Postpartum Thyroiditis

Postpartum thyroiditis is autoimmune inflammation of the thyroid within the first year after birth, causing a thyrotoxic phase, a hypothyroid phase or both. It affects 5 to 10 percent of women, and more in those with type 1 diabetes or thyroid peroxidase antibodies. It matters because the symptoms are mistaken for normal tiredness or depression, and hypothyroidism may persist in up to 20 to 30 percent of women.

• Risk factors: positive thyroid peroxidase antibodies, type 1 diabetes, previous postpartum thyroiditis, other autoimmune disease, family history of thyroid disease.
• Thyrotoxic phase at 1 to 4 months, hypothyroid phase at 4 to 8 months, recovery by 12 months.
• Some women have only the thyrotoxic phase, some only the hypothyroid phase and some both.

The thyrotoxic phase causes palpitations, anxiety, irritability, heat intolerance, tremor, weight loss and tiredness, usually mild. The hypothyroid phase causes fatigue, cold intolerance, constipation, dry skin, weight gain, poor memory, low mood and a small painless goitre.

• Small, firm, painless goitre is common.
• Tachycardia and tremor in the thyrotoxic phase; slow pulse and delayed reflexes in the hypothyroid phase.
• Differential diagnosis: Graves disease, postpartum depression, anaemia, Sheehan syndrome, subacute thyroiditis, toxic nodule, anxiety, normal postpartum tiredness, peripartum cardiomyopathy, hyperemesis related thyrotoxicosis.
• Complications: persistent hypothyroidism, depression, poor lactation, recurrence after later pregnancies, infertility, miscarriage in later pregnancy.

The approach is thyroid function testing at the right time with tests to separate Graves disease.

• Thyroid stimulating hormone and free thyroxine (low TSH with high free T4 in the thyrotoxic phase; high TSH with low free T4 in the hypothyroid phase); free T3 if needed.
• Thyroid peroxidase antibodies (positive in most women); TSH receptor antibodies to exclude Graves disease; raised ESR is not typical.
• Thyroid ultrasound (diffuse hypoechoic gland with low flow); radioiodine uptake is avoided in breastfeeding.
• Full blood count, glucose, and screening for depression using a standard questionnaire.

The principle is symptom control in the thyrotoxic phase without antithyroid drugs, levothyroxine for symptomatic hypothyroidism, and monitoring for permanent hypothyroidism.

• Supportive: reassurance that thyrotoxicosis is temporary; adequate dietary iodine (about 250 micrograms daily during lactation) while avoiding excess iodine such as kelp supplements; rest; treat anaemia; continue breastfeeding.
• Pharmacological: thyrotoxic phase with symptoms: propranolol 20 to 40 mg oral 8-hourly (maximum 160 mg daily), reduced as symptoms settle; antithyroid drugs are not used because the thyroid is leaking stored hormone; hypothyroid phase with symptoms, TSH above 10 mU/L, breastfeeding or planned pregnancy: levothyroxine 50 micrograms oral once daily on an empty stomach, increased by 25 micrograms every 4 to 6 weeks to normalise TSH (usual dose 1.6 micrograms/kg/day), for 6 to 12 months then withdrawn with a TSH check at 6 weeks; subclinical hypothyroidism without symptoms: monitoring only, unless pregnancy is planned or TSH is above 10 mU/L.
• Procedures: none.
• Special groups: women with type 1 diabetes have glucose checks and insulin adjustment during thyrotoxic and hypothyroid phases; women planning pregnancy continue levothyroxine to keep TSH below 2.5 mU/L; breastfeeding is compatible with propranolol and levothyroxine.
• Red flags: heart rate above 120 per minute, atrial fibrillation, fever with agitation and confusion, severe depression or psychosis, goitre with pain, stridor, weight loss above 5 kg, features of Graves disease (eye signs, high TSH receptor antibodies).
• Follow-up: TSH and free T4 every 6 to 8 weeks during active disease; after stopping levothyroxine at 12 months, TSH at 6 weeks and then yearly for life because of the risk of permanent hypothyroidism; thyroid tests before and early in any later pregnancy.