Updated evidence-based recommendations from the American Thyroid Association (ATA) provide guidance on how best to diagnose and manage thyroid dysfunction during pregnancy, especially mild or “subclinical” hypothyroidism.1 The guidelines offer specific treatment recommendations for various levels of thyroid dysfunction and targets for therapy.

“The new guidelines …  make it clear[er] when intervention for thyroid-related problems is more likely to impact the course and outcome of the pregnancy and outline more clearly how the intervention should be applied,” said ATA President John C. Morris, III, MD, from the Mayo Clinic in Rochester, Minnesota in an email interview with Endocrinology Advisor.

Pregnancy has a profound effect on thyroid gland function, and thyroid disease is common in pregnancy, with an estimated 300,000 pregnancies affected by thyroid disease in the United States annually.2 Yet, there is considerable debate over the optimal treatment of hyperthyroidism during pregnancy.

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“The 97 recommendations presented in the new Guidelines help define current best practices for thyroid function testing, iodine nutrition, pregnancy complications, and treatment of thyroid disease during pregnancy and lactation,” according to an ATA news release.2 The authors stated that there is insufficient evidence to recommend for or against universal screening for abnormal thyroid-stimulating hormone (TSH) concentrations in early pregnancy or preconception. However, TSH screening is recommended for women planning assisted reproduction or those known to have positive thyroid autoantibodies.

The ATA guidelines were first published in 2011.3 Since that time, significant clinical and scientific advances have occurred in the field, with the authors noting a substantial amount of new literature within the last 5 years.

The updated guidelines include recommendations related to the diagnosis and management of hypothyroidism, thyrotoxicosis, thyroid nodules, and thyroid cancer, as well as thyroid considerations in infertile women and fetal and neonatal considerations. One recommendation (number 29) gives specific advice regarding levels of thyroid test results that can be applied to the patient in the clinic setting when making decisions about intervention. It recommends that subclinical hypothyroidism in pregnancy be approached on the basis of several factors.

The authors wrote that levothyroxine therapy may be considered for thyroid peroxidase antibody (TPO) antibody-positive women with TSH concentrations greater than the pregnancy specific reference range, or when TSH >2.5 mU/L but below the upper limit of the pregnancy-specific reference range. This approach is also recommended for TPO antibody-negative women with TSH concentrations greater than the pregnancy-specific reference range and <10.0 mU/L.

The authors do not recommend levothyroxine therapy for TPO antibody-negative women with a normal TSH (TSH within the pregnancy-specific reference range, or <4.0 mU/L if unavailable).

“Perhaps the most important portions of these guidelines are those describing the diagnosis and management of thyroid dysfunction during pregnancy, especially mild or ‘subclinical’ hypothyroidism. The guidelines give treatment recommendations for various levels of thyroid dysfunction and targets for therapy that when applied can favorably affect the course of pregnancy and health and well-being of the mother and baby,” Dr Morris told Endocrinology Advisor.

Dr Morris said the guidelines were produced by an international panel of recognized experts and can serve as the gold standard for diagnosis and management of thyroid disorders in pregnancy. The task force noted that it often struggled with the paucity of high-quality double-blinded placebo-controlled trials investigating thyroid conditions during pregnancy.

The authors reported that only a minority of the nearly 100 recommendations in the present guidelines were graded at the highest American College of Physicians Grading System level of evidence. They recommended conducting a study that evaluates the effect of iodine supplementation in pregnant women with the mildest form of iodine deficiency (median urinary iodine concentrations, 100 to 150 μg/L). They also recommended investigators conduct a randomized controlled trial of early levothyroxine intervention (at 4 to 8 weeks of pregnancy) in women with either subclinical hypothyroidism or isolated hypothyroxinemia to determine effects on child IQ.

Summary and Clinical Applicability

Perinatologist Amy Valent, DO, an assistant professor of obstetrics and gynecology at Oregon Health & Science University School of Medicine in Portland, said that at this time, there are significant limitations to making solid recommendations for care during pregnancy, as quality, prospective thyroid studies are a challenge to perform. However, Dr Valent said the new guidelines are an excellent summary of the current published data and they have made the recommendations clearer for management in pregnancy.

“I think what is still needed in the literature for the guidelines are studies regarding antithyroid antibody testing for women with [a] history of preterm birth. Studies have reported antibodies are associated with preterm birth. Unfortunately, there are not enough data to support treatment with levothyroxine among women who have antibodies but have normal TSH levels nor to support checking antibodies in women with a history of preterm birth,” she told Endocrinology Advisor.

Dr Valent said preterm birth causes significant morbidity and mortality and the link with thyroid disease is understudied.


Dr Morris and Dr Valent have disclosed no relevant financial relationships concerning their comments.

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  1. Alexander EK, Pearce EN, Brent GA, et al. 2017 guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum [published online January 6, 2017]. Thyroid. doi: 10.1089/thy.2016.0457
  2. American Thyroid Association guidelines for diagnosis and management of thyroid disease during pregnancy published in Thyroid journal [news release]. Falls Church, VA: American Thyroid Association; January 15, 2017. http://www.thyroid.org/association-guidelines-management. Accessed February 13, 2017.
  3. Stagnaro-Green A, Abalovich M, Alexander E, et al; for the American Thyroid Association Taskforce on Thyroid Disease During Pregnancy and Postpartum. Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011;21(10):1081-1125. doi: 10.1089/thy.2011.008y

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