This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Momotani, N. Articles by Ito, K. Search for Related Content PubMed PubMed Citation Articles by Momotani, N. Articles by Ito, K.

Effects of Propylthiouracil and Methimazole on Fetal Thyroid Status in Mothers with Graves’ Hyperthyroidism

Ito Hospital, 3–6 Jingumae, 4-Chome, Shibuya-Ku, 150 Tokyo, Japan

Address all correspondence and requests for reprints to: Naoko Momotani, M.D., Ito Hospital, 3–6 Jingumae, 4-Chome, Shibuya-Ku, 150 Tokyo, Japan.

Thionamide therapy is a mainstay of the treatment of hyperthyroidism complicated by pregnancy, but it can expose the fetus to hypothyroidism. In terms of fetal thyroid status, propylthiouracil (PTU) has been preferred over methimazole (MMI) based on experimental data on limited transplacental passage, and lower doses have been recommended. However, neither of these practices is supported by convincing clinical evidence.

We compared the effect of maternal ingestion of PTU with that of MMI on fetal thyroid status using cord sera at delivery in 77 mothers with Graves’ hyperthyroidism who were receiving thionamides and whose free T₄ (FT₄) levels were within the normal range. We also examined the dose effects on fetal thyroid status in these women. Thirty-four women were taking PTU (group P), and 43 were taking MMI (group M).

Neither the mean fetal FT₄ nor the mean fetal TSH level was significantly different between the two groups. No significant difference in the occurrence of low FT₄ levels or high fetal TSH levels was found between group P and group M (low FT₄, 6% vs. 7%; high TSH, 21% vs. 14%). Little relationship was observed between maternal doses and fetal thyroid status; in fact, when low doses of both PTU (100 mg daily or less) and MMI (10 mg daily or less) were administered, high TSH levels in the fetus were observed in 7 of the 34 fetuses (21%) and in 6 of the 43 fetuses (14%), respectively. Higher doses were associated with normal or low fetal TSH levels.

These findings demonstrate that in terms of fetal hypothyroidism-inducing potential, there is little reason to choose PTU over MMI. Individualized, not uniformly low, doses of these drugs may prevent fetal hypothyroidism.

This article has been cited by other articles:

				M. Inoue, N. Arata, G. Koren, and S. Ito Hyperthyroidism during pregnancy Can Fam Physician, July 1, 2009; 55(7): 701 - 703. [Abstract] [Full Text] [PDF]

				P. Laurberg, C. Bournaud, J. Karmisholt, and J. Orgiazzi Management of Graves' hyperthyroidism in pregnancy: focus on both maternal and foetal thyroid function, and caution against surgical thyroidectomy in pregnancy Eur. J. Endocrinol., January 1, 2009; 160(1): 1 - 8. [Abstract] [Full Text] [PDF]

				J. Girling Thyroid disease in pregnancy Obstet Gynaecol (Lond), October 1, 2008; 10(4): 237 - 243. [Abstract] [Full Text] [PDF]

				Subsection Reports J. Clin. Endocrinol. Metab., August 1, 2007; 92(8_suppl): s8 - s47. [Full Text] [PDF]

				M. Abalovich, N. Amino, L. A. Barbour, R. H. Cobin, L. J. De Groot, D. Glinoer, S. J. Mandel, and A. Stagnaro-Green Management of Thyroid Dysfunction during Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline J. Clin. Endocrinol. Metab., August 1, 2007; 92(8_suppl): s1 - s47. [Abstract] [Full Text] [PDF]

				J. M Chattaway and T. B Klepser Propylthiouracil Versus Methimazole in Treatment of Graves' Disease During Pregnancy Ann. Pharmacother., June 1, 2007; 41(6): 1018 - 1022. [Abstract] [Full Text] [PDF]

				E. N Pearce Diagnosis and management of thyrotoxicosis. BMJ, June 10, 2006; 332(7554): 1369 - 1373. [Full Text] [PDF]

				D. Luton, I. Le Gac, E. Vuillard, M. Castanet, J. Guibourdenche, M. Noel, M.-E. Toubert, J. Leger, C. Boissinot, M.-H. Schlageter, et al. Management of Graves' Disease during Pregnancy: The Key Role of Fetal Thyroid Gland Monitoring J. Clin. Endocrinol. Metab., November 1, 2005; 90(11): 6093 - 6098. [Abstract] [Full Text] [PDF]

				D. S. Cooper Antithyroid Drugs N. Engl. J. Med., March 3, 2005; 352(9): 905 - 917. [Full Text] [PDF]

				P. A. Waltman, J. M. Brewer, and S. Lobert Thyroid Storm During Pregnancy: A Medical Emergency Crit. Care Nurse, April 1, 2004; 24(2): 74 - 79. [Full Text] [PDF]

				M. J. E. Kempers, D. A. van Tijn, A. S. P. van Trotsenburg, J. J. M. de Vijlder, B. M. Wiedijk, and T. Vulsma Central Congenital Hypothyroidism due to Gestational Hyperthyroidism: Detection Where Prevention Failed J. Clin. Endocrinol. Metab., December 1, 2003; 88(12): 5851 - 5857. [Abstract] [Full Text] [PDF]

				P. K. Singh, C. A. Parvin, and A. M. Gronowski Establishment of Reference Intervals for Markers of Fetal Thyroid Status in Amniotic Fluid J. Clin. Endocrinol. Metab., September 1, 2003; 88(9): 4175 - 4179. [Abstract] [Full Text] [PDF]

				J. E. Polifka and J.M. Friedman Medical genetics: 1. Clinical teratology in the age of genomics Can. Med. Assoc. J., August 1, 2002; 167(3): 265 - 273. [Abstract] [Full Text] [PDF]

				S. J. Mandel and D. S. Cooper The Use of Antithyroid Drugs in Pregnancy and Lactation J. Clin. Endocrinol. Metab., June 1, 2001; 86(6): 2354 - 2359. [Full Text] [PDF]

				A. P. Weetman Graves' Disease N. Engl. J. Med., October 26, 2000; 343(17): 1236 - 1248. [Full Text] [PDF]

				B. Buckingham The Hyperthyroid Fetus and Infant NeoReviews, June 1, 2000; 1(6): e103 - 109. [Full Text]