The Endocrine Society has just made revisions to its Clinical Practice Guideline (CPG) for management of thyroid disease during pregnancy and postpartum. Having too little or too much of throid hormones can impact both mother and fetus. Hypothyroid women (too low thyroid) are more likely to experience infertility and have an increased prevalence of anemia, gestational hypertension and postpartum hemorrhage. If left untreated, maternal hypothyroidism is associated with premature birth, low birth-weight and neonatal respiratory distress. Higher than normal thyroid hormone levels are associated with increased fetal loss.
Revisions from the CPG include:
Caution should be used in the interpretation of serum free thyroxine (T4) levels during pregnancy and each laboratory should establish trimester-specific reference ranges for pregnant women using a free T4 assay. The non-pregnant total T4 range (5-12 μg/dL – 50-150 nmol/L) can be adapted in the second and third trimesters by multiplying this range by 1.5-fold. Alternatively, the free T4 index appears to be a reliable assay during pregnancy;
Propylthiouracil (PTU), if available, should be the first-line drug for treatment of hyperthyroidism during the first trimester of pregnancy, because of the possible association of methimazole (MMI) with congenital abnormalities. MMI may also be prescribed if PTU is not available or if a patient cannot tolerate or has an adverse response to PTU. Recent analyses by the FDA indicate that PTU may rarely be associated with severe liver toxicity. For this reason, clinicians should change treatment of patients from PTU to MMI after completion of the first trimester;
Breastfeeding women should maintain a daily intake of 250 μg of iodine to ensure breast-milk provides 100 mcg iodine per day to the infant;
Once-daily prenatal vitamins should contain 150-200μg iodine and that this be in the form of potassium iodide or iodate, the content of which is verified to insure that all pregnant women taking prenatal vitamins are protected from iodine deficiency;
Since thyroid receptor antibodies (thyroid receptor stimulating, binding, or inhibiting antibodies) freely cross the placenta and can stimulate or inhibit the fetal thyroid, these antibodies should be measured before 22 weeks gestational age in mothers with 1) current Graves’ disease or 2) a history of Graves’ disease and treatment with 131-I or thyroidectomy before pregnancy, or 3) a previous neonate with Graves’ disease or 4) previously elevated TSH receptor antibodies (TRAb);
In women with TRAb at least 2-3 fold the normal level, and women treated with anti-thyroid drugs, fetal thyroid dysfunction should be screened for during the fetal anatomy ultrasound (18-22nd weeks) and repeated every 4-6 weeks or as clinically indicated. Evidence of fetal thyroid dysfunction could include thyroid enlargement, growth restriction, hydrops, presence of goiter, advanced bone age, or cardiac failure.
Women with nodules 5 mm-1cm 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 1.5-2 cm should also receive an FNA.
During the last 6 weeks of pregnancy, FNA can reasonably be delayed until after delivery. Ultrasound guided FNA is likely to have an advantage for maximizing adequate sampling.
The committee that developed the CPG could not reach agreement on screening recommendations for all newly pregnant women:
- Some members recommend screening of all pregnant women for serum TSH abnormalities by the 9th week or at the time of their first visit.
- Other members recommend neither for nor against universal screening of pregnant women at the time of their first visit and support aggressive case finding to identify and test high-risk women. In some situations, ascertainment of an individual’s risk status may not be feasible and in such cases, testing of all women by 9 weeks of pregnancy or at the first prenatal visit is reasonable.
Source: “Management of Thyroid Dysfunction during Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline” in Journal of Clinical Endocrinology and Metabolism (JCEM), 2012