Thyroid Nodule in Pregnancy

Thyroid nodule in pregnancy is a discrete lump in the thyroid found by palpation or ultrasound. Most are benign colloid nodules, but a minority are cancer, mostly papillary. It matters because evaluation must avoid radioiodine, and surgery, if needed, is timed to the second trimester.

• Nodules grow in pregnancy under hCG and iodine deficiency.
• Radioactive iodine and radionuclide scans are contraindicated.
• Most thyroid cancers in pregnancy have good outcomes with timely care.

Women have a neck lump, sometimes with hoarseness, difficulty swallowing or neck pain; most have none. Examine thyroid and cervical nodes.

• Hard, fixed nodule with node enlargement is suspicious.
• Rapid growth, voice change and stridor suggest cancer.
• Differential diagnosis: benign colloid nodule, thyroid cyst, multinodular goitre, thyroiditis, papillary thyroid cancer, medullary cancer, parathyroid lesion.
• Complications: compression, hyperthyroidism, malignancy, metastasis, surgical complications.

The approach is ultrasound with thyroid function and fine needle aspiration for suspicious nodules.

• TSH and free T4 (if TSH is low a toxic nodule is likely and no biopsy is needed).
• Neck ultrasound: size, solid or cystic, microcalcifications, irregular margins, taller than wide shape, nodes.
• Fine needle aspiration for nodules of 1 cm or above with suspicious features, or 2 cm or above in any nodule; cytology categories guide care.
• Serum calcitonin if medullary cancer is suspected; avoid radionuclide scan.

The principle is to find cancer early, defer surgery to the second trimester or after delivery, and avoid radiation.

• Supportive: reassure for benign nodules; avoid iodine excess; teach to report growth or voice change; iodised salt.
• Pharmacological: no drug for benign nodules; levothyroxine suppression is not used; if hyperthyroid give propylthiouracil 100 mg oral 8-hourly in the first trimester, then carbimazole 10 to 20 mg oral daily after 16 weeks, adjusted to keep free T4 at the upper limit of normal; for confirmed papillary cancer detected before 24 weeks give levothyroxine 1.6 to 2.0 micrograms/kg oral daily to keep TSH at 0.1 to 1.0 mIU/L while waiting; after thyroidectomy give levothyroxine 1.6 to 2.0 micrograms/kg oral daily and calcium carbonate 1 g oral 8-hourly if hypocalcaemic.
• Procedures: fine needle aspiration under ultrasound; hemithyroidectomy or total thyroidectomy in the second trimester for rapidly growing cancer, medullary cancer or anaplastic cancer; otherwise delay surgery until after delivery; radioactive iodine is given only after delivery and after stopping breastfeeding.
• Special groups: medullary or anaplastic cancer needs urgent surgery at any gestation; women with a family history of multiple endocrine neoplasia need calcitonin and metanephrines before surgery.
• Red flags: rapid growth, hoarseness, stridor, dysphagia, hard fixed nodule, nodes in the neck, raised calcitonin.
• Follow-up: repeat ultrasound every 4 to 6 weeks if cancer is not yet treated; TSH every 4 weeks; thyroid review at 6 weeks postpartum.