Graves disease occurs in 0.2-0.4% of all pregnancies(1). TSH receptor antibodies (TRABs) can persist despite definitive treatment, with presence of TRABs in up to 40% of patients 5 years post thyroid ablation(2). Guidelines recommend monitoring of TRAB titre if levels exceed three time the upper limit of normal during gestation as these levels have been shown to confer higher risk of neonatal thyrotoxicosis(3).
We present a case of fetal thyroxicosis in a 38 year old woman with a history of severe relapsing Graves’s hyperthyroidism complicated by ongoing opthalmopathy. Radioactive iodine treatment 20 years prior rendered her hypothyroid requiring thyroxine replacement. Two previous pregnancies were complicated with marked TRAB elevation(>20IU/L) and subsequent fetal thyrotoxicosis necessitating emergency caesarean sections at 35 and 36 weeks gestation. Both neonates were treated with carbimazole during the first weeks of life. In her 3rd pregnancy she was monitored from 10 weeks gestation with regular TRAB levels. CTG traces at 34 weeks gestation showed persistent fetal tachycardia of 200bpm, without of features of thyrotoxicosis on ultrasound. Carbimazole 10mg twice daily and propranolol 20mg twice daily was commenced, with the beta-blocker dosage being titrated against the CTG fetal heart rate. The fetal tachycardia resolved on treatment but by 36 weeks gestation ultrasound showed growth restriction, with the estimated fetal weight dropping from 65th to 35th centile, and associated oligohydramnios. The patient underwent an elective caesarean at 37 weeks. Biochemical neonatal thyrotoxicosis progressively worsened to day 3 post delivery (Table 1) consistent with reduced neonatal serum carbimazole concentration but ongoing TRAB activity (see table 1). Antithyroid drugs (ATDs) cross the placenta(4) and neonatal thyrotoxicosis may not become apparent until 2-5 days post birth when ATDs are cleared from the circulation. The neonate was commenced on carbimazole with good biochemical and clinical effect. This case demonstrates the need for recognition of TRAB status in women with definitively treated Graves’ disease as fetal hyperthyroidism may occur despite maternal euthyroidism (5).