Endocrine Abstracts (2018) 55 OC6 | DOI: 10.1530/endoabs.55.OC6

Management of T3-toxicosis in pregnancy

Ruth Cordiner1, David Carty1,2, Andrew Powls3, Fiona Mackenzie3, Avril Scott3, Janice Gibson4 & Robert Lindsay1,2

1Glasgow Royal Infirmary, Glasgow, UK; 2University of Glasgow, Glasgow, UK; 3Princess Royal Maternity Hospital, Glasgow, UK; 4Queen Elizabeth University Hospital, Glasgow, UK.

Case history: Pre pregnancy: A 31-year-old female with no family history of thyroid disease presented with clinical hyperthyroidism and large goitre with bruit. Graves’ Disease was confirmed: TSH <0.01 (0.35–5.0 mU/l), free T4 53.4 (9.0–21.0 pmol/l), TSH Receptor Antibodies (TRAB) >40 (0–1.9 U/l), TPO 32.2 (<6 U/ml). She started on carbimazole (CBZ: 20 mg BD) and propranolol. She then switched to propylthiouracil (PTU: 150 mg BD) at 2 months due to desire for future pregnancy. US thyroid showed a >5 cm, hyper-vascular lobulated goitre.

First trimester: Booked to obstetric/endocrine clinic at 7–8 weeks’ gestation, four months after original presentation. Booking bloods: T4 (fT4 7.1 pmol/l), Total T3 >12.3 nmol/l, TSH <0.01 mU/l). Due to low T4 in very early pregnancy, PTU and propranolol were continued but T4 considered, then eventually added, to maintain the mothers T4.

Second trimester: Mother continued anti-thyroid medication (PTU then CBZ) with supressed TSH, raised T3 and clinically improved but ongoing signs of thyrotoxicosis. Foetal thyroid scanning was commenced at 18 weeks. Foetal goitre (>95th centile) was seen from 21/40 with radiological evidence of thyrotoxicosis (central vascularization on Doppler) but normal foetal heart rate. Cordocentesis was offered but declined. In conjunction with obstetrics, CBZ was increased. Foetal goitre increased, therefore cordocentesis and foetal MRI were undertaken at 27/40. MRI confirmed a foetal goitre (right lobe 1.4 cm×1.2 cm, left lobe 1.4 cm×1.1 cm) with minor airway flattening. Cordocentesis suggested foetal hypothyroidism: TSH 36.45, fT4 9.8, total T3 0.3. Maternal CBZ was down-titrated to 5 mg with reduction in foetal goitre from 31/40; thyroid circumference <50th centile by 37/40. Foetal growth scans were normal throughout.

Delivery and postnatal: Maternal biochemistry at 39/40: TSH <0.01 mU/l, fT4 15.0 pmol/l, total T3 3.2 nmol/l, TRABs 3.7 U/l. Baby was delivered by uncomplicated SVD. Neonatal biochemistry was nominally euthyroid at birth but showed neonatal thyrotoxicosis at 5 days (TSH 0.31 mU/l, fT4 40.1 pmol/l, total T3 2.7 nmol/l, TRAB 6.1 U/l).

Conclusions and points for discussion: We describe a rare case of resistant T3 toxicosis in pregnancy. A number of discussion points include 1. Pre-pregnancy planning in women with Graves’ Disease, 2. Consideration of need for T4 supplementation when levels are low in T3 toxicosis in pregnancy, 3. Foetal monitoring with role of fetal ultrasound (for size and signs of hypo- and hyperthyroidism) and cordocentesis, 4. Neonatal thyrotoxicosis.

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