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In Brief

Clinical news

New guidelines for thyroid disease in pregnancy

By Jane Lewis
The American Thyroid Society has released 2017 guidelines for the diagnosis and management of thyroid disease during pregnancy and postpartum. The guidelines include 97 recommendations spanning several areas, including screening in pregnancy; interpreting tests; management of hypothyroidism, hyperthyroidism, thyroid nodules and cancer in pregnancy; thyroid disease and lactation, and more.

‘These evidence-based, comprehensive guidelines provide authoritative practical assistance,’ commented Professor Duncan Topliss, Director of the Department of Endocrinology and Diabetes at The Alfred, Melbourne. ‘There are, nevertheless, still significant areas of uncertainty.’

Screening for abnormal thyroid levels in pregnant women is still not recommended, but the recommended case-finding criteria are ‘quite broad,’ he noted, and include being aged over 30 years, having had two or more pregnancies, having a personal or family history of autoimmune thyroid disease, and residing in even a moderately iodine-deficient area.

The guidelines recommend that pregnant and breastfeeding women ingest approximately 250 μg of dietary iodine daily, therefore they, and women planning pregnancy, should take a daily supplement containing 150 μg iodine (as potassium iodide).

Maternal hypothyroidism is now defined as a thyroid stimulating hormone (TSH) level elevated beyond the upper limit of the pregnancy-specific reference range (when not available, an upper reference limit of about 4.0 mU/L may be used). Women who are hypothyroid and taking levothyroxine (LT4) who become pregnant should independently increase their dose of LT4 by 20 to 30% and urgently notify their GP for testing and further evaluation.

Overt maternal hypothyroidism should be treated with oral LT4, with the target TSH in the lower half of the trimester-specific reference range. For subclinical hypothyroidism, LT4 treatment should be given to women who are thyroid peroxidase antibody positive with a TSH greater than the pregnancy-specific reference range. Recommended monitoring in pregnancy of overt and subclinical hypothyroidism and in those at risk for hypothyroidism is a serum TSH measurement approximately every four weeks until mid-gestation, and at least once near 30 weeks’ gestation. 

In hyperthyroidism, it is recommended in the guidelines that consideration be given to ceasing all antithyroid medication in newly-pregnant women with Graves’ disease who are euthyroid on a low dose of carbimazole or propylthiouracil (PTU). Regular thyroid function testing and clinical examination should then be conducted to assess maternal and fetal thyroid status.

‘There is now evidence for teratogenicity of both carbimazole and PTU,’ commented Professor Topliss. Since its teratogenic effects appear less severe, PTU is the treatment of choice through to 16 weeks of pregnancy.

Fine needle biopsy (FNB) is recommended for newly detected thyroid nodules in pregnant women with a nonsuppressed TSH, with its timing influenced by the clinical assessment of cancer risk. Papillary thyroid carcinoma detected in early pregnancy should be monitored sonographically, and surgery considered if there is substantial growth before 24 to 26 weeks’ gestation, or if cytologically malignant cervical lymph nodes are present.
Thyroid 2017; doi: 10.1089/thy.2016.0457.

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