influence of antithyroid drugs (ATDs) on both maternal and fetal thyroid hormone status. This investigation was carried out at a tertiary hospital in Japan. They examined 62 pregnant women retrospectively who delivered between 2007 and 2016 and were treated with ATD at any stage during pregnancy for Graves’ hyperthyroidism. They chose people whose maternal free thyroxine (FT4) level data were available within 4 weeks of their deliveries and cord FT4 level of their infants at the time of delivery.  Those with multiple pregnancies, iodine or glucocorticoid treatment, and fetal goiter detected by ultrasonography have been excluded. Forty individuals were recruited after the exclusion criteria were applied. Cord FT4 levels in patients treated with high-dosage ATDs (methimazole >5 mg daily or propylthiouracil >100 mg daily) were significantly lower than maternal FT4 levels. Nevertheless, in patients treated with low-dosage ATDs (methimazole ≤ 5 mg daily or propylthiouracil ≤ 100 mg daily), there were no major variations between maternal and cord FT4 levels. The authors observed a dose-dependent impact of ATDs on the difference in serum FT4 levels between mothers with Graves’ hyperthyroidism and their neonates.