TSH and fT4 during pregnancy: an observational study and a review of the literature

Annemiek M.C.P. Joosen; Ivon J.M. van der Linden; Neletta de Jong-Aarts; Marieke A.A. Hermus; Antonius A.M. Ermens; Monique J.M. de Groot

doi:10.1515/cclm-2015-0629

Article

TSH and fT4 during pregnancy: an observational study and a review of the literature

Annemiek M.C.P. Joosen , Ivon J.M. van der Linden , Neletta de Jong-Aarts , Marieke A.A. Hermus , Antonius A.M. Ermens and Monique J.M. de Groot

Published/Copyright: December 7, 2015

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From the journal Clinical Chemistry and Laboratory Medicine (CCLM) Volume 54 Issue 7

Abstract

Background: Trimester-specific reference intervals for TSH are recommended to assess thyroid function during pregnancy due to changes in thyroid physiology. Laboratories should verify reference intervals for their population and assay used. No consistent upper reference limit (URL) for TSH during pregnancy is reported in literature. We investigated the use of non-pregnant reference intervals for TSH, recommended during pregnancy by current Dutch guidelines, by deriving trimester-specific reference intervals in disease-free Dutch pregnant women as these are not available.

Methods: Apparently healthy low risk pregnant women were recruited via midwifery practices. Exclusion criteria included current or past history of thyroid or other endocrine disease, multiple pregnancy, use of medication known to influence thyroid function and current pregnancy as a result of hormonal stimulation. Women who were TPO-antibody positive, miscarried, developed hyperemesis gravidarum, hypertension, pre-eclampsia, HELLP, diabetes or other disease, delivered prematurely or had a small for gestational age neonate were excluded. Blood samples were collected at 9–13 weeks (n=99), 27–29 weeks (n=96) and 36–39 weeks (n=96) of gestation and at 4–13 weeks post-partum (n=95). Sixty women had complete data during pregnancy and post-partum. All analyses were performed on a Roche Cobas e601 analyser.

Results and conclusions: In contrast to current Dutch guidelines, the 97.5th percentiles of TSH in the first (3.39 mIU/L) and second trimesters (3.38 mIU/L) are well under the non-pregnant URL of 4.0 mIU/L. The higher TSH in the third trimester (97.5th percentile 3.85 mIU/L) is close to the current non-pregnant URL of 4.0 mIU/L. Absolute intra-individual TSH is relatively stable during pregnancy and post-partum as individuals tracked within the tertile assigned in trimester 1. Even small deviations within the population reference interval may indicate subtle thyroid dysfunction.

Keywords: fT4; pregnancy; thyroid function; TSH

Corresponding author: Dr. Annemiek M.C.P. Joosen, Laboratory of Clinical Chemistry and Haematology, Amphia Hospital, Breda, The Netherlands, E-mail: a.joosen@elisabeth.nl

aPresent address: Laboratory of Clinical Chemistry and Haematology, St. Elisabeth Hospital, Hilvarenbeekseweg 60, 5022 GC Tilburg, The Netherlands

Acknowledgments

We gratefully acknowledge primary midwife practices Verloskundigen Etten-Leur, Trivia, De Moriaen, Doortje Uil, Verloskundig Centrum Breda, Het Zomerhuis, Prinsenbeemden, Het Klavertje, Luna, Vita and De Ooievaar and Origine birth center for recruitment of the volunteers. We thank Roche for providing the test kits.

Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

Research funding: None declared.

Employment or leadership: None declared.

Honorarium: None declared.

Competing interests: The funding organization(s) played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.

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Received: 2015-7-3

Accepted: 2015-10-23

Published Online: 2015-12-7

Published in Print: 2016-7-1

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Articles in the same Issue

https://doi.org/10.1515/cclm-2015-0629

Keywords for this article

fT4; pregnancy; thyroid function; TSH