Postpartum Thyroiditis

What is postpartum thyroiditis?

During pregnancy, the immune system is partly suppressed so the body does not reject the baby. After birth, it rebounds. In women who already have thyroid antibodies (often without knowing it), this rebound triggers an autoimmune attack on the thyroid, similar to Hashimoto's thyroiditis.

The inflamed thyroid first leaks its stored hormone into the blood, causing a temporary overactive phase. Once the store is used up and the gland is damaged, it underproduces, causing an underactive phase. As inflammation settles, the gland usually recovers.

The phases of postpartum thyroiditis

Only about a quarter of women go through both phases. About a third have only the hyperthyroid phase and about 4 in 10 only the hypothyroid phase.

Many symptoms overlap with normal life with a newborn, so postpartum thyroiditis is often missed.

Who is at risk?

• Positive thyroid peroxidase (TPO) antibodies before or during pregnancy (about 30 to 50% of these women develop it)
• Previous postpartum thyroiditis (up to 70% recurrence in later pregnancies)
• Type 1 diabetes
• Other autoimmune diseases, such as lupus
• Personal or family history of thyroid disease
• Chronic viral hepatitis

Postpartum thyroiditis vs Graves' disease

Both cause an overactive thyroid after pregnancy, but they need different treatment.

Radioactive iodine scans are avoided while breastfeeding, so doctors rely mainly on blood antibodies and ultrasound blood flow.

Diagnosis

• TSH: low in the hyperthyroid phase, high in the hypothyroid phase
• Free T4 (and sometimes T3): high, then low
• TPO antibodies: usually positive
• TSH receptor antibodies: to rule out Graves' disease
• Thyroid ultrasound: may show an inflamed gland with reduced blood flow

Some guidelines suggest checking TSH at 3 and 6 months after birth in women with type 1 diabetes or known TPO antibodies. Anyone with postpartum depression should have thyroid tests.

Treatment

Hyperthyroid phase

• Usually no treatment is needed if symptoms are mild.
• A beta-blocker such as propranolol eases palpitations, tremor and anxiety. Propranolol is generally considered compatible with breastfeeding at low doses.
• Antithyroid drugs do not help, because the gland is not overproducing.

Hypothyroid phase

• Levothyroxine (thyroid hormone replacement) is recommended if you have symptoms, are breastfeeding with symptoms, or are trying to get pregnant again, or if TSH is clearly raised (above about 10 mIU/L).
• It is safe while breastfeeding.
• Treatment is often tried for 6 to 12 months, then tapered to see whether the thyroid has recovered. It should not be stopped while trying to conceive or during pregnancy.

Long-term outlook

Most women's thyroid function returns to normal within a year to 18 months. However, about 20 to 50% develop permanent hypothyroidism within 5 to 10 years, especially those with high antibody levels or a severe hypothyroid phase. The American Thyroid Association recommends a yearly TSH test for life after an episode.

Planning another pregnancy

Postpartum thyroiditis often comes back after later pregnancies. Before trying to conceive, check TSH. Untreated hypothyroidism in pregnancy can affect the baby's development and raise the risk of miscarriage, so levothyroxine is adjusted to keep TSH in the target range.

Frequently asked questions

What are the symptoms of postpartum thyroiditis?

Early on, you may have palpitations, anxiety, irritability, trouble sleeping, shakiness and weight loss. Later, symptoms swing to tiredness, low mood, feeling cold, constipation, dry skin, hair loss and weight gain. Because these overlap with normal new-parent exhaustion, a simple blood test is the only reliable way to know.

How long does postpartum thyroiditis last?

The overactive phase usually lasts 1 to 3 months and the underactive phase up to 6 to 12 months. Most women recover normal thyroid function within 12 to 18 months of giving birth. Up to half develop permanent hypothyroidism years later, so yearly thyroid tests are recommended.

Can postpartum thyroiditis cause depression?

Yes. Both phases can affect mood, and the hypothyroid phase in particular is linked to low mood, fatigue and poor concentration. Thyroid problems can worsen or mimic postpartum depression, so anyone with postpartum depression should have a thyroid blood test. Treating hypothyroidism may improve mood.

Can I breastfeed with postpartum thyroiditis?

Yes. Postpartum thyroiditis does not prevent breastfeeding. Levothyroxine and low-dose propranolol are considered compatible with breastfeeding. Radioactive iodine scans and treatment are avoided while breastfeeding. Tell your doctor you are breastfeeding before any test or medicine.

Will postpartum thyroiditis come back in future pregnancies?

It often does. Up to 70% of women who had it once get it again after a later pregnancy, especially if they still have thyroid antibodies. Check your TSH before trying to conceive, during pregnancy as advised, and in the months after birth.