OB

Thyroid Dysfunction in Pregnancy

search

Thyroid Dysfunction in Pregnancy, Thyroid Disease in Pregnancy

  • Physiology
  • Pregnancy specific Thyroid changes
  1. Thyroid hormone requirements increase by 20-40% in pregnancy (as early as 4 weeks gestation)
    1. Thyroid Binding Globulin increases (Estrogen mediated)
    2. Thyroid hormone (Thyroxine) has a greater volume of distribution
    3. Placental metabolism of Thyroxine
  2. Thyroid function markers are less reliable in pregnancy
    1. Serum TSH normal range is lower in pregnancy (due to cross-reaction with aHCG)
    2. Serum T4 Free is affected by serum binding protein level changes
  • Indications
  • Thyroid testing in pregnancy
  1. Many Prenatal Lab testing protocols routinely include Thyroid Stimulating Hormone (TSH)
  2. Current or prior Thyroid disorder management
    1. Hypothyroidism
    2. Hyperthyroidism
    3. ThyroidGoiter
    4. Postpartum Thyroid dysfunction history
  3. Family History of autoimmune Thyroid disease (e.g. Grave's Disease, Hashimoto's Thyroiditis)
  4. Type I Diabetes Mellitus
  5. Autoimmune disorder history
  6. High dose neck radiation exposure history
  7. Neontal Hypothyroidism with prior delivery
  1. Serum Thyroid Stimulating Hormone (TSH) normal ranges
    1. Non-pregnanct: 0.3 to 4.3 mIU/ml
    2. First trimester: 0.1 to 2.5 mIU/ml
    3. Second trimester: 0.2 to 3.0 mIU/ml
    4. Third timester: 0.3 to 3.0 mIU/ml
  2. Free Thyroxine (Free T4) normal ranges
    1. Non-pregnant: 0.8 to 1.7 ng/dl
    2. First trimester: 0.8 to 1.2 ng/dl
    3. Second trimester: 0.6 to 1.0 ng/dl
    4. Third timester: 0.5 to 0.8 ng/dl
  3. References
    1. Abbassi (2010) Obstet Gynecol 114(6): 1326-31 [PubMed]