Thyroid Physiology During Pregnancy

Rodrigo Arrangoiz MS, MD, FACS, FSSO
  • Significant changes in thyroid physiology occur during pregnancy:
    • This can make the interpretation of serum thyroid function tests challenging
  • During the first trimester of pregnancy:
    • Serum thyroxine binding globulin (TBG) concentrations increase by up to 50%:
      • As a result of altered estrogen induced glycosylation:
        • Which prolongs TBG half-life
    • The elevated TBG levels increase the quantities of protein-bound T4 and T3:
      • Which results in an increase in total serum T4 and T3 concentrations:
        • However, in euthyroid individuals:
          • The active or free levels of T4 and T3 remain normal
  • In addition, during the first trimester of pregnancy:
    • Levels of placental human chorionic gonadotropin (hCG) steadily increase:
      • Because hCG is a weak TSH receptor agonist:
        • This results in a small increase of free T4 (although still within the normal range) and a concomitant decrease in TSH:
          • Below the lower reference range in up to 15% of normal women in the first trimester
  • Serum TSH concentrations:
    • Should thus be assessed using trimester-specific ranges during pregnancy
  • The changes of reduced TSH and elevated FT4 are more pronounced:
    • In pregnancies associated with higher levels of hCG:
      • Such as multiple gestations and hyperemesis gravidarum, and are most extreme in hydatidiform moles
    • The physiologic suppression of TSH does not require medical intervention and usually normalizes after the first trimester of pregnancy
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Published by Rodrigo Arrangoiz MS, MD, FACS, FSSO

My name is Rodrigo Arrangoiz I am a breast surgeon/ thyroid surgeon / parathyroid surgeon / head and neck surgeon / surgical oncologist that works at Center for Advanced Surgical Oncology in Miami, Florida. I was trained as a surgeon at Michigan State University from (2005 to 2010) where I was a chief resident in 2010. My surgical oncology and head and neck training was performed at the Fox Chase Cancer Center in Philadelphia from 2010 to 2012. At the same time I underwent a masters in science (Clinical research for health professionals) at the University of Drexel. Through the International Federation of Head and Neck Societies / Memorial Sloan Kettering Cancer Center I performed a two year head and neck surgery and oncology / endocrine fellowship that ended in 2016. Mi nombre es Rodrigo Arrangoiz, soy cirujano oncólogo / cirujano de tumores de cabeza y cuello / cirujano endocrino que trabaja Center for Advanced Surgical Oncology en Miami, Florida. Fui entrenado como cirujano en Michigan State University (2005 a 2010 ) donde fui jefe de residentes en 2010. Mi formación en oncología quirúrgica y e n tumores de cabeza y cuello se realizó en el Fox Chase Cancer Center en Filadelfia de 2010 a 2012. Al mismo tiempo, me sometí a una maestría en ciencias (investigación clínica para profesionales de la salud) en la Universidad de Drexel. A través de la Federación Internacional de Sociedades de Cabeza y Cuello / Memorial Sloan Kettering Cancer Center realicé una sub especialidad en cirugía de cabeza y cuello / cirugia endocrina de dos años que terminó en 2016.

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