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Gestational Subclinical Hypothyroidism

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Thyroid Diseases in Pregnancy

Abstract

Subclinical hypothyroidism (SCH) is a biochemical diagnosis characterised by an elevated serum thyrotropin (TSH) concentration and a normal serum total or free thyroxine (FT4) level and occurs commonly in asymptomatic pregnant women with a frequency ranging from 2 to 20%. Its importance is that observational studies have linked SCH to a large variety of adverse outcomes in both mother and foetus, but intervention trials with Levo-thyroxine (LT4) replacement have shown no therapeutic benefit. Despite publication of several expert sets of management guidelines from relevant professional bodies over the past decade, consensus is lacking on specific laboratory diagnostic criteria, case-detection or universal screening and indications and outcomes from LT4 replacement therapy. In this review, we explore and compare the various serum TSH values and reference ranges recommended for diagnosis of gestational SCH; and the factors impacting these values and ranges, such as iodine deficiency and excess, underlying thyroid autoimmunity and the effect of the different analytical platforms used for measuring TSH levels. The application of American Endocrine Society guidelines results in possible overdiagnosis and overtreatment of SCH compared with the American Thyroid Association (ATA) guidelines where the reverse may apply in a small percentage of patients. We illustrate this finding with a comparative analysis of data on over 1000 women from our clinic screened for thyroid dysfunction during the first trimester of pregnancy. We conclude that systematic screening for hypothyroidism by TSH testing early in pregnancy may be worthwhile, being superior to recommended case-detection guidelines, and that low dose LT4 therapy should be introduced even when the degree of hypothyroidism is mild and does not cause immediate clinical manifestations in the woman. The evidence is that diagnosis and treatment should take place as soon as possible after pregnancy has been confirmed in the first trimester and should be monitored carefully throughout the pregnancy to prevent overtreatment.

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Author information

Authors and Affiliations

  1. Faculty of Medicine and Health Sydney Medical School, The University of Sydney NSW Australia and Consultant Emeritus Westmead Hospital, Westmead, NSW, Australia

    Creswell J. Eastman

  2. Consultant Obstetrician and Gynaecologist Blacktown Hospital and Notre Dame University, Sydney, NSW, Australia

    Norman J. Blumenthal

Authors
  1. Creswell J. Eastman
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  2. Norman J. Blumenthal
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Correspondence to Creswell J. Eastman .

Editor information

Editors and Affiliations

  1. Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Fereidoun Azizi

  2. Reproductive Endocrinology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Fahimeh Ramezani Tehrani

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Eastman, C.J., Blumenthal, N.J. (2022). Gestational Subclinical Hypothyroidism. In: Azizi, F., Ramezani Tehrani, F. (eds) Thyroid Diseases in Pregnancy. Springer, Cham. https://doi.org/10.1007/978-3-030-98777-0_7

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  • DOI: https://doi.org/10.1007/978-3-030-98777-0_7

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  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-030-98776-3

  • Online ISBN: 978-3-030-98777-0

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