Overview

Pregnancy involves significant physiological changes, during which the body adapts to support the growing foetus. Among the many changes, the thyroid gland undergoes significant adaptations to meet the increased metabolic (energy level) demands of both the pregnant individual and the baby. While most pregnant people experience these changes without complications, those with pre-existing thyroid disorders, particularly hyperthyroidism, may face serious risks. One of the most critical and life-threatening complications of uncontrolled hyperthyroidism is thyroid storm, also known as thyrotoxic crisis.

Thyroid storm is a rare but potentially fatal complication of a condition called thyrotoxicosis, leading to multi-organ failure and high mortality rates if left untreated.¹ In pregnancy, the stakes are even higher, as both maternal and foetal well-being are at risk. The challenge lies in diagnosing thyroid storm promptly, as pregnancy itself can mimic some hyperthyroid symptoms, such as increased heart rate, heat intolerance and fatigue.² Additionally, managing thyroid storm during pregnancy requires a delicate balance, as many standard treatment options must be carefully chosen to avoid harming the developing fetus.

This article explores the complexities of thyroid storm during pregnancy, highlighting the obstacles in diagnosis and treatment while also discussing maternal-foetal outcomes and strategies for preventing severe complications.

Understanding thyroid storm

What is thyroid storm?

Thyroid storm is a severe and acute form of hyperthyroidism, where the body is overwhelmed by high levels of thyroid hormones— triiodothyronine (T3) and thyroxine (T4). Thyroid storm can either arise in response to the overproduction of hormones or an altered response to these hormones.³ These hormones are produced by the thyroid gland, a butterfly-shaped gland found in the neck, directly in front of the trachea (windpipe). This leads to dangerous overstimulation of the endocrine system and thus metabolism, affecting multiple organ systems. Without immediate treatment, it can result in severe complications such as heart failure, seizures and even death.

What causes a thyroid storm?

Thyroid storm is often triggered by factors which increase stress on the body, such as:

• Untreated or poorly managed hyperthyroidism (especially in Graves’ disease)
• Infections or illnesses (e.g., pneumonia, urinary tract infections, COVID-19, diabetic ketoacidosis, heart complications)
• Surgery or trauma (e.g., burns) 
• Labour and delivery
• Reaction to drugs (e.g., anaesthetics, amiodarone and salicylates)
• Stopping thyroid medication suddenly
• Stroke or traumatic brain injury
• Hyperemesis gravidarum in pregnancy
• Recent exposure to iodinated contrast medium
• Radioiodine therapy (rare during pregnancy)⁴

Hyperthyroidism in pregnancy

Thyroid hormones play an important role in foetal development. As the thyroid gland increases in size to meet the demands of pregnancy (including early-stage neurodevelopment and growth), the result is higher levels of circulating T3 and T4.^5,6 The hormone human chorionic gonadotropin (hCG), which is produced by the placenta during pregnancy, causes the thyroid to produce less thyroid stimulating hormone (TSH), leading to higher levels of circulating thyroid hormones.² Hyperthyroidism occurs in between 0.2% and 0.9% of pregnancies, and occurs most frequently during the first trimester and is often linked to autoimmune disorders such as Graves’ disease (where the body’s immune system attacks the thyroid, resulting in increased production of thyroid hormones).^2,7 Hyperthyroidism can lead to complications such as premature labour and birth, low birth weight, preeclampsia, intrauterine growth restriction (IUGR) and gestational hypertension.² 

What causes hyperthyroidism in pregnancy?

An estimated 2.97 per 1,000,000 pregnancies result in thyroid storm.⁷ In pregnancy, hyperthyroidism can be triggered by:

• Graves' disease
• hCG-mediated hyperthyroidism due to gestational transient thyrotoxicosis
• Multinodular toxic goiter
• Toxic thyroid adenoma
• Struma ovarii 
• Factitious thyroid hormone intake
• Subacute thyroiditis
• TSH-secreting pituitary adenoma
• Hydatidiform mole
• Metastatic functional thyroid cancer 

If left untreated, hyperthyroidism can lead to thyroid storm, requiring critical medical attention with a mortality or death rate of 3-11% of thyroid storm patients admitted to the hospital.⁷

Symptoms of thyroid storm

Thyroid storm symptoms develop quickly and are much more severe than regular hyperthyroidism. Signs include:

• Very high fever (above 38.5°C)
• Severe fast heartbeat (tachycardia), sometimes over 140 beats per minute
• Irregular heartbeat or palpitations
• Confusion, agitation, or even coma
• Severe nausea, vomiting, and diarrhoea
• Extreme sweating and dehydration
• Difficulty breathing or swelling due to congestive heart failure
• Cardiac arrhythmias⁷

How is thyroid storm diagnosed?

