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Hyperthyroidism in Pregnancy

Distinguishing physiological hCG-mediated thyrotoxicosis from Graves disease in pregnancy.

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

References (5)

This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Kadın Hastalıkları ve Doğum department. Book Appointment →

What is Hyperthyroidism in Pregnancy?

Overt hyperthyroidism complicates 0.1-0.4% of pregnancies; transient gestational thyrotoxicosis (hCG-mediated) is more common but usually resolves by 18-20 weeks.

Graves disease accounts for 85-95% of pathological hyperthyroidism in pregnancy and is mediated by stimulating TSH-receptor antibodies that cross the placenta.

Untreated maternal hyperthyroidism increases the risk of preeclampsia, preterm birth, low birth weight, miscarriage, stillbirth, congestive heart failure and thyroid storm; fetal-neonatal hyperthyroidism may occur from transplacental antibody passage.

Symptoms

Maternal: tachycardia disproportionate to pregnancy, tremor, heat intolerance, insomnia, weight loss despite good appetite
Diffuse goitre and orbitopathy strongly suggest Graves disease
Severe nausea, vomiting and dehydration suggest gestational thyrotoxicosis with hyperemesis gravidarum
Laboratory: suppressed TSH (under 0.1 mU/L) with elevated free T4 and/or free T3
Positive TSH-receptor antibodies (TRAb) confirm Graves disease
Fetal: tachycardia over 160 bpm, growth restriction, goitre on ultrasound, accelerated bone maturation
Neonatal: irritability, poor weight gain, tachycardia, exophthalmos, goitre

Risk Factors

Personal or family history of autoimmune thyroid disease
Previous Graves disease in remission or treated with radioiodine or thyroidectomy (residual antibodies)
Type 1 diabetes mellitus and other autoimmune disorders
Multiple pregnancy or molar pregnancy (high hCG levels)
Hyperemesis gravidarum (transient gestational thyrotoxicosis)
Excess iodine intake or iodine-containing contrast media
Use of amiodarone or interferon

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Suppressed TSH with elevated free T4 in pregnancy needs urgent endocrinology referral
  • New-onset palpitations, tremor or weight loss during pregnancy warrants thyroid function testing
  • Known Graves disease patients planning pregnancy require pre-conception counselling and TRAb measurement
  • Severe symptoms (high fever, heart failure, altered mentation) suggest thyroid storm and require emergency admission
  • Fetal tachycardia, goitre or growth restriction in known Graves patients warrants maternal-fetal medicine review

Treatment Methods

01
Distinguish gestational thyrotoxicosis (resolves by week 18-20, no autoantibodies) from Graves disease (TRAb positive, persistent)
02
Gestational thyrotoxicosis: supportive care, hydration, beta-blockers if needed; antithyroid drugs not indicated
03
First trimester: propylthiouracil (PTU) preferred at lowest effective dose to minimise teratogenicity (methimazole risk of aplasia cutis, choanal atresia)
04
Second and third trimester: switch to methimazole (lower risk of maternal hepatotoxicity than PTU)
05
Target free T4 in upper third of normal range using lowest possible dose; avoid block-and-replace strategy
06
Beta-blockers (propranolol 20-40 mg every 6-8 hours) for symptom control; avoid prolonged use (fetal growth restriction)
07
TRAb measurement in second and third trimester to assess fetal risk; high titres (over 3 times upper limit) require fetal surveillance
08
Thyroidectomy in second trimester for severe disease unresponsive to medical therapy or drug intolerance
09
Postpartum: monitor for relapse and postpartum thyroiditis; methimazole compatible with breastfeeding at low doses

Which Department to Visit?

You can visit our Kadın Hastalıkları ve Doğum department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.