Hyperthyroidism in Pregnancy: Causes, Risks, and Management

Hyperthyroidism in pregnancy occurs when the thyroid gland becomes overactive, producing excessive thyroid hormones (T3 and T4). These hormones regulate the body’s metabolism, and an imbalance can lead to complications for both mother and baby if left untreated. While uncommon, hyperthyroidism in pregnancy requires careful monitoring and management to ensure a safe and healthy pregnancy.

The most common causes of hyperthyroidism during pregnancy include:

1. Graves’ Disease

• Primary Cause: Graves’ disease, an autoimmune condition, accounts for 85% of hyperthyroidism cases in pregnancy. It occurs when the immune system produces antibodies (TSI) that overstimulate the thyroid gland.

• It can worsen during the first trimester due to hormonal changes and immune system modulation.

2. Gestational Transient Thyrotoxicosis (GTT)

• Hormonal Fluctuations: GTT occurs in early pregnancy due to elevated hCG (human chorionic gonadotropin), which stimulates the thyroid gland.

• GTT is temporary and usually resolves by the second trimester without treatment.

3. Thyroid Nodules or Toxic Adenomas

• Overgrowth of thyroid tissue can lead to excess hormone production.

4. Molar Pregnancy

• A rare condition where abnormal placental growth results in very high hCG levels, overstimulating the thyroid.

5. Pre-existing Hyperthyroidism

• Women with a history of hyperthyroidism before pregnancy may experience exacerbations during pregnancy.

Hyperthyroidism in pregnancy presents symptoms similar to those outside pregnancy, but some may overlap with normal pregnancy changes:

• Rapid heartbeat or palpitations.

• Excessive sweating.

• Unexplained weight loss or lack of expected weight gain.

• Nervousness, irritability, or anxiety.

• Heat intolerance.

• Tremors in the hands.

• Frequent bowel movements or diarrhea.

• Fatigue and muscle weakness.

• Enlarged thyroid gland (goiter).

If these symptoms are severe or persist, a medical evaluation is necessary.

Untreated or poorly managed hyperthyroidism can lead to complications for both the mother and baby:

Maternal Risks:

1. Pre-eclampsia: A condition marked by high blood pressure, which can be life-threatening.

2. Heart Problems: Increased risk of arrhythmias and heart failure due to the strain on the cardiovascular system.

3. Thyroid Storm: A rare but severe condition characterized by dangerously high thyroid hormone levels, leading to fever, rapid heartbeat, and delirium.

Fetal and Neonatal Risks:

1. Preterm Birth: Early delivery can increase the risk of complications in newborns.

2. Low Birth Weight: Babies may fail to grow adequately in utero.

3. Miscarriage or Stillbirth: Increased risk of pregnancy loss.

4. Neonatal Hyperthyroidism: Babies may develop hyperthyroidism if maternal thyroid-stimulating antibodies cross the placenta.

Hyperthyroidism is diagnosed through a combination of:

1. Clinical Evaluation:

• Symptoms and physical examination, including thyroid size and heart rate.

2. Blood Tests:

• TSH (Thyroid-Stimulating Hormone): Low levels indicate hyperthyroidism.

• Free T4 and T3: Elevated levels confirm excessive thyroid activity.

• Thyroid Antibodies: Tests for TSI can diagnose Graves’ disease.

3. Ultrasound or Imaging:

• Thyroid ultrasound may be used to assess nodules or goiter.

• Radioactive iodine tests are avoided during pregnancy due to fetal risks.

The treatment goal is to maintain thyroid hormone levels in the normal range while minimizing risks to the mother and baby.

1. Medications

• Antithyroid Drugs (ATDs)

• Propylthiouracil (PTU): Preferred in the first trimester due to lower risk of birth defects.

• Methimazole (MMI): Used in the second and third trimesters as it is more effective long-term.

• Regular monitoring of thyroid levels is essential to adjust doses and avoid overtreatment.

2. Beta-Blockers

• Prescribed short-term to manage symptoms like rapid heartbeat or tremors.

3. Surgery

• Thyroidectomy (surgical removal of the thyroid) may be considered in rare cases where medication is ineffective or contraindicated.

4. Monitoring and Follow-Up

• Frequent prenatal visits to monitor thyroid function, fetal growth, and development.

• Maternal and fetal ultrasound to check for complications.

After delivery, hyperthyroidism may improve or worsen:

• Postpartum Thyroiditis: Temporary thyroid dysfunction may occur in women with Graves’ disease.

• Breastfeeding is safe with most antithyroid medications, but doses should be closely monitored.

• Babies of mothers with hyperthyroidism should be checked for neonatal hyperthyroidism.

1. Preconception Planning:

• Women with pre-existing hyperthyroidism should stabilize thyroid levels before conceiving.

2. Nutritional Support:

• Avoid iodine-rich supplements unless prescribed.

• Eat a balanced diet to support overall thyroid health.

3. Regular Monitoring:

• Stay consistent with thyroid function testing throughout pregnancy.

4. Early Intervention:

• Report any concerning symptoms to your healthcare provider promptly.

Hyperthyroidism in pregnancy requires careful management to ensure the health and safety of both mother and baby. With early diagnosis, appropriate treatment, and regular monitoring, most women with hyperthyroidism can have successful pregnancies.