Carbimazole, Thiamazole (Methimazole)

Exposed non-exposed studies (cohort)

Study Country
Study period
Population source Exposure definition Non-exposure definition Sample size Rmk
Andersen (control exposed to PTU), 2019 Denmark
1997 - 2016
All children live-born in Denmark from January 1, 1997 to December 31, 2016 who were identified in the Danish Medical Birth Register (MBR) and had available information on gestational age at birth. Use of MMI/CMZ in early pregnancy (redeemed prescriptions of the drugs in the period ranging from six months prior to pregnancy start up to and including the 10th week of pregnancy) exposed to other treatment, sick
Use of PTU in early pregnancy (redeemed prescriptions of the drugs in the period ranging from six months prior to pregnancy start up to and including the 10th week of pregnancy)
1574 / 889 Update of the previous study Andersen 2013 '(children born from 1996 to 2008) with this longer study (1997-2016).
Andersen (control unexposed, disease free), 2019 Denmark
1997 - 2016
All children live-born in Denmark from January 1, 1997 to December 31, 2016 who were identified in the Danish Medical Birth Register (MBR) and had available information on gestational age at birth. Use of MMI/CMZ in early pregnancy (redeemed prescriptions of the drugs in the period ranging from six months prior to pregnancy start up to and including the 10th week of pregnancy) unexposed, disease free
Children whose mother had no diagnosis of hyperthyroidism, no registration of thyroid surgery and no redeemed prescription of ATD or Levothyroxine before, during or after the pregnancy under study and up to December 31, 2017
1574 / 1159181 Update of the previous study Andersen 2013 '(children born from 1996 to 2008) with this longer study (1997-2016).
Andersen 2014 (control unexposed, disease free), 2014 Denmark
1996 - 2008
All children live-born from 1996 to 2008 Live-born children exposed to MMI/CMZ in early pregnancy unexposed, disease free
Children born to mothers with no prescriptions of ATD and/or thyroid hormones redeemed 1995 to 2008 and no diagnosis of hyperthyroidism in the DNHR from 1977 to 2008.
1097 / 811730 This study is a extension (focused on subtype of congenital heart defect) of the study previously published (Andersen et al. 2013), using methods previously described in detail. Therefore, methods are extracted from the article Andersen et al. 2013.
Andersen 2017 (control exposed to PTU), 2017 Sweden
2006 - 2012
All live-born children in Sweden between 2006 and 2012 The child was defined as exposed to MMI/CMZ in early pregnancy if the mother had at least one redeemed prescription of ATD less than six months before the estimated pregnancy start and before the 11th gestational week. exposed to other treatment, sick
Children born to mothers who were treated with PTU in early pregnancy if the mother had at least one redeemed prescription of ATD less than six months before the estimated pregnancy start and before the 11th gestational week.
162 / 218 Subanalyze of live-born children exposed to MMI/CMZ (n = 162) in early pregnancy versus PTU. The study also analyzed live-born children exposed to PTU (n = 218), to MMI/CMZ and PTU (n= 66) in early pregnancy. TOTAL : n =446.
Andersen 2017 (control unexposed, disease free), 2017 Sweden
2006 - 2012
All live-born children in Sweden between 2006 and 2012 The child was defined as exposed to MMI/CMZ in early pregnancy if the mother had at least one redeemed prescription of ATD less than six months before the estimated pregnancy start and before the 11th gestational week. unexposed, disease free
Children born to mothers with no redeemed prescriptions of ATD or thyroid hormones from 2005 to 2014 and no diagnosis of hyperthyroidism registered from 2005 to 2014 in the Swedish National Patient Register.
162 / 682343 Subanalyze of live-born children exposed to MMI/CMZ (n = 162) in early pregnancy. The study also analyzed live-born children exposed to PTU (n = 218), to MMI/CMZ and PTU (n= 66) in early pregnancy. TOTAL : n =446.
Andersen 2017 (control unexposed, sick), 2017 Sweden
2006 - 2012
All live-born children in Sweden between 2006 and 2012 The child was defined as exposed to MMI/CMZ in early pregnancy if the mother had at least one redeemed prescription of ATD less than six months before the estimated pregnancy start and before the 11th gestational week. unexposed, sick
Children born to mothers who were treated with ATD more than one year before or more than one year after pregnancy and received no treatment with thyroid hormone in pregnancy.
162 / 1551 Subanalyze of live-born children exposed to MMI/CMZ (n = 162) in early pregnancy. The study also analyzed live-born children exposed to PTU (n = 218), to MMI/CMZ and PTU (n= 66) in early pregnancy. TOTAL : n =446.
