Hyperthyroidism and Pregnancy

Hyperthyroidism is a metabolic disorder that is characterized with the over-production of thyroid hormone. It is caused by an overactive thyroid gland during pregnancy. However, majority of pregnant women often mistake the signs and symptoms of hyperthyroidism to pregnancy symptoms. This is because hyperthyroidism presents with heat intolerance, nervousness, nausea,rapidly pounding heartbeat, insomnia, and weight loss, which are also signs that are experienced during pregnancy. However, it is impertinent that pregnant women with thyrotoxicosis get immediately treated to avoid the risk of birth defects and miscarriages. Read on to learn more about hyperthyroidism and pregnancy.

Altered physiology of thyroid gland during pregnancy

Clinically, the thyroid gland presents with the following changes that subside during postnatal period.

  • bilateral enlargement                                
  • Increased vascularity

Epidemiology of hyperthyroidism during pregnancy

  • In general, hyperthyroidism is most commonly caused by Graves’ disease, which is associated with overactive thyroid due to the production of thyrotrophin receptor stimulating antibodies (TRAb).
  • About 0.15% of pregnancies present with new-onset Graves’ hyperthyroidism.
  • The prevalence rate of Transient gestational hyperthyroidism accounts to about 2-3% of pregnancies.

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Causes of hyperthyroidism during pregnancy

Below are the most common causes that contribute to hyperthyroidism in pregnant women:

  • Graves’ disease
  • Toxic multinodular goitre
  • Struma ovarii
  • Transient gestational hyperthyroidism
  • Subacute thyroiditis
  • Single toxic adenoma
  • Activation of thyrotrophin receptor
  • Iodine-induced hyperthyroidism

Some of the causes that regress hyperthyroidism (or worsen thyroid control), despite controlling it during pregnancy include:

  • Stimulation of thyroid gland by an increased hCG hormone levels
  • High levels of Thyrotropin receptor stimulating antibodies during first trimester.
  • Vomiting that impairs the absorption of medication.
  • Infection
  • Labour
  • Caesarean section may also.

Types of maternal hyperthyroidism

Transient gestational thyrotoxicosis

  • It is characterized with the condition, thyroid storm (hyperemesis gravidarum).
  • It is mainly caused by increased levels of beta-hCG, which activates TSH receptor, thus the condition subsides after the hCG level reduces.
  • Commonly occurs in molar pregnancy.

Clinically, the patient presents with mild symptoms and is not thyrotoxic, hence treatment requires no specific anti-thyroid drug therapy.

Symptoms include:

  • Palpitations
  • Tachycardia
  • Systolic murmur
  • Heat intolerance
  • Weight loss despite having high appetite
  • Disturbed Bowel movements
  • Emotional upset


Graves’ disease

Patient with Graves’ hyper-thyroiditis present with diffuse goiter, ophthalmopathy, and pretibial myxoedema.

It worsens during first trimester, subsides during late pregnancy and regresses in postpartum

Common symptoms include:

  • Tremors
  • Weight loss
  • Insomnia
  • Mood swings
  • Rapid heart rate

Patients require low dose anti-thyroid medications.

Diagnostic tests

Thyroid function tests (TFTs) are done. Hyperthyroidism during pregnancy can be confirmed with free T4 levels. Primary thyrotoxicosis can be ruled out with serum TSH reports. Obtaining Free T3 level reports can be done as 5% of pregnant women present with T3 toxicosis. Pregnant women who have been treated previously for Graves’ disease require TSH, T3 and T4 tests.Thyrotrpin receptor stimulating antibody (TRAb) level should be determined during pregnancy as it has the capacity to cross placental barrier and can interfere with fetal thyroid function. In addition to that, Thyroid ultrasound scan can be performed. Serial ultrasonography test helps to diagnose fetal hyperthyroidism.

Complications of hyperthyroidism during pregnancy


Currently, subclinical hyperthyroidism is not associated with serious complications during pregnancy. The following complications occur if hyperthyroidism is poorly controlled or left untreated during pregnancy:

Maternal complications include: Preeclampsia, pregnancy-induced hypertension,highest rate of miscarriages, premature labor, cardiac failure, placental abruption, and thyroid storm, to include a few.

Neonatal or fetal complications include Low birth weight baby, dysfunctional thyroid gland, still birth,goiter formation,Intra-uterine growth retardation, tachycardia and heart failure,neonatal hyperthyroidism

Treatment for all types of hyperthyroidism during pregnancy


Hyperthyroidism during pregnancy can be effectively treated with anti-thyroid medications that reduce the production of thyroid hormones. These drugs work by inhibiting the over-active function of thyroid gland. These drugs provide best results by controlling the symptoms of hyperthyroidism within few weeks of therapy. Propylthiouracil (PTU) has been considered as the safest drug for pregnant women.

  • Pregnant women with hyperthyroidism are advised to seek pre-pregnancy follow-up and specialist care for close monitoring purpose of thyroid tests and medications.
  • Anti-thyroid drugs are considered to be the preferred treatment of choice to treat all pregnancy cases with hyperthyroidism.
  • Various hyperthyroidism complications during pregnancy can be be prevented with anti-thyroid medications such as Methimazole and propylthiouracil (PTU)
  • Radioiodine is an absolute contra-indication in pregnant women.
  • Surgery is a last option and should be done only on euthyroid patients during the second trimester of pregnancy.
  • Adrenergic symptoms may require short term therapy with beta-blocker drugs

Recommended anti-thyroid drugs include:

  • Propylthiouracil medication during the first trimester and carbimazole during the second and third trimesters of pregnancy.
  • The dose of propylthiouracil can be gradually reduced on stabilizing the thyroid hormone levels as it can cause neonatal hypothyroidism.
  • Recommended medications should be continued until labor at a lower dosing.