Pregnancy is one of the most amazing times in a woman’s life — and one of the most hormonally complex. While most people think about estrogen and progesterone, your thyroid gland also plays an essential role in a healthy pregnancy.

The thyroid affects your energy, metabolism, and—most importantly—your baby’s brain and nervous system development. If your thyroid isn’t functioning at its best, both you and your baby may face risks.

Let’s explore what every woman should know about thyroid health in pregnancy.

How Pregnancy Changes Thyroid Function

Your body works hard to support a growing baby, and that means your thyroid has to step up, too. Here are the main changes that occur:

Increased Demand

Pregnancy raises thyroid hormone needs by 30–50%. If your thyroid can’t meet this demand due to conditions like Hashimoto’s thyroiditis or thyroidectomy, this may result in hypothyroidism during pregnancy and the need for increased thyroid medication.

hCG Effect

Human chorionic gonadotropin (hCG) resembles TSH and stimulates the thyroid, particularly in the first trimester. High hCG levels are linked to increased thyroid hormone production and suppressed TSH. This relationship has been demonstrated in studies showing that as hCG rises, TSH falls and Free T3 increases.

Estrogen’s Role

Elevated estrogen levels during pregnancy increase thyroxine-binding globulin (TBG) production, which binds more thyroid hormone, reducing free hormone availability. To compensate, the thyroid produces more T3 and T4 — elevating total hormone levels while maintaining stable free hormone levels.
Tip: Always request Free T4 and Free T3 for accurate assessment—not just total hormone levels.

Iodine Requirements

Your iodine needs increase due to greater thyroid hormone production, increased excretion, and fetal thyroid development. Recommendations place daily iodine intake during pregnancy and breastfeeding at ~220–290 mcg, compared to ~150 mcg for non-pregnant women.

Common Thyroid Issues During Pregnancy

• Hypothyroidism: Most often caused by Hashimoto’s thyroiditis. If untreated, it increases the risk of miscarriage, anemia, preterm delivery, and impaired neurodevelopment in the baby.

• Hyperthyroidism: Usually due to Graves’ disease and increases risks for preeclampsia, premature birth, and low birth weight.

• Autoimmune Thyroid Disease: Both Hashimoto’s and Graves’ may improve when pregnant, but often revert to pre-pregnancy severity after delivery.

Postpartum Thyroiditis

Postpartum thyroiditis (PPT) is an autoimmune inflammation of the thyroid that typically appears within 12 months after delivery, miscarriage, or abortion.

• Prevalence: Affects approximately 5–10% of new mothers.

• Phases:

  1. Hyperthyroid phase (2–6 months postpartum) — anxiety, palpitations, heat intolerance.

  2. Hypothyroid phase (4–12 months postpartum) — fatigue, depression, weight gain.

  3. Recovery or permanent hypothyroidism — ~80% return to normal within 12–18 months; ~20% require lifelong thyroid replacement.

Because symptoms overlap with normal postpartum changes or depression, obtaining a thyroid panel is vital for accurate diagnosis.

Thyroid Testing in Pregnancy

Conventional care often includes only TSH and Free T4, which may miss important dysfunction. A recommended comprehensive prenatal thyroid panel includes:

• TSH

• Free T4

• Free T3

• TPO antibodies

• Thyroglobulin antibodies

Note: First-trimester TSH suppression is expected due to elevated hCG.

If thyroid dysfunction or medication use is present, labs should be checked every 4–6 weeks, or sooner if symptoms develop.

Treatment During Pregnancy

Hypothyroidism

• Levothyroxine (Synthroid) is the safest and most studied option.

• NDT (Natural Desiccated Thyroid) contains both T4 and T3, but because T4 crosses the placenta more effectively than T3, levothyroxine is preferred. Conversion issues may warrant carefully monitored NDT use.

• Many patients require a 20–30% increase in thyroid hormone during early pregnancy.

Hyperthyroidism

• PTU preferred in the first trimester due to lower risk of birth defects.

• Methimazole is used in the second and third trimesters.

• Beta-blockers may be used temporarily for symptom control (e.g., palpitations).

• Radioactive iodine is contraindicated.

• Thyroidectomy may be considered in the second trimester if medication fails or is not tolerated.

Nutrition & Lifestyle for Thyroid Health in Pregnancy

• Iodine: Essential for hormone production; sources include iodized salt, seafood, and dairy. Avoid excess.

• Selenium: Supports T4-to-T3 conversion and may lower autoimmune activity; found in Brazil nuts, sunflower seeds, fish, poultry, eggs.

• Iron & Ferritin: Low iron impairs thyroid function. Consume lean meats, beans, greens. Take supplements separately from thyroid medication.

• Vitamin D: Supports immunity; deficiency worsens autoimmunity. Ensure adequate sun exposure and diet.

Lifestyle factors:

• Sleep: 7–9 hours nightly.

• Stress management: Yoga, meditation, walking reduce cortisol, supporting thyroid hormone efficiency.

• Exercise: Light to moderate activity helps metabolism and mood; avoid overexertion if hyperthyroid.

• Medication timing: Take thyroid hormone on an empty stomach; avoid vitamins and minerals within 4 hours of dosing.

When to Talk to Your Doctor

• Before conception if you have thyroid disease.

• If you notice unusual fatigue, palpitations, weight changes, or swelling during pregnancy.

• If postpartum symptoms feel “beyond normal,” especially mood-related issues.

Conclusion

Your thyroid may be small, but during pregnancy it has a big job — supporting both you and your baby. With thoughtful testing, appropriate treatment, and focused nutrition and lifestyle care, you can optimize both your health and your baby’s development.

💡 Want to learn more about the thyroid?
Explore my Advanced Thyroid Management Course  for deeper insights into thyroid testing, treatment strategies, and patient care.