Azizi, 2002 Iran
Not specified
Not clearly specified. Women with thyrotoxicosis who received methimazole (MMI) therapy during pregnancy, but not during lactation. unexposed (not otherwise specified)
Not exposed to methimazole (MMI) therapy during pregnancy (illness status not specified).
23 / 30
Chen (control exposed to PTU), 2011 Taiwan
Jan 2005 - Dec 2005
All women in Taiwan who had live singleton births and used prenatal care services from 1 January 2005 to 31 December 2005 Women with hyperthyroidism diagnosis, who were prescribed MMI treatment during pregnancy for more than 30 days during pregnancy. exposed to other treatment, sick
Women with hyperthyroidism diagnosis, who were prescribed PTU treatment during pregnancy for more than 30 days during pregnancy.
73 / 630 Subanalyze of live-born children exposed to MMI/CMZ (n = 73) during pregnancy. The study also analyzed live-born children exposed to PTU (n = 630) ; to MMI/CMZ or PTU (n= 703) during pregnancy.
Chen (control unexposed, disease free), 2011 Taiwan
Jan 2005 - Dec 2005
All women in Taiwan who had live singleton births and used prenatal care services from 1 January 2005 to 31 December 2005 Women with hyperthyroidism diagnosis, who were prescribed MMI treatment during pregnancy for more than 30 days during pregnancy. unexposed, disease free
The remaining women in the database, excluding women with a diagnosis of hyperthyroidism anytime during the period 1996-2006.
73 / 14150 Subanalyze of live-born children exposed to MMI/CMZ (n = 73) during pregnancy. The study also analyzed live-born children exposed to PTU (n = 630) ; to MMI/CMZ or PTU (n= 703) during pregnancy.
Chen (control unexposed, sick), 2011 Taiwan
Jan 2005 - Dec 2005
All women in Taiwan who had live singleton births and used prenatal care services from 1 January 2005 to 31 December 2005 Women with hyperthyroidism diagnosis, who were prescribed MMI treatment during pregnancy for more than 30 days during pregnancy. unexposed, sick
Women with a diagnosis of hyperthyroidism not receiving antithyroid drug.
73 / 2127 Subanalyze of live-born children exposed to MMI/CMZ (n = 73) during pregnancy. The study also analyzed live-born children exposed to PTU (n = 630) ; to MMI/CMZ or PTU (n= 703) during pregnancy.
Di Gianantonio, 2001 France, Germany, Israel, Italy, The Netherlands
Not specified
Pregnant women who were referred to the TIS units for risk assessment. Pregnant women exposed to MMI during the preconceptional period and/or the first trimester to treat hyperthyroidism. unexposed, disease free
Pregnant women exposed to nonteratogenic drugs during the preconceptional period and/or the first trimester
241 / 1089
Dwarakanath (control exposed to PTU), 1999 India
Not specified
Women with Graves' disease who conceived while undergoing treatment at the Endocrine Clinic of the hospital Women with Graves' disease exposed to methimazole/neomercazole during pregnancy exposed to other treatment, sick
Women with Graves' disease exposed to propylthiouracil during pregnancy
8 / 8
Gianetti (control exposed to PTU), 2015 Italy
1992 - 2005
Pregnant women affected by thyroid diseases and followed in eight Italian Departments of Endocrinology around Italy. Pregnancies of women being treated with MMI for Graves’ disease (GD) or toxic nodular goiter (TNG). exposed to other treatment, sick
Pregnancies of women being treated with PTU for Graves’ disease (GD) or toxic nodular goiter (TNG).
124 / 52 Addition of the 2 groups of pregnancies exposed to MMI (euthyroid and hyperthyroid) and also for PTU. All patients included in the study received their diagnosis and started their therapies at least 3 months before pregnancy.
Gianetti (control unexposed, sick), 2015 Italy
1992 - 2005
Pregnant women affected by thyroid diseases and followed in eight Italian Departments of Endocrinology around Italy. Pregnancies of women being treated with MMI for Graves’ disease (GD) or toxic nodular goiter (TNG). unexposed, sick
Pregnant women who were affected by thyroid diseases but were euthyroid (either on LT4 therapy for hypothyroidism or without treatment) and did not receive any ATD medication during pregnancy.
124 / 203 Addition of the 2 groups of pregnancies exposed to MMI (euthyroid and hyperthyroid at least twice during pregnancy). All patients included in the study received their diagnosis and started their therapies at least 3 months before pregnancy.
