What are the ACOG (American College of Obstetricians and Gynecologists) guidelines for screening, diagnosing, and managing thyroid disorders in pregnant women?

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Last updated: October 9, 2026 • View editorial policy

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ACOG Guidelines for Thyroid Management in Pregnancy

Screening Recommendations

ACOG does not recommend universal thyroid screening in all pregnant women; instead, screening should be targeted to symptomatic women or those with a history of thyroid disease 1. This selective approach is based on insufficient evidence to support universal screening, despite potential associations between maternal hypothyroidism and neurodevelopmental outcomes in children.

Who Should Be Screened:

  • Women with symptoms of thyroid dysfunction
  • History of thyroid disease
  • Presence of thyroid nodules or goiter
  • Clinical signs of hyperthyroidism or hypothyroidism

Note: While the 2002 ACOG guidelines took this conservative stance 1, more recent 2020 and 2026 updates 2, 3 may have evolved these recommendations, though the fundamental principle of targeted rather than universal screening remains relevant in clinical practice.

Diagnostic Testing

TSH is the recommended initial screening test for evaluating suspected thyroid disease in pregnancy 1. For pregnant women with suspected dysfunction:

  • Order TSH plus free T4 (FT4) or Free Thyroxine Index (FTI) for comprehensive evaluation
  • Use trimester-specific reference ranges (critical caveat: normal ranges differ from non-pregnant values)
  • Antibody testing may be useful in specific clinical situations

Management of Hypothyroidism

Treat hypothyroidism with levothyroxine in sufficient dosage to normalize TSH levels 1. The management algorithm is straightforward:

Treatment Protocol:

  • Goal: Return TSH to normal range using levothyroxine
  • Monitoring frequency: Adjust dosage every 4 weeks until TSH stabilizes
  • Maintenance monitoring: Check TSH every trimester once stable 1
  • Pre-gestational hypothyroidism: Requires higher levothyroxine doses (average 93.2 mcg/day) compared to gestational hypothyroidism (67.6 mcg/day) 4

Critical Pitfall:

Women with pre-existing hypothyroidism need early dose adjustments as pregnancy increases levothyroxine requirements significantly.

Management of Hyperthyroidism

Treat hyperthyroidism in pregnancy with thioamides (propylthiouracil or methimazole), with both agents showing equivalent safety profiles 1.

Treatment Algorithm:

  • Primary therapy: Propylthiouracil or methimazole (no significant differences in fetal outcomes or cord blood thyroid levels)
  • Treatment goal: Maintain FT4 or FTI in the high-normal range using the lowest effective thioamide dose
  • Monitoring: Measure FT4 or FTI every 2-4 weeks 1
  • Symptomatic management: Use beta-blockers (e.g., propranolol) for symptom control until thyroid hormone levels decrease

Safety Considerations:

  • Both thioamides are compatible with breastfeeding 1
  • Watch for agranulocytosis: If sore throat and fever develop, obtain CBC immediately and discontinue thioamide
  • Other side effects include hepatitis, vasculitis, and thrombocytopenia
  • Fetal thyroid suppression is usually transient and rarely requires treatment

Graves' Disease Monitoring:

  • Monitor maternal heart rate and fetal growth
  • Ultrasound screening for fetal goiter is NOT necessary unless problems detected 1
  • Inform neonatal team about maternal Graves' disease due to risk of neonatal thyroid dysfunction

Contraindications and Surgical Management:

  • Radioactive iodine (I-131) is absolutely contraindicated in pregnancy 1
  • Thyroidectomy reserved for women unresponsive to thioamides, preferably performed in second trimester 1
  • Women must not breastfeed for 4 months after I-131 treatment

Special Clinical Scenarios

Hyperemesis Gravidarum

Routine thyroid testing is NOT recommended for hyperemesis gravidarum unless other signs of hyperthyroidism are present 1. Biochemical hyperthyroidism (undetectable TSH, elevated FTI) commonly accompanies hyperemesis but rarely causes clinical hyperthyroidism requiring treatment.

Thyroid Storm

This is a life-threatening emergency with high risk of maternal heart failure that requires immediate treatment without waiting for confirmatory lab results 1.

Diagnostic Criteria (Clinical Diagnosis):

  • Fever
  • Tachycardia disproportionate to fever
  • Altered mental status (nervousness, restlessness, confusion, seizures)
  • Vomiting, diarrhea
  • Cardiac arrhythmia
  • Often preceded by inciting event (surgery, infection, labor, delivery)

Treatment Protocol:

  • Antithyroid agents: Propylthiouracil or methimazole
  • Iodine therapy: Saturated solution of potassium iodide, sodium iodide, Lugol's solution, or lithium
  • Corticosteroids: Dexamethasone
  • Supportive care: Oxygen, antipyretics, appropriate monitoring
  • Fetal monitoring: Ultrasound, NST, or biophysical profile based on gestational age
  • Avoid delivery during thyroid storm unless absolutely necessary 1

Thyroid Nodules and Cancer

All thyroid nodules must be evaluated, as up to 40% are malignant 1.

Management Options:

  • Thyroidectomy is the definitive treatment
  • Timing: Preferably second trimester if surgery needed during pregnancy
  • Radiation therapy (I-131) must be deferred until after pregnancy 1
  • Management decisions depend on gestational age and tumor characteristics

Postpartum Thyroiditis

Diagnose by new onset of abnormal TSH and/or FT4 levels postpartum 1.

Evaluation Indications:

  • Women who develop goiter during pregnancy or postpartum
  • Postpartum symptoms of hyper- or hypothyroidism (though some overlap with normal postpartum symptoms)
  • Treatment depends on severity of abnormality and symptoms
  • Highest risk for permanent hypothyroidism: Women with elevated TSH and high antithyroid peroxidase antibodies

Key Clinical Pitfalls to Avoid

  1. Using non-pregnant reference ranges for thyroid function tests—pregnancy requires trimester-specific values
  2. Universal screening—not recommended by ACOG; focus on high-risk populations
  3. Delaying treatment for thyroid storm—treat immediately based on clinical diagnosis
  4. Ultrasound screening for fetal goiter in all Graves' patients—only indicated if problems detected
  5. Inadequate levothyroxine dose adjustment—pre-gestational hypothyroidism requires significantly higher doses
  6. Missing agranulocytosis—any sore throat/fever on thioamides requires immediate CBC and drug discontinuation

References

1
Guideline

acog practice bulletin on thyroid disease in pregnancy.

American family physician, 2002

3
Research

American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum.

Thyroid : official journal of the American Thyroid Association, 2026

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