The short answer: Postpartum thyroiditis is a painless, autoimmune inflammation of the thyroid that starts in the first year after giving birth. It often causes a short overactive phase, then an underactive phase. Most women get normal thyroid function back, but a meaningful minority stay hypothyroid, so follow-up blood tests matter even after you feel better.
What exactly is postpartum thyroiditis?
The 2017 American Thyroid Association (ATA) pregnancy guideline defines it as thyroid dysfunction in the first postpartum year in a woman whose thyroid was normal before pregnancy. Graves' disease is excluded from the definition. The guideline calls it an inflammatory autoimmune condition.
During pregnancy, the immune system is partly held back. After delivery, it rebounds. In women who already carry thyroid antibodies, that rebound can attack the thyroid. According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the inflammation makes stored thyroid hormone leak out of the gland. That leak is what drives the first phase.
It is common. The ATA guideline puts the prevalence at about 5%, with studies ranging from 1.1% to 16.7%. NIDDK describes it as affecting about 1 in 20 women in the first year after birth.
What happens in the overactive and underactive phases?
The classic pattern has two steps. First, leaked hormone raises blood levels (thyrotoxicosis). Then the damaged gland cannot keep up, and levels fall (hypothyroidism).
- Thyrotoxic phase: per the ATA guideline, it typically appears 2 to 6 months after delivery, though cases have been seen as late as a year. Every episode of this phase resolves on its own.
- Hypothyroid phase: it occurs from 3 to 12 months after delivery.
Not everyone goes through both. The guideline reports that about one quarter of patients have the classic two-phase form. Another quarter have only the overactive phase. About half have only the underactive phase. The ATA patient page gives a rougher split, so treat these numbers as estimates, not fixed rules.
Symptoms are often mild. In the overactive phase, the guideline lists irritability, heat intolerance, fatigue, and palpitations. Many women have no symptoms at all in this phase. The underactive phase is more often noticed, with cold intolerance, dry skin, fatigue, trouble concentrating, and tingling in the hands or feet.
Because new parents are tired and sleep-deprived anyway, these signs are easy to dismiss. NIDDK notes the underactive phase can be mistaken for the "baby blues."
Does postpartum thyroiditis go away on its own?
Often, yes, but not always. The overactive phase always clears without treatment. The underactive phase is where outcomes split.
The ATA guideline states that 10% to 20% of cases end in permanent hypothyroidism. It also flags a prospective study with a higher figure. In that study of 4,394 women in southern Italy, 169 developed postpartum thyroiditis (3.9%). Of those 169, 82% had a hypothyroid phase, and 54% were still hypothyroid at the end of the first postpartum year.
Recovery is also not always the end of the story. Across seven long-term studies reviewed in the guideline, 10% to 50% of women whose hypothyroid phase first resolved later developed permanent hypothyroidism. Factors linked to higher risk include:
- Higher TPO antibody levels
- A more severe initial hypothyroid phase
- Older maternal age and having had more children
- A low-echo (hypoechoic) thyroid on ultrasound
- A history of pregnancy loss
For this reason, the guideline recommends a yearly TSH test for any woman with a past episode of postpartum thyroiditis. Our guide to thyroid blood tests explains what TSH and free T4 results mean.
Who is most likely to get it?
Thyroid antibodies are the strongest single clue. The ATA guideline reports that women who test positive for thyroid antibodies in the first trimester have a 33% to 50% risk of postpartum thyroiditis. The higher the antibody level, the higher the risk. Read more about what TPO antibodies mean for hypothyroidism risk.
Other autoimmune conditions also raise the odds. The guideline lists these figures:
- Type 1 diabetes: 3 to 4 times the rate of the general population
- Chronic viral hepatitis: 25%
- Systemic lupus erythematosus: 14%
- Prior Graves' disease: 44%
It also tends to come back. Per the guideline, women who recover fully have a 70% chance of it returning with each later pregnancy. Women already on levothyroxine for Hashimoto's can still develop it if some working thyroid tissue remains.
Prevention options are limited. The guideline says giving levothyroxine or iodine to antibody-positive pregnant women does not prevent it. It also found the evidence too thin to recommend selenium.
How is postpartum thyroiditis treated?
Treatment depends on the phase and on how much the symptoms bother you. The ATA guideline gives these recommendations:
- Overactive phase: antithyroid drugs (methimazole and PTU) are not recommended. The gland is leaking stored hormone, not making extra, so these drugs do not help. If symptoms are significant, a beta-blocker that is safe while breastfeeding, such as propranolol or metoprolol, can be used at the lowest dose that works. Therapy usually lasts a few weeks.
- Watching for the next phase: after the overactive phase ends, TSH should be checked in about 4 to 8 weeks, or sooner if new symptoms start.
- Underactive phase: levothyroxine should be considered for women with symptoms. It should be started in women who are breastfeeding or trying to get pregnant. If no treatment is started, TSH should be repeated every 4 to 8 weeks until it normalizes.
- Stopping treatment: the guideline suggests attempting to stop levothyroxine after about 12 months, with a gradual taper and TSH checks every 6 to 8 weeks. Tapering should be avoided during pregnancy or while actively trying to conceive.
The overactive phase must be told apart from Graves' disease, which does need antithyroid drugs. Timing helps: thyrotoxicosis in the first 3 months after birth is more often thyroiditis. TSH receptor antibodies are usually positive in Graves' disease and negative in postpartum thyroiditis. If you are on levothyroxine and wondering about the trial off, see whether you can stop taking levothyroxine.
Is postpartum thyroiditis linked to postpartum depression?
The research is mixed. The ATA guideline describes studies on postpartum thyroiditis and depression as inconsistent. Two studies found a link between thyroid antibodies and depression regardless of thyroid levels. Another found no link. A trial of levothyroxine versus placebo in antibody-positive postpartum women showed no difference in depression rates.
Even so, the guideline makes a strong recommendation: everyone with depression, including postpartum depression, should be screened for thyroid problems. NIDDK also advises talking with your doctor soon if you develop postpartum depression or thyroid-type symptoms in the months after birth. If low mood is the main concern, depression.md covers screening and treatment options for depression.
The bottom line
Postpartum thyroiditis affects about 1 in 20 women and usually starts within a few months of delivery. The overactive phase always resolves on its own, and many women recover fully. But 10% to 20% end up with permanent hypothyroidism, and one large study found 54% still hypothyroid at one year. If you have thyroid antibodies, type 1 diabetes, or a past episode, ask for thyroid testing after delivery and a yearly TSH afterward.
Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. If you have symptoms after giving birth, talk with your doctor or endocrinologist about thyroid testing and treatment.