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Hyperthyroidism during pregnancy

Maternal pregnancy complications


Hyperthyroidism is characterized by excessive activity (hyperactivity) of the thyroid gland. Diagnosis is confirmed by blood tests.

Hyperthyroidism affects about 1% of women, especially between 25 and 50 years old.

If diagnosed during pregnancy, it may be transient or permanent. It often occurs in the first trimester. When it persists and is not well controlled, there is an increased risk of hypertension during gestational pregnancy, low birth weight, prematurity, and hemorrhage at delivery.


The causes of hyperthyroidism are diverse:

  • Autoimmune thyroid disease
  • Iodine excess (often due to medical reasons)
  • Tumour of the thyroid gland
  • Inflammation of the thyroid


Hyperthyroidism causes the following symptoms:

  • Weight loss
  • Increased heart rate
  • Intense sweating (diaphoresis)
  • Bulging eyes (exophthalmos)
  • Digestive disorders (diarrhea)
  • Heat intolerance
  • Insomnia

Tests and procedures

Close monitoring of free T4 is done through a series of blood tests.

When hyperthyroidism is caused by antibodies that stimulate the thyroid, these antibodies can cross the placenta and affect the fetus. Some medications, such as propylthiouracil (PTU) or methimazole may also affect the thyroid function of the fetus during the mother’s required treatment. In these situations, ultrasound monitoring of the thyroid of the fetus is necessary.

Treatment and follow-up care

The obstetrical team closely monitors the entire pregnancy.

Treatment to control the symptoms is proposed. For example, a beta-blocker like propranolol is often used to control maternal tachycardia. Generally, synthetic anti-thyroid drugs such as UTP or methimazole are also needed to enable the pregnant woman to regulate her basal metabolism and gain weight. Medications given to the mother, however, can lead to hypothyroidism in the newborn.

In cases where there is drug intolerance or treatment is aggravating or simply ineffective, surgery might be recommended.

Resources and useful links

Page by

Josée Normandeau, inf. clinicienne, Dre Kateri Lévesque et Dre Lucie Morin

About this page
Updated on 1/25/2021
Created on 12/19/2017
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