II. 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
    4. HCG is a weak TSH receptor stimulator in early pregnancy (decreases TSH levels), but normalizes by second trimester
  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

III. 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. Thyroid Goiter
    4. Postpartum Thyroid dysfunction history
    5. TPO Antibody Positive
  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

IV. Labs: Thyroid Testing

  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]

Images: Related links to external sites (from Bing)

Related Studies

Ontology: Thyroid disease in pregnancy (C0558372)

Concepts Disease or Syndrome (T047)
SnomedCT 156139008, 274120003
English thyroid disease in pregnancy, thyroid disease pregnancy, diseases pregnancy thyroid, Thyroid disease in pregnancy, Thyroid disease in pregnancy (disorder)
Spanish enfermedad tiroidea en el embarazo (trastorno), enfermedad tiroidea en el embarazo

Ontology: Thyroid dysfunction in pregnancy (C0747834)

Concepts Disease or Syndrome (T047)
ICD9 648.13
English Thyroid dysfunction, antepartum, Thyroid dysfunc-antepart, Thyroid dysfunction of mother, antepartum condition or complication, Thyroid dysfunction in pregnancy
Italian Disfunzione della tiroide in gravidanza, Disfunzione della tiroide, antepartum
Dutch schildklierdisfunctie, antepartum, schildklierdysfunctie tijdens de zwangerschap
French Dysfonctionnement thyroïdien, antepartum, Dysfonctionnement de la thyroïde pendant la grossesse
German Funktionsstoerung der Schilddruese, antepartal, Schilddruesenfunktionsstoerung waehrend der Schwangerschaft
Portuguese Disfunção tiroideia anteparto, Disfunção da tiroideia durante a gravidez
Spanish Disfunción tiroidea anteparto, Disfunción tiroidea en el embarazo
Japanese 甲状腺機能障害、分娩前, 妊娠時甲状腺障害, ニンシンジコウジョウセンショウガイ, コウジョウセンキノウショウガイブンベンゼン, コウジョウセンキノウショウガイブンベンマエ
Czech Dysfunkce štítné žlázy před porodem, Dysfunkce štítné žlázy v těhotenství
Hungarian Pajzsmirigy működési zavara, antepartum, Pajzsmirigy működési zavar a terhesség alatt