Population: Women during and immediately after pregnancy with thyroid disease.

Organizations

ATA 2017, ACOG 2020

Recommendations

Evaluation

–Hypothyroidism in pregnancy is defined as:

• An elevated TSH (>2.5 mIU/L) and a suppressed free thyroxine (FT₄).

• TSH ≥10 mIU/L (irrespective of FT₄).

–If a thyroid nodule is found, arrange thyroid ultrasound and TSH testing.

Management

–Do not treat subclinical hypothyroidism (TSH 2.5–9.9 mIU/L and a normal FT₄) in pregnancy.

–If hypothyroid treat with levothyroxine, starting with 1–2 mcg/kg or 100 mcg daily. Goal of therapy is to normalize TSH levels (between lower limit of reference range and 2.5 mU/L). Monitor TSH levels every 4 wk when treating thyroid disease in pregnancy.

–Measure a TSH receptor antibody level at 20–24 wk for any history of Graves disease (GD).

–Patients found to have thyroid cancer during pregnancy would ideally undergo surgery during second trimester.

–Do not treat transient hCG-mediated TSH suppression in early pregnancy with antithyroid drug therapy.

–If hyperthyroid, use propylthiouracil (PTU) or methimazole. Avoid methimazole in the first trimester.

–Treat Graves disease during pregnancy with the lowest possible dose of antithyroid drug needed to keep the mother’s thyroid hormone levels at or slightly above the reference range for total T₄ and T₃ values in pregnancy (1.5 times above nonpregnant reference ranges in the second and third trimesters), and the TSH below the reference range for pregnancy.

–Pregnancy is a relative contraindication to thyroidectomy and should only be used when medical management has been unsuccessful or ATDs cannot be used.

Sources

–Thyroid. 2016;26(10):1343-1421.

–Thyroid. 2017;27(3):315-390.

–http://thyroidguidelines.net/sites/thyroidguidelines.net/files/file/thy.2011.0087.pdf

–Obstet Gynecol. 2020; 135(6):e261-e274.