II. Pathophysiology

  1. Typically starts in first trimester
  2. B-HCG cross-stimulates TSH receptors

III. Findings

IV. Labs

  1. See Thyroid Dysfunction in Pregnancy for normal lab values
  2. Serum TSH
  3. Free T4 (Free Thyroxine)
  4. Thyroid Receptor Antibody Indications (by end of second trimester)
    1. Active Grave's Disease
    2. Grave's Disease history previously treated with Radioactive Iodine or Thyroidectomy
    3. History of prior infant with Neonatal Hyperthyroidism

V. Diagnostics: Fetal Assessment

  1. Indications: High risk for Hyperthyroidism complication
    1. Antithyroid medication use
    2. Poorly controlled Hyperthyroidism
    3. High Thyrotropin Receptor Antibody
  2. Fetal Ultrasound
    1. Perform monthly Fetal Ultrasound after 20 weeks
    2. Evaluate for fetal Thyroid dysfunction
      1. Hydrops fetalis
      2. Intrauterine Growth Retardation
      3. ThyroidGoiter
      4. Cardiac failure
  3. Antepartum testing
    1. Start testing at 32-34 weeks gestation (earlier if indicated by risk)
    2. Non-Stress Test
    3. Biophysical Profile

VI. Imaging: Contraindicated Studies

  1. Radioactive Iodine Uptake Scan
    1. Absolutely contraindicated in pregnancy

VII. Management

  1. Subclinical Hyperthyroidism is not typically treated in pregnancy
  2. Antithyroid medications
    1. First trimester
      1. Propylthiouracil (risk of liver failure, hence then change to Methimazole after first trimester)
    2. Second and third trimester
      1. Methimazole (risk of Congenital Anomaly in the first trimester)

VIII. Course: Grave's Disease

  1. Fluctuating course during pregnancy
  2. Hyperthyroidism symptoms increase in first trimester
    1. Results from HCG cross reactive stimulatory effect on the Thyroid
  3. Hyperthyroidism symptoms improve in second trimester
  4. Hyperthyroidism symptoms worsen in third trimester

IX. Complications

X. Prevention: Preconception Counseling

  1. Discuss options for women with known Hyperthyroidism well before planned conception if possible
  2. Discuss definitive management options prior to pregnancy
  3. Radioactive Iodine should be completed at least 6 months prior to pregnancy
    1. If performed after pregnancy, Radioactive Iodine will contraindicate Lactation and requires avoiding close contact for a period of time
  4. Both Radioactive Iodine and Thyroid resection can predispose infants to neonatal Goiter and neonatal Hyperthyroidism
    1. Results from unopposed maternal TSH receptor antibodies effect on the fetal Thyroid

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Ontology: Thyrotoxicosis in pregnancy (C0342138)

Concepts Disease or Syndrome (T047)
SnomedCT 237506002
English thyrotoxicosis in pregnancy, thyrotoxicosis pregnancy, Gestational thyrotoxicosis, Thyrotoxicosis in pregnancy, Thyrotoxicosis in pregnancy (disorder)
Spanish hipertiroidismo en el embarazo (trastorno), hipertiroidismo en el embarazo, hipertiroidismo gestacional, tirotoxicosis en el embarazo (trastorno), tirotoxicosis en el embarazo, tirotoxicosis gestacional

Ontology: pregnancy complicated by hyperthyroidism (C2113870)

Concepts Pathologic Function (T046)
English pregnancy complicated by hyperthyroidism (diagnosis), pregnancy complicated by hyperthyroidism