Available online 24 November 2022

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During pregnancy, thyroid function disorders are associated with multiple complications, both maternal and foetal. In recent years, numerous Clinical Practice Guidelines have been developed to facilitate the identification and correct management of thyroid disease in pregnant women. However, this proliferation of guidelines has led to confusion by proposing different cut-off points for reference values and different recommendations for similar situations. For this reason, the Sociedad Española de Endocrinología y Nutrición and the Sociedad Española de Ginecología y Obstetricia have prepared this Consensus Document, with the aim of creating a framework for joint action to unify criteria for the diagnosis and treatment of thyroid dysfunction in these patients. The document is structured to answer the most frequently asked questions in clinical practice, grouped into five sections: 1/Reference values for thyroid function tests and screening during pregnancy 2/Iodine nutrition 3/Hypothyroidism and pregnancy 4/Hyperthyroidism and pregnancy 5/ Thyroid autoimmunity.

Resumen

Durante la gestación, las alteraciones de la función tiroidea se asocian a múltiples complicaciones, tanto maternas como fetales. En los últimos años se han elaborado numerosas Guías de Práctica Clínica para facilitar la identificación y correcto manejo de la patología tiroidea en la gestante. Esta proliferación de guías ha causado confusión al proponer distintos puntos de corte de valores de normalidad y distintas recomendaciones ante situaciones similares. Por ello, la Sociedad Española de Endocrinología y Nutrición y la Sociedad Española de Ginecología y Obstetricia han elaborado el presente Documento de Consenso, con el objetivo de crear un marco de actuación conjunto que unifique criterios de diagnóstico y tratamiento de la disfunción tiroidea en estas pacientes. El Documento se estructura respondiendo a las preguntas más frecuentes que se plantean en la práctica clínica, agrupándose en cinco apartados: 1/Valores de referencia de pruebas de función tiroidea y cribado durante la gestación 2/Nutrición de Yodo 3/Hipotiroidismo y gestación 4/Hipertiroidismo y gestación 5/ Autoinmunidad tiroidea.

Section snippetsIntroduction, methodology and objectives

Thyroid function disorders are very common in women of childbearing age. Given their association during pregnancy with multiple complications, both maternal and fetal, various clinical practice guidelines have been developed to help in the identification and correct management of thyroid disease in pregnant women. Over the last decade, the leading scientific societies have developed different guidelines: the American Thyroid Association (ATA) 2011, the Endocrine Society 2012, the European

What are normal values for thyroid function tests during pregnancy?

According to the 2017 ATA guide, whenever possible, thyroid-stimulating hormone (TSH) reference ranges should be defined based on the reference population and specific for each trimester. (Strong recommendation, moderate evidence.)1

If no own reference ranges are available, the ATA guideline places the upper limit of TSH in the first trimester at 4 mU/l.

What is the right time to screen pregnant women for thyroid dysfunction?

This cut-off point is valid when the TSH determination is performed between weeks seven and 12 of pregnancy. In Spain, given that the

What are the normal iodine requirements during pregnancy?

Iodine is an essential micronutrient vital for the synthesis of thyroid hormones, and the nutritional needs are increased during pregnancy.3

The WHO's recommended iodine intake is 250 μg/day. Likewise, it establishes a threshold of 500 μg/day, above which no additional benefits are achieved and it could even induce alterations in thyroid function. On the other hand, the Institute of Medicine in the USA sets the needs at 220 μg/day during pregnancy and 290 μg/day during lactation.4

Is its pharmacological supplementation recommended during pregnancy?

Nutritional

Is it necessary to carry out pre-pregnancy monitoring of women with known hypothyroidism?

Women with known hypothyroidism should plan their pregnancy to reduce the rate of complications. A TSH concentration of <2.5 mU/l is recommended. (Strong recommendation, moderate evidence.)1

Why is there a limit of 2.5 mU/l in pre-pregnancy hypothyroid women, when the cut-off point in euthyroid pregnant women is 4.0 mU/l? Because this ensures that the increased hormonal requirements of pregnancy can be met.

How should pregnant women with clinical hypothyroidism be managed? (Including those diagnosed prior to pregnancy)

Clinical hypothyroidism is associated with multiple maternal complications (miscarriage,

How to distinguish hyperemesis gravidarum/transient gestational hyperthyroidism from Graves' disease?

Nausea and vomiting are very common during the first trimester of pregnancy, but they are usually sporadic, of little relevance, and only a small percentage of women will develop hyperemesis gravidarum. Given that they present a low TSH, since its origin is related to a greater increase in ®-hCG, it must be distinguished from hyperthyroidism due to Graves' disease (GD). The clinical characteristics that help distinguish both conditions are listed in Table 7.

How is hyperemesis gravidarum/transient gestational hyperthyroidism managed?

Transient gestational hyperthyroidism

Thyroid autoimmunity and risk of miscarriage

It has been considered that the presence of thyroid autoimmunity is an independent risk factor for miscarriage,9 and there is debate about whether euthyroid pregnant women with positive anti-TPO should be treated with LT4. Table 5 summarises the possible options.

Thyroid autoimmunity and preterm birth

The association between thyroid autoimmunity and risk of preterm birth has been evidenced in different meta-analyses. However, the ATA guideline considers that there is not enough evidence to recommend treating euthyroid pregnant women

Conflicts of interest

The authors declare that they have no conflicts of interest.

Acknowledgements

The authors wish to thank Drs Elena Navarro, Juan Carlos Galofré, Mercè Albareda and Piedad Santiago for their contribution in reviewing this manuscript.

References (10)

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