February 02, 2016
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Restrict antithyroid drugs early in pregnancy to reduce birth defect risk

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Restricting the use of antithyroid drugs in early pregnancy may reduce the risk for birth defects in the child, according to study findings published in The Journal of Clinical Endocrinology & Metabolism.

“For the use of [antithyroid drugs] in pregnant women, the dominating side effect is birth defects,” the researchers wrote. “The risk of agranulocytosis and liver failure should be kept in mind, but is less important.”

Stine Lindig Andersen

Stine Linding Andersen

Stine Linding Andersen, MD, and Peter Laurberg, professor, MD, of the departments of endocrinology and clinical biochemistry at Aalborg University Hospital in Denmark, and colleagues evaluated data from the Danish Medical Birth Register on 2,299,952 parents of a live-born child studied from 1995 to 2010 for the use of antithyroid drugs. A subanalysis of 830,680 live-born pregnancies from 1996 to 2008 was identified. Researchers sought to determine the frequency of birth defects associated with antithyroid drug therapy.

From 1995 to 2010, 28,998 people redeemed prescriptions for antithyroid drugs; methimazole/carbimazole was the most common prescription (n = 27,281), followed by propylthiouracil (n = 5,895) and both methimazole/carbimazole and propylthiouracil (n = 4,178). There were 45 cases of antithyroid drug-associated agranulocytosis and 10 cases of liver failure. Agranulocytosis was more common among participants treated with propylthiouracil compared with methimazole/carbimazole (P = .02). Rates of liver failure were similar between participants treated with methimazole/carbimazole and propylthiouracil. Most side effects developed within 3 months of initiation of antithyroid drug treatment.

Peter Laurberg

Peter Laurberg

Prescriptions of antithyroid drugs were redeemed in 2,115 pregnancies (methimazole/carbimazole, n = 1,347; propylthiouracil, n = 1,103; and methimazole/carbimazole and propylthiouracil, n = 335). There was one case of agranulocytosis and one case of liver failure in pregnancy. Overall, there were 75 birth children with birth defects linked to maternal use of antithyroid drugs during pregnancy.

“Untreated or undetected hyperthyroidism in women of reproductive age may seriously complicate a pregnancy, and should always be carefully managed and controlled,” Andersen told Endocrine Today. “An important take home message is that the early pregnancy period is just as important for the thyroid physician as the late pregnancy is for the obstetrician. Physicians treating young women with antithyroid drugs should be aware of the importance of a possible future pregnancy. It is mandatory to discuss with such women that pregnancy should be detected as early as possible. If pregnancy is detected, the responsible physician should be contacted immediately to consider the woman’s need for and type of antithyroid drug therapy in early pregnancy.” – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.