Hawken (control exposed to PTU), 2016 France
2005 - 2012
Pegnant women with Graves' disease (progressive or not), treated with Synthetic antithyroid drugs (SAT) and/or surgery and/or RAI therapy, discovered before or during pregnancy and followed by a hospital or open-care endocrinologist in the Poitou-Charentes region. Foetuses exposed to carbimazole (CMZ) during pregnancy. exposed to other treatment, sick
Foetuses exposed to propylthiouracil (PTU) during pregnancy.
19 / 13 Treatment of Graves’ disease diagnosed during pregnancy (14 patients) : - 6 PTU en T1 => 0 malfo - 2 CMZ en T1 => 1 malfo Treatments in patients under SAT at the time of starting pregnancy (24 patients). - 7 PTU en T1 => 0 malfo - 17 CMZ en T1 => 3 malfo
Korelitz (control exposed to PTU), 2013 USA
2005 - 2009
Women aged 15–44 years who were enrolled for at least 24 months with prescription drug benefits and had at least two pregnancy-related medical service claims between 2005 and 2009 Antithyroid (MMI only) drug use within 6 months before the pregnancy start date or during pregnancy exposed to other treatment, sick
Antithyroid (PTU only) drug use within 6 months before the pregnancy start date or during pregnancy
108 / 915
Korelitz (control unexposed, disease free), 2013 USA
2005 - 2009
Women aged 15–44 years who were enrolled for at least 24 months with prescription drug benefits and had at least two pregnancy-related medical service claims between 2005 and 2009 Antithyroid (MMI only) drug use within 6 months before the pregnancy start date or during pregnancy. unexposed, disease free
No Antithyroid (MMI or PTU) drug use in women without thyrotoxicosis.
108 / 634858
Korelitz (control unexposed, sick), 2013 USA
2005 - 2009
Women aged 15–44 years who were enrolled for at least 24 months with prescription drug benefits and had at least two pregnancy-related medical service claims between 2005 and 2009 Antithyroid (MMI only) drug use within 6 months before the pregnancy start date or during pregnancy. unexposed, sick
No Antithyroid (MMI or PTU) drug use in women with thyrotoxicosis before/during pregnancy.
108 / 3236
Lo (control exposed to PTU), 2015 USA
1996 - 2010
All pregnancies resulting in a live birth during the study period among women age 15–49 years at the time of delivery Pregnant women with a maternal diagnosis of thyrotoxicosis and treated with MMI only during pregnancy. exposed to other treatment, sick
Pregnant women with a maternal diagnosis of thyrotoxicosis and treated with PTU only during pregnancy.
30 / 507
Lo (control unexposed, sick), 2015 USA
1996 - 2010
All pregnancies resulting in a live birth during the study period among women age 15–49 years at the time of delivery Pregnant women with a maternal diagnosis of thyrotoxicosis and treated with MMI only during pregnancy. unexposed, sick
Pregnant women with a maternal diagnosis of thyrotoxicosis and with no ATD and no thyroid hormone during pregnancy.
30 / 1171
McCarroll (Buckinghamshire control group), 1976 Ireland
1960 - 1971
Not clearly defined. Children born to carbimazole-treated thyrotoxic women. unexposed, disease free
Original Buckinghamshire group
25 / 6160
McCarroll (Northern Ireland control group), 1976 Ireland
1960 - 1971
Children born to carbimazole-treated thyrotoxic women. unexposed, disease free
Northern Ireland boys and girls obtained from medical inspections made in 1972.
25 / 20
Momotani, 1984 Japan
1965 - 1980
Infants born alive between August 1965 and May 1980 to mothers who were seen at Ito Thyroid Clinic and Hospital and diagnosed as having Graves’ disease. Infants whose mothers were treated with MMI during 1st trimester and were hyperthyroid or euthyroid. unexposed, sick
Infants whose mothers were not treated with MMI during 1st trimester and were hyperthyroid or euthyroid.
243 / 400 Treated group: addition of « Treated, hyperthyroid » and « Treated, euthyroid ». Unexposed: addition of « Untreated, hyperthyroid » and « Untreated, euthyroid ».
Momotani (control exposed to PTU), 1997 Japan
Not specified
Pregnant women with Graves’ disease Pregnant women with Graves’ disease who continued methimazole (MMI) until delivery. exposed to other treatment, sick
Pregnant women with Graves’ disease who continued propylthiouracil (PTU) until delivery.
43 / 34 34 were treated with PTU (group P), and 43 were treated with MMI (group M)
Seo (control exposed to PTU), 2018 Korea
2008 - 2014
About all live-born infants (90.0% of nationwide live births during the period). At least one maternal prescription of MMI alone during the first trimester. exposed to other treatment, sick
At least one maternal prescription of PTU alone during the first trimester.
