The guidelines for the management of thyroid disease during pregnancy and after birth has been recently updated from its earlier version. The clinical practice guideline, published in the Journal of Clinical Endocrinology and Metabolism, recommend approaches to diagnosing and treating patients with thyroid-related medical issues before, during, and immediately after pregnancy.
Thyroid function tests change during pregnancy due to the influence of two main hormones: human chorionic gonadotropin (hCG), the hormone that is measured in the pregnancy test and estrogen, the main female hormone. For the first 10-12 weeks of pregnancy, the baby is completely dependent on the mother for the production of thyroid hormone. By the end of the first trimester, the baby’s thyroid begins to produce thyroid hormone on its own. The baby, however, remains dependent on the mother for ingestion of adequate amounts of iodine, which is essential to make the thyroid hormones.
The new clinical guidelines include:
- Trimester-specific reference ranges for pregnant women, using a free T4 assay. “The non-pregnant total T4 range (5–12 μg/dL or 50–150 nmol/liter) are to be adapted in the second and third trimesters by multiplying this range by one and a half-fold. For more, click here.
- Propylthiouracil (PTU) should be the first-line drug for treatment of hyperthyroidism during the first trimester of pregnancy. Methimazole (MMI) may also be prescribed if PTU is not available or not tolerated. Clinicians should change treatment of patients from PTU to MMI after completion of the first trimester because of the potential for liver toxicity.
- Breast-feeding mothers should maintain a daily intake of 250 μg iodine to ensure breast-milk provides 100 mg iodine per day to the infant.
- One-daily prenatal vitamin containing 150 to 200 μg iodine needs to be consumed in the form of potassium iodide or iodate, to protect from iodine deficiency.
- Thyroid receptor antibodies need to be measured before 22 weeks’ gestational age in mothers with “1) current Graves’ disease; or 2) a history of Graves’ disease and treatment with or thyroid-ectomy before pregnancy; or 3) a previous neonate with Graves’ disease; or 4) previously elevated [thyroid-stimulating hormone receptor antibodies (TRAb)],” according to authors of the study.
- Regular Fetal Screening: In women with TRAb at least 2- to 3-fold the normal level, and women treated with anti-thyroid drugs, fetal thyroid dysfunction should be screened for during the fetal anatomy ultrasound done in the 18th–22nd week and repeated every four to six weeks or as clinically indicated. Evidence of fetal thyroid dysfunction could include thyroid enlargement, growth restriction, hydrops, presence of goiter, advanced bone age, tachycardia, or cardiac failure.
- Women with nodules from 5 mm to 1 cm in size should be considered for fine-needle aspiration (FNA) if they have a high risk history or suspicious findings on ultrasound, and women with complex nodules from 1.5 to 2 cm in size should also receive an FNA. “During the last weeks of pregnancy, FNA can reasonably be delayed until after delivery. Ultrasound-guided FNA is likely to have an advantage for maximizing adequate sampling,” according to the study. In an FNA, a very fine, thin needle is inserted into the thyroid, and aspirates (or “suctions”) cells and/or fluid from a thyroid nodule or mass into the needle. The sample obtained can then be evaluated for the presence of cancerous cells.
The committee could not reach a consensus on screening recommendations for all newly pregnant women. Some members recommended screening of all pregnant women for serum TSH abnormalities by the ninth week or at the time of their first visit.
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