Medical professionals use the Burch-Wartofsky Point Scale (BWPS) to determine if a patient is experiencing a thyroid storm. This scoring system considers symptoms such as fever, heart rate and mental state. A score above 45 strongly indicates thyroid storm and requires urgent treatment. The severity of the thyroid storm can be assessed using the Japan Thyroid Association (JTA) criteria.⁸

Table 1: Comparing hyperthyroidism and thyroid storm

How is thyroid storm treated?

The management of thyroid storm should begin immediately in a stepwise order in the intensive care unit (ICU) under the care of a multidisciplinary team to save the lives of both the pregnant person and the baby.⁷ By ensuring a multidisciplinary approach involving endocrinologists, obstetricians, paediatricians and critical care specialists, the negative outcomes associated with thyroid storm can potentially be mitigated. The goal is not just to manage the crisis but to ensure optimal long-term health for both mother and child. The main goals are to:

• Stop thyroid hormone production
• Block the effects of excess thyroid hormones
• Provide supportive care for the functions of vital organs

Medications to reduce thyroid hormones

• Propylthiouracil (PTU) – Used in early pregnancy (first trimester), as it is safer for the baby
• Methimazole (MMI) – Used later in pregnancy (second and third trimester), but avoided in the first trimester due to birth defect risks
• Iodine solutions (Lugol’s iodine or potassium iodide) – Temporarily stop the thyroid from releasing more hormones
• Cholestyramine (a bile acid sequestrant) reduces T3 and T4 levels in the liver’s circulation

Beta-blockers to reduce adrenergic tone

The following helps to mitigate the effects of the body’s “fight” response due to high thyroid hormone levels:

• Esmolol is the preferred beta-blocker because it is fast-acting (short half-life)
• Propranolol is the 2nd line beta-blocker, but can worsen heart complications
• Atenolol should be avoided due to potential restrictions on foetal growth⁷

Steroids (corticosteroids) to treat the peripheral effects of thyroid hormones

• Hydrocortisone or dexamethasone helps stop the conversion of T4 into the more active T3 hormone
  • Hydrocortisone is preferred, as dexamethasone crosses the placenta
• Steroids may also be beneficial to reverse the effects of insufficient serum cortisol during thyroid storm⁷

Supportive care

• IV fluids to prevent dehydration from excessive sweating and diarrhoea
• Crystalloids for fluid loss
• Cooling measures such as paracetamol, cold compresses or cooling blankets to lower fever
• Oxygen therapy for pregnant people experiencing breathing difficulties
• Continuous foetal monitoring to detect any signs of distress in the baby

Plasmapheresis and charcoal plasma perfusion

Physical removal of thyroid hormones can be attempted through plasmapheresis or charcoal plasma perfusion (the use of activated charcoal to remove substances from plasma):

• Risks include foetal distress due to transient low blood levels or low blood pressure
• Effects only last 48-72 hours; therefore, it is usually used before thyroid surgery or if thioamides are contraindicated

Thyroid surgery

As a last resort, a thyroidectomy (surgical removal of all or part of the thyroid) can be performed if medical management is unsuccessful. 

Maternal and foetal outcomes

With prompt treatment, most women survive a thyroid storm, but there are still risks:

Maternal risks

• Heart failure due to excessive strain on the cardiovascular system
• Organ failure from severe dehydration and metabolic stress
• Increased risk of preeclampsia, a dangerous pregnancy condition that raises blood pressure⁹

Foetal risks

• Preterm birth– Increased risk due to maternal instability
• Low birth weight– Caused by poor placental function.
• Neonatal hyperthyroidism
• Stillbirth or miscarriage in severe, untreated cases⁹

Preventing thyroid storm in pregnancy

While thyroid storm is a serious condition, it can sometimes be prevented:

• Preconception counselling – women with hyperthyroidism should consult a doctor before pregnancy to stabilise their thyroid levels
• Regular prenatal monitoring – thyroid function can be monitored through regular blood tests and should be performed throughout pregnancy in high-risk women
• Medication adherence – stopping thyroid medication suddenly can trigger thyroid storm
• Avoiding infection and stress, since these can trigger thyroid storm, it is essential to stay physically and mentally healthy during pregnancy

Summary

Thyroid storm in pregnancy is a rare but life-threatening medical emergency requiring immediate intervention. Pregnancy adds extra complexity to its diagnosis and treatment, but a multidisciplinary approach involving endocrinologists, paediatricians, obstetricians and critical care specialists improves maternal and foetal outcomes. Awareness, early detection and comprehensive management remain key to preventing severe complications. Pregnant people with hyperthyroidism should receive appropriate preconception counselling to mitigate risks, and those with thyroid dysfunction must be closely monitored throughout gestation and postpartum to ensure both maternal and neonatal health.