FRI571 Maternal Graves’ Disease With Foetal Thyrotoxicosis And Goitre

Abstract Disclosure: D. Fennell: None. J. Walsh: None. M. Hatunic: None. Background: Graves’ disease (GD) is an uncommon condition affecting 0.2% of pregnancies. Foetal and neonatal thyrotoxicosis occurs in between 1-5% of pregnant patients with a history of GD, typically beyond 20 weeks gestation. Given its potential for serious morbidity and mortality, prompt recognition and treatment of the condition is essential. Clinical case: A 34-year-old female was referred at 21+2 weeks’ gestation from another hospital due to concerning cardiac findings noted on routine prenatal ultrasound (US). Her medical history was significant for GD (TRAb positive) with moderate ophthalmopathy and total thyroidectomy ten months prior, on L-thyroxine 150 mcg daily. Foetal tachycardia 170-180bpm was noted, with US showing with right ventricular hypertrophy, small pericardial effusion and a 1.9 x 2.7 x 2.8cm neck mass, suspicious for foetal goitre. Maternal laboratory studies showed TSH 2.38mIU/L (0.27-4.2), FT4 16.0pmol/L (12-22), TPO antibody negative <3.0IU/ml and TRAb markedly elevated >30IU/L (0-1.8). A diagnosis of foetal thyrotoxicosis secondary to placental passage of maternal TRAb was made. She was commenced on carbimazole 20mg twice daily at 21+6 weeks’ gestation as treatment, with the goal of normalising foetal heart rate. Careful, weekly follow-up with US scanning noted gradual improvement in the foetus’ condition, with resolution of pericardial effusion and foetal heart rate normalisation. Maternal TFTs were monitored weekly and she remained euthyroid on increased dose L-thyroxine (200 mcg daily). Multidisciplinary team consensus was to proceed with elective Caesarean section at 34 weeks’ gestation, to avoid risk of airway obstruction from foetal goitre. A healthy male infant was born with spontaneous breathing and normal heart rate at delivery. Apgar scores were 9 and 9 at 1 and 5 minutes. Maternal carbimazole was immediately discontinued post-delivery and L-thyroxine reduced to 150 mcg daily. She had an uncomplicated recovery post-Caesarean section. The infant was closely monitored in the neonatal ICU. On day five of life, he became unwell, developing a supraventricular tachycardia. Thyrotoxicosis was confirmed on laboratory studies (FT4 >100pmol/L). Carbimazole, propranolol and Lugol’s iodine were all used as treatment. Thyroid hormone levels normalised within days, with gradual clinical improvement. He was discharged home well four weeks after birth, remaining on propranolol 0.3mg four times daily and carbimazole 0.5mg twice daily, with close paediatric outpatient follow-up planned. Conclusion: Foetal thyrotoxicosis is a rare condition, but can cause serious morbidity, as demonstrated here. First trimester maternal thyroid antibody testing is recommended for all patients with a history of GD, to identify those at risk. Management of the condition is complex, requiring multidisciplinary specialist input for favourable outcome. Presentation: Friday, June 16, 2023