Navigating Therapy for Hyperthyroidism in Lactation: A Case Report and Review of Antithyroid Drug Safety

Abstract

Graves’ disease is the leading cause of hyperthyroidism in women of reproductive age and may relapse in the postpartum period, when immune reactivation and the desire to continue breastfeeding complicate antithyroid drug selection. This case report aims to describe the therapeutic decision making process in a breastfeeding mother with Graves’ hyperthyroidism and to provide practical insights that help bridge the gap between guideline recommendations and day to day clinical practice in navigating treatment options during lactation. Current guidelines indicate that methimazole at doses up to 20 mg per day can be used safely during breastfeeding. We report a 32‑year‑old woman with long‑standing Graves’ disease who experienced biochemical and clinical relapse two months postpartum, after discontinuing antithyroid therapy. At presentation, she was still breastfeeding her 9 month old infant. Hyperthyroidism was confirmed by markedly elevated free thyroxine and suppressed thyroid‑stimulating hormone, in the context of diffuse goiter and prior ophthalmopathy, findings consistent with postpartum Graves’ relapse rather than postpartum thyroiditis. Methimazole was reintroduced and titrated to 20 mg/day, with subsequent improvement in maternal symptoms and thyroid function, while breastfeeding was continued without clinical evidence of impaired growth or neurodevelopment in the infant. This case illustrates that methimazole at a daily dose of 20 mg can provide effective control of postpartum Graves’ hyperthyroidism without necessitating interruption of breastfeeding, in line with international recommendations that classify low to moderate doses of MMI as safe during lactation. Careful monitoring of maternal thyroid status and individualized counselling are essential to balance disease control with maintenance of lactation.