Hypothyroidism and Pregnancy Overview

Hypothyroidism and Pregnancy

• Maternal hypothyroidism during the first trimester can cause permanent neuropsychological issues in the child.
• Fetal thyroid function fully develops by the second trimester, enabling the fetus to produce its own hormones.
• Early diagnosis and treatment of hypothyroidism are crucial.
• Pregnant women taking thyroid supplements require a dosage increase, often by 50%, starting between four and eight weeks.

Thyroid Hormone Preparations for Hypothyroidism (Levothyroxine)

• Levothyroxine (T4), a synthetic thyroxine, is the preferred drug for most hypothyroidism cases.
• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast, as food reduces absorption.
• Most levothyroxine is converted to T3 in the body.
• It has a prolonged half-life (approximately one month for plasma levels to reach plateau) and is highly protein-bound.
• Safe for all types of hypothyroidism.
• Adverse effects are rare. Acute overdose can lead to thyrotoxicosis (symptoms include tachycardia, angina, tremor, nervousness, insomnia, hyperthermia, heat intolerance, and sweating).
• Drugs that reduce levothyroxine absorption include H2 blockers, proton pump inhibitors, sucralfate, cholestyramine, colestipol, aluminum-containing antacids, calcium supplements, iron supplements, magnesium salts, and orlistat. Spacing administration by 4 hours is crucial.
• Drugs that accelerate levothyroxine metabolism include phenytoin, carbamazepine, rifampin, sertraline, and phenobarbital. Patients taking these drugs might need increased levothyroxine doses.
• Warfarin doses may need adjustment as levothyroxine speeds up vitamin K-dependent clotting factor breakdown.
• Catecholamines' effect may increase due to thyroid hormones' impact on cardiac responsiveness.
• Levothyroxine can increase insulin and digoxin needs. Dosages of these drugs might need adjustment when treating a hypothyroid patient to an euthyroid state.
• Levothyroxine has a narrow therapeutic index. Precise control of plasma levels is essential.
• Bioequivalent products are critical when switching brands, and the prescriber should be notified of any changes.
• Almost always administered orally, once daily on an empty stomach. IV administration might be used in myxedema coma.
• Evaluation: A combination of clinical judgment and lab tests (serum TSH) is used to determine dosage. Elevated TSH levels declining indicate successful treatment. TSH normalization is gradual, and evaluation should occur 6-8 weeks after initiating treatment.
• Occasionally Serum T4 is used for evaluation as TSH may remain elevated despite restored thyroid hormone levels..
• Replacement therapy is typically lifelong; resolution of symptoms does not mean cessation.

Drugs for Hyperthyroidism (Methimazole)

• Methimazole (first-line) inhibits thyroid hormone synthesis.
• Not used during first trimester of pregnancy, but can be used in the second/third trimester.
• Therapy may take 3 to 12 weeks for treatment to be fully effective.
• Well absorbed orally, crosses membranes (including placenta and breast milk).
• Relatively long half-life (6-13 hours), allowing once-daily dosing. Effective in Graves' disease, radiation therapy support, surgical prep, and thyrotoxic crisis.
• Adverse effects include:
  • Agranulocytosis (most dangerous toxicity; sore throat, fever; early indications; immediate reporting).
  • Hypothyroidism (high dosage).
• Effects in pregnancy:
  • Neonatal hypothyroidism, goiter, and congenital hypothyroidism are possible, particularly in first trimester.
• PTU is preferred over methimazole in first-trimester pregnancy due to its lower placental crossing potential.
• Effects on breastfeeding are minimal, up to 20 mg daily isn't problematic.

Radioactive Iodine

• Specialist-prescribed for destroying thyroid tissue (Graves' disease).
• Relatively low cost, avoids surgery.
• Effective treatment, but delayed (several months for max effect).
• Risks include delayed hypothyroidism.
• Contraindicated in pregnancy and lactation.
• Dosage determined by thyroid size and iodine uptake.

Patient-Centered Care Across the Lifespan

• Infants: Hypothyroidism treatment; three-year regimen.
• Children/Adolescents: Thyroid hormone and Antithyroid drugs. Iodine not typical. Dosing individualized.
• Pregnant women: Iodine-131 contraindicated; first-trimester Methimazole avoidance.
• Breastfeeding women: Thyroid hormone and antithyroid medications generally safe.
• Older adults: Thyroid dysfunction is prevalent, requiring timely treatment with hormone and antithyroid medications for better health outcomes.