Thyroid Disorders in Pregnancy

Symptoms

• Fatigue (Hypothyroidism)
• Excessive weight gain (Hypothyroidism)
• Constipation (Hypothyroidism)
• Cold intolerance (Hypothyroidism)
• Dry skin (Hypothyroidism)
• Muscle cramps (Hypothyroidism)
• Difficulty concentrating (Hypothyroidism)
• Goiter (enlarged thyroid gland) (Less common Hypothyroidism)
• Bradycardia (slow heart rate) (Less common Hypothyroidism)
• Hoarseness (Less common Hypothyroidism)
• Depression (Less common Hypothyroidism)
• Preeclampsia (Less common Hypothyroidism)
• Palpitations (Hyperthyroidism)
• Tachycardia (fast heart rate) (Hyperthyroidism)
• Heat intolerance (Hyperthyroidism)
• Anxiety (Hyperthyroidism)
• Tremor (Hyperthyroidism)
• Poor weight gain or weight loss despite normal or increased appetite (Hyperthyroidism)
• Hyperemesis (severe morning sickness) (Hyperthyroidism)
• Goiter (enlarged thyroid gland) (Less common Hyperthyroidism)
• Ophthalmopathy (bulging eyes, specific to Graves' disease) (Less common Hyperthyroidism)
• Insomnia (Less common Hyperthyroidism)
• Frequent bowel movements (Less common Hyperthyroidism)
• Thyroid Storm (Thyrotoxic Crisis): A rare, life-threatening severe form of hyperthyroidism with high fever, very fast heart rate, irregular heartbeats, confusion, agitation, and heart failure. This is a medical emergency.
• Myxedema Coma: A rare, life-threatening complication of severe hypothyroidism, extremely uncommon during pregnancy.

Causes & Risk Factors

• Autoimmune (Hashimoto's thyroiditis) for Hypothyroidism: The most common cause in areas with enough iodine.
• Iodine Deficiency for Hypothyroidism: The most common cause worldwide.
• Iatrogenic for Hypothyroidism: Previous medical treatments such as thyroidectomy (thyroid removal surgery) or radioactive iodine therapy.
• Inadequate Levothyroxine Dosing for Hypothyroidism: For women already taking medication for hypothyroidism, the dose may need to be increased during pregnancy due to higher demands.
• Autoimmune (Graves' disease) for Hyperthyroidism: Accounts for about 85% of hyperthyroidism cases in pregnancy, caused by antibodies that stimulate the thyroid.
• hCG-Mediated (Gestational Transient Thyrotoxicosis - GTT) for Hyperthyroidism: High levels of the pregnancy hormone human chorionic gonadotropin (hCG) can temporarily stimulate the thyroid, usually in the first trimester.
• Nodular Thyroid Disease for Hyperthyroidism: Less common causes include toxic multinodular goiter or toxic adenoma.
• Personal history of thyroid disease (e.g., Hashimoto's thyroiditis) or prior thyroid surgery/ablation (for Hypothyroidism)
• Presence of thyroid peroxidase (TPO) antibodies (for Hypothyroidism)
• Family history of autoimmune thyroid disease (for Hypothyroidism)
• Goiter (enlarged thyroid gland) (for Hypothyroidism)
• Symptoms suggestive of thyroid dysfunction (for Hypothyroidism)
• Type 1 diabetes mellitus or other autoimmune disorders (for Hypothyroidism)
• History of miscarriage or preterm delivery (for Hypothyroidism)
• History of head or neck radiation (for Hypothyroidism)
• Age over 30 years (for Hypothyroidism)
• Obesity (BMI of 40 kg/m² or higher) (for Hypothyroidism)
• Residence in an area of known moderate-to-severe iodine insufficiency (for Hypothyroidism)
• History of infertility (for Hypothyroidism)
• Personal or family history of Graves' disease (for Hyperthyroidism)
• Hyperemesis gravidarum (severe morning sickness) (for Gestational Transient Thyrotoxicosis)
• Multiple gestation (carrying multiple babies) (for Gestational Transient Thyrotoxicosis)
• Iodine intake (deficiency or excess) (Modifiable)
• Genetic predisposition (Non-modifiable)
• Personal or family history of autoimmune disease (Non-modifiable)
• Age (Non-modifiable)
• Prior medical treatments (radiation, surgery) (Non-modifiable)

Diagnosis

• Medical History and Physical Exam: Your doctor will ask about your personal and family history of thyroid or autoimmune diseases and any previous pregnancy outcomes. A physical exam will check your thyroid gland for size, texture, and any lumps, and look for signs of overactive or underactive thyroid, including eye changes specific to Graves' disease.
• Laboratory Tests: TSH (Thyroid-Stimulating Hormone) is the main screening test. Free T4 (FT4) is measured if your TSH levels are abnormal. Thyroid antibodies, including TPOAb (Thyroid Peroxidase Antibodies) for Hashimoto's thyroiditis and TRAb (TSH Receptor Antibodies) for Graves' disease, are also tested.
• Diagnostic Criteria: It is essential to use pregnancy-specific and trimester-specific reference ranges for TSH and FT4. Overt hypothyroidism is diagnosed when TSH is above the trimester-specific upper limit with FT4 below the lower limit. Subclinical hypothyroidism is when TSH is above the trimester-specific upper limit with normal FT4. Overt hyperthyroidism is diagnosed when TSH is below the trimester-specific lower limit (often <0.1 mU/L) with elevated FT4 and/or FT3. Subclinical hyperthyroidism is when TSH is below the trimester-specific lower limit with normal FT4 and FT3.
• Note on TSH Levels: The ideal upper limit for TSH in the first trimester can vary. Some guidelines suggest an upper limit of 4.0 mU/L if specific lab ranges are not available, while some experts recommend a lower cutoff of 2.5 mU/L.
• Thyroid Ultrasound: This is safe during pregnancy and helps evaluate the thyroid gland's size, structure, and any nodules.
• Radioactive Iodine Uptake and Scan (RAIU): This test is absolutely contraindicated during pregnancy and is never performed.

Treatment Options

• Levothyroxine (LT4) for Hypothyroidism: This is the preferred medication and is safe during pregnancy. If you have hypothyroidism before pregnancy, your dose will likely need to increase by 25-30% once pregnancy is confirmed. Your TSH levels will be checked every 4-6 weeks during the first half of pregnancy, and at least once between 26 and 32 weeks.
• Antithyroid Drugs (ATDs) for Hyperthyroidism (Graves' Disease): The lowest effective dose is used. Propylthiouracil (PTU) is generally preferred in the first trimester due to a lower risk of birth defects. Methimazole (MMI) is often preferred in the second and third trimesters due to a lower risk of liver problems for the mother compared to PTU.
• Beta-blockers for Hyperthyroidism: These can be used for a short time to help manage symptoms like a fast heart rate.
• Thyroidectomy (Surgical Treatment): Surgical removal of the thyroid may be considered for severe hyperthyroidism during the second trimester if you cannot tolerate antithyroid drugs, need very high doses, or are unable to take your medication consistently.
• Watchful Waiting: This approach may be suitable for mild subclinical hypothyroidism (especially if you don't have TPO antibodies and your TSH is below 10 mU/L), subclinical hyperthyroidism, or gestational transient thyrotoxicosis, which often resolves on its own.
• Referral: If you have overt thyroid dysfunction or require treatment during pregnancy, referral to an endocrinologist (a hormone specialist) is recommended.

Frequently Asked Questions