1120 / 9930 3 types of ATD exposure: PTU alone (n = 9930), MMI alone (n = 1120), and both PTU and MMI (n = 1841). 210 cases of carbimazole use were included in the MMI groups
Seo (control unexposed, NOS), 2018 Korea
2008 - 2014
About all live-born infants (90.0% of nationwide live births during the period). At least one maternal prescription of MMI during the first trimester. unexposed (not otherwise specified)
Women who had no prescription claims for Antithyroid drugs (ATDs) from the beginning of pregnancy to the day before childbirth.
1120 / 2872109 3 types of ATD exposure: PTU alone (n = 9930), MMI alone (n = 1120), and both PTU and MMI (n = 1841). 210 cases of carbimazole use were included in the MMI groups
Wing (control exposed to PTU), 1994 USA
1974 - 1990
Patients with a history or diagnosis of hyperthyroidism evaluated in our high-risk obstetrics clinic between July 1974 and June 1990. The patients were followed up prospectively during pregnancy. Pregnant women who were diagnosed with or had a history of hyperthyroidism treated with methimazole only during pregnancy. exposed to other treatment, sick
Pregnant women who were diagnosed with or had a history of hyperthyroidism treated with propylthiouracil only during pregnancy.
36 / 99 A cohort was established to compare the outcome of patients treated with propylthiouracil and methimazole.
Wing (control unexposed, sick), 1994 USA
1974 - 1990
Patients with a history or diagnosis of hyperthyroidism evaluated in our high-risk obstetrics clinic between July 1974 and June 1990. The patients were followed up prospectively during pregnancy. Pregnant women who were diagnosed with or had a history of hyperthyroidism treated with methimazole only during pregnancy. unexposed, sick
Patients who were either euthyroid throughout pregnancy and required no medications or were hyperthyroid but were seen late in pregnancy.
36 / 43 A cohort was established to compare the outcome of patients treated with propylthiouracil and methimazole.
Yoshihara (control exposed to PTU), 2012 Japan
1999 - 2010
Women with Graves’ disease who became pregnant during the study period. Mothers who received MMI for the treatment of Graves’ disease in the first trimester of pregnancy (0 –12 wk gestation). exposed to other treatment, sick
Mothers who received PTU for the treatment of Graves’ disease in the first trimester of pregnancy (0 –12 wk gestation).
1426 / 1578 Compare the proportions of infants born with congenital malformations to mothers in the groups treated with each of the antithyroid drugs and to the mothers who were not treated with any antithyroid drugs during the first trimester of pregnancy.
Yoshihara (control unexposed, sick), 2012 Japan
1999 - 2010
Women with Graves’ disease who became pregnant during the study period. Mothers who received MMI for the treatment of Graves’ disease in the first trimester of pregnancy (0 –12 wk gestation). unexposed, sick
Mothers who received no medication for the treatment of Graves’ disease during the first trimester of pregnancy (0 –12 wk gestation).
1426 / 2065 Compare the proportions of infants born with congenital malformations to mothers in the groups treated with each of the antithyroid drugs and to the mothers who were not treated with any antithyroid drugs during the first trimester of pregnancy.

Case-control studies (cohort)

Study Country
Study period
Case Control Sample size Rmk
Banhidy, 2011 Hungary
1980 – 1996
Fetus/infants affected with major Congenital anomaly, selected from the data set of the Hungarian Congenital Abnormality Registry (HCAR), born of mother with hyperthyroidism. Newborn infants without any Congenital anomaly, selected from the National Birth Registry of the Central Statistical Office for the HCCSCA, born of mother with hyperthyroidism. 71 / 116 Of 71 case mothers, four (5.6%), while of 116 control mothers, eight (6.9%) were treated with antithyroid drugs.
Barbero, 2008 Argentina
1976 - 2006
Patients with unilateral or bilateral choanal atresia who received surgical treatment during the period 1976–2006. Children without choanal atresia but treated at the same centers because of other respiratory diseases 61 / 183 Non exposed women had mainly not reported hyperthyroidism (only in 2 (2/183) controls’ mothers).
Clementi, 2010 International (twelve surveillance programs)
Not specified
Cases with the specific malformation being tested and reported first-trimester exposure to medication. Cases with any other malformation and reported first-trimester exposure to medication. -9 / -9 “exposed case-only” design: all infants had a major birth defect and were exposed to some medication. TOTAL: 18131 cases with malformations and reported first-trimester exposure to medication.
Khoury, 1989 USA
1981 - 1983
Stillborn and liveborn babies with birth defects (cases were classified into 66 broad and specific birth defect groups) A random sample of babies without birth defects, frequency-matched to cases by race, hospital of birth, and period of birth. 4904 / 3027

See the method used to produce these results