Antithyroid Drug Use in Pregnancy and Birth Defects: Why Some Studies Find Clear Associations, and Some Studies Report None.

@article{Laurberg2015AntithyroidDU,
  title={Antithyroid Drug Use in Pregnancy and Birth Defects: Why Some Studies Find Clear Associations, and Some Studies Report None.},
  author={Peter Laurberg and Stine Linding Andersen},
  journal={Thyroid : official journal of the American Thyroid Association},
  year={2015},
  volume={25 11},
  pages={
          1185-90
        }
}
BACKGROUND Rare cases of birth defects after the use of methimazole (MMI) or carbimazole to treat hyperthyroidism in early pregnancy have been reported since 1972, whereas propylthiouracil (PTU) has not been considered teratogenic. Recently, two studies reported birth defects after the use of MMI in early pregnancy to affect 2-4% of exposed children, and one study also found birth defects after the use of PTU. On the other hand, some published studies did not find associations between the use… 

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Birth defects after use of antithyroid drugs in early pregnancy: a Swedish nationwide study.

MMI and PTU were associated with subtypes of birth defects previously reported, but the frequency of ATD exposure in early pregnancy was low and severe malformations described in the MMI embryopathy were rarely observed.

Antithyroid drugs and birth defects

Current evidence corroborates a risk of birth defects associated with MMI while more evidence is needed to determine the teratogenic potential of PTU, and detailed assessment of type and timing of exposure in large cohorts are needed.

Effects of methimazole and propylthiouracil exposure during pregnancy on the risk of neonatal congenital malformations: A meta-analysis

For pregnant women with hyperthyroidism, exposure to MMI/CMZ significantly increased the incidence of neonatal congenital malformations compared to exposure to PTU and no antithyroid drug exposure; however, no differences were observed between PTU exposure and no anticancer drug exposure.

Maternal thyroid function, use of antithyroid drugs in early pregnancy and birth defects.

Results corroborate an increased risk of birth defects associated with the use of ATD in early pregnancy, and suggest that abnormal maternal thyroid function is not a major risk factor for birth defects.

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Current guidelines highlight the need for clinical attention on the use of ATDs in early pregnancy, but if the risk of relapse or worsening of hyperthyroidism is considered low, it is suggested that ATD treatment can be withdrawn followed by frequent monitoring of thyroid function.

Treatment of Graves’ hyperthyroidism with thionamides: a position paper on indications and safety in pregnancy

Data available on the effect ofhyperthyroidism per se on the risk of fetal malformations, although scanty, are sufficient to recommend treatment with ATD of the hyperthyroid pregnant woman, and recommendations derived form the available data and published guidelines of International Scientific Societies are edited.

Hyperthyroidism in Pregnancy: The Delicate Balance between Too Much or Too Little Antithyroid Drug

In hyperthyroid women with long-term ATD treatment before conception, drugs could be withdrawn in T1 in 40% of them, the thyroid function control was better, and pregnancy and fetal complications were rarer, compared to women diagnosed during pregnancy.

Thyroid Medication Use and Birth Defects in the National Birth Defects Prevention Study.

BACKGROUND Thyroid disorders are common among reproductive-aged women, with hypothyroidism affecting 2 to 3% of pregnancies, and hyperthyroidism affecting an additional 0.1 to 1%. We examined

Graves’ disease: developments in first-line antithyroid drugs in the young

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