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Journal of Thyroid Research
Volume 2011, Article ID 235130, 5 pages
Research Article

Suspected Spontaneous Reports of Birth Defects in the UK Associated with the Use of Carbimazole and Propylthiouracil in Pregnancy

1Department of Paediatrics, Royal Devon and Exeter Hospital, Exeter, Devon EX25DW, UK
2Department of Endocrinology, Royal Devon and Exeter Hospital, Exeter, Devon EX25DW, UK
3Peninsula NIHR Clinical Research Facility, Level 2, Peninsula Medical School, University of Exeter, Barrack Road, Exeter, Devon EX25DW, UK

Received 19 April 2011; Revised 19 June 2011; Accepted 19 June 2011

Academic Editor: Kris Gustave Poppe

Copyright © 2011 Pamela Bowman and Bijay Vaidya. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The concept of a carbimazole embryopathy underlies current Endocrine Society advice to avoid this drug in early pregnancy, favouring propylthiouracil as an alternative for the treatment of maternal hyperthyroidism. We aimed to establish whether suspected spontaneous reporting of adverse drug reactions in the UK via the Yellow Card Scheme supports a carbimazole embryopathy and the lack of association between propylthiouracil and congenital anomalies. All birth defects related to maternal treatment with carbimazole or propylthiouracil reported over a 47-year period via the Yellow Card Scheme were analysed. 57 cases with 97 anomalies were reported following in utero exposure to carbimazole. These anomalies included aplasia cutis, choanal atresia, tracheo-oesophageal fistula, and patent vitellointestinal duct, which have previously been reported in association with carbimazole/methimazole exposure in utero. Only 6 cases with 11 anomalies were reported for propylthiouracil, all within the last 15 years. Therefore, these findings may support a carbimazole embryopathy. There are few birth defects associated with propylthiouracil, but this should be interpreted in the context of higher historical prescription rates for carbimazole.