Hyperthyroidism in Pregnancy

Aka: Hyperthyroidism in Pregnancy, Thyrotoxicosis in Pregnancy, Gestational Hyperthyroidism

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II. Pathophysiology

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

III. Findings

  1. See Hyperthyroidism
  2. May trigger Hyperemesis Gravidarum

IV. Labs

  1. See Thyroid Dysfunction in Pregnancy for normal lab values
  2. Serum TSH
  3. Free T4 (Free Thyroxine)
    1. Goal Free T4 <1.8 ng/dl
  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. Thyroid Goiter
      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 (lowest effective dose that keeps Free T4 <1.8 ng/dl)
    1. First trimester (and if trying to conceive)
      1. Propylthiouracil (risk of liver failure, hence then change to Methimazole after first trimester)
    2. Second and third trimester (and in Lactation)
      1. Methimazole (risk of Congenital Anomaly in the first trimester)
  3. Symptomatic management
    1. Consider Beta Blocker (Propranolol or Metoprolol) for first 2-6 weeks while initiating antithyroid medication

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

  1. Maternal
    1. Heart Failure
    2. Placental Abruption
    3. Preeclampsia
    4. Preterm delivery
  2. Fetal
    1. Intrauterine Growth Retardation (and Small for Gestational Age birth)
    2. Thyroid dysfunction
    3. Neonatal Goiter

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
    2. Requires avoiding close contact with the infant 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

XI. References

  1. (2018) Presc Lett 25(11): 65
  2. Carney (2014) Am Fam Physician 89(4): 273-8 [PubMed]
  3. De Groot (2012) J Clin Endocrinol Metab 97(8): 2543-65 [PubMed]
  4. Stagnaro-Green (2011) Thyroid 21(10): 1081-125 [PubMed]

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