ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2011) 25 P314

Carbimazole embryopathy: implications for the choice of antithyroid drugs in pregnancy

Pamela Bowman, Nigel Osborne, Rachel Sturley & Bijay Vaidya


Royal Devon and Exeter Hospital, Exeter, UK.


Background: Maternal thyrotoxicosis affects 0.2% of pregnancies. Pharmacological treatments include carbimazole, methimazole and propylthiouracil. The Endocrine Society recommends the use of propylthiouracil as first line during pregnancy, because of possible associations between carbimazole and congenital anomalies. However, recent reports link propylthiouracil to liver injury in adults, children, pregnant women and fetuses, raising questions over its safety.

Case: Our case is a 1-year-old girl who was exposed to carbimazole in utero due to treatment of maternal Graves’ disease. At conception her mother was taking 40 mg carbimazole with 100 μg thyroxine. On discovering she was pregnant, the thyroxine was stopped and the carbimazole gradually reduced to 10 mg for the remainder of the pregnancy. The mother remained euthyroid. The baby was born at 38 weeks gestation by forceps delivery. Birth weight was within the normal range at 2.78 kg. She was noted to have an atypical umbilical stump which was identified as a patent vitellointestinal duct. This was surgically repaired at the age of 5 months. She also had a scalp defect consistent with aplasia cutis, characteristic facial features (large forehead, broad flat nasal bridge and thin upper lip) and persistent upper airway noise due to laryngomalacia. Further investigations excluded oesophageal atresia, tracheo-oesophageal fistula and choanal atresia.

Evidence: A review of English publications in Medline revealed 31 other cases of 2 or more congenital anomalies reported in babies born to mothers treated with carbimazole or methimazole in pregnancy. Anomalies in these cases include distinctive facial features (68%), choanal atresia (65%), aplasia cutis (29%), nipple deformities (23%) developmental delay (16%), patent vitellointestinal duct (16%), tracheo-oesophageal fistula (13%), oesophageal atresia (13%) and omphalocele (6%).

Conclusion: Constellation of several congenital anomalies in our case and others supports the concept of a carbimazole embryopathy and the Endocrine Society advice to avoid carbimazole during the first trimester.

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