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Practice Pregnancy Plus

Hyperthyroidism and pregnancy

BMJ 2008; 336 doi: (Published 20 March 2008) Cite this as: BMJ 2008;336:663

This article has a correction. Please see:

  1. Helen Marx, registrar in obstetrics and gynaecology 1,
  2. Pina Amin, consultant obstetrician 2,
  3. John H Lazarus, professor of clinical endocrinology, and honorary consultant physician 1
  1. 1Department of Obstetrics, University Hospital of Wales, Cardiff CF14 4XN
  2. 2Centre for Endocrine and Diabetes Sciences, University Hospital of Wales, Cardiff
  1. Correspondence to: J H Lazarus lazarus{at}

Pregnant women with hyperthyroidism need careful management as some may be at increased risk of fetal loss, pre-eclampsia, heart failure, premature labour, and having a low birthweight baby

Various problems may arise in the management of a pregnant patient with hyperthyroidism (see scenario box).1 This article will explore the problems in relation to the prevalence of hyperthyroidism in pregnancy, therapeutic issues, pregnancy planning, and clinical management. No controlled trials of management have been conducted, but consensus guidelines have recently been published.2


A 35 year old woman develops Graves’ hyperthyroidism (the commonest cause of hyperthyroidism) four months after the birth of her second child. She receives treatment with antithyroid drugs for six months. In her third pregnancy she complains of palpitations, excessive sweating, and heat intolerance at 16 weeks’ gestation. Although she experienced these symptoms in previous pregnancies, the current symptoms are much worse.

She is found to be severely hyperthyroid, with raised concentrations of serum free thyroxine (51.7 pmol/l (normal range 9.8-23.1 pmol/l) and free triiodothyronine (19.9 pmol/l (3.5-6.5 pmol/l)) and with suppressed concentrations of thyrotrophin (thyroid stimulating hormone) (<0.02 mU/l (0.35-5.5 mU/l)). She is treated with propylthiouracil, initially 150 mg three times daily, which is reduced eventually to 50 mg twice daily as she becomes euthyroid. Thyrotrophin receptor antibodies are measured at 30 weeks’ gestation and are negative. Propylthiouracil is continued throughout pregnancy and she breast feeds while taking the drug. The drug is stopped two months postpartum; thyroid function is normal three weeks later.

How common is hyperthyroidism in pregnancy?

Hyperthyroidism occurs in 2/1000 pregnancies in the United Kingdom.3 Graves’ hyperthyroidism (defined as hyperthyroidism that is the result of stimulation of the thyroid by thyrotrophin receptor stimulating antibodies (TRAb)) is the commonest cause of hyperthyroidism in young women (about 85% of cases) in the United Kingdom.1 The prevalence of undiagnosed …

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