Propylthiouracil (PTU) treatment for thyrotoxicosis in pregnancy is common clinical practice. However maternal ingestion of PTU has been recognised to be associated with the development of foetal hypothyroidism and in rare cases at high doses of PTU, overt foetal goitre. Foetal goitre can be potentially dangerous due to mechanical obstruction and needs to be carefully monitored in utero. We report a case of development of goitre in utero secondary to maternal ingestion of PTU during pregnancy.
Case report: A 31-year-old lady presented with thyrotoxicosis in her first pregnancy at 8 weeks gestation with TSH 0.56 mu/L (0.24.0), free T4 46.2 pmol/L (12.04.0) and total T3 3.7 nmol/L (1.12.6). Maternal thyroid peroxidase antibodies were negative. There was no known family history of thyroid disorder. Treatment with PTU was initiated at 200 mg bd resulting in euthyroidism at 24 weeks gestation with TSH 1.32 mu/L, free T4 11.4 pmol/L and total T3 1.8 nmol/L and PTU was gradually reduced to 100 mg daily. However ultrasounds scan (USS) at 29 weeks gestation revealed foetal goitre measuring 33×26 mm and polyhydramnios. PTU was promptly stopped. At 30 weeks gestation foetal blood sampling via cordocentesis showed normal foetal TSH and free T4. Serial US scans revealed progressive reduction of goitre and polyhydramnios with normal foetal growth until normalisation at 34 weeks gestation. MRI scan of the foetus at 35 weeks was within normal limit. Maternal euthyroid status was maintained throughout pregnancy and baby was safely delivered at term. At 4 weeks post partum both mother and baby remained euthyroid with maternal TSH 0.74 mu/L and free T4 16.0 pmol/L.
This case emphasises the importance of regular monitoring for the development of foetal goitre in pregnant women on PTU in the second and third trimesters of pregnancy. We suggest that this should be the standard practice.