Postpartum thyroiditis: the thyroid condition that affects around one in ten mothers

Postnatal recovery · Updated July 2026 · All articles

Postpartum thyroiditis is one of the more commonly missed postnatal conditions. It can cause symptoms ranging from heart palpitations and anxiety to overwhelming fatigue and low mood, yet because these overlap so closely with the normal experience of new parenthood, it is often attributed to exhaustion, stress, or postnatal depression rather than investigated as a thyroid problem. Knowing that it exists, and knowing what the symptoms look like, means you are better placed to ask for the right test if something feels off.

What is postpartum thyroiditis?

Postpartum thyroiditis is an autoimmune inflammation of the thyroid gland that develops in the first year after birth. The immune system, which modulates itself during pregnancy to prevent it from attacking the developing baby, rebounds after delivery. In some people, this immune rebound causes the immune system to mistakenly target the thyroid, leading to inflammation.

It is distinct from Hashimoto's thyroiditis, a longer-term autoimmune thyroid condition, though the two share some similarities. People who have thyroid antibodies in their blood before or during pregnancy are at higher risk of developing postpartum thyroiditis, as are those with a personal or family history of autoimmune conditions, including type 1 diabetes and other thyroid conditions. Overall, it affects an estimated 5 to 10 percent of new mothers, though milder cases may go undiagnosed.

The two phases: hyperthyroid and hypothyroid

Postpartum thyroiditis typically progresses through two phases, though not everyone experiences both. The classic pattern is an initial hyperthyroid phase followed by a hypothyroid phase, but some people have only one of the two.

The hyperthyroid phase occurs when the inflamed thyroid gland releases stored thyroid hormone into the bloodstream in excess. It usually begins around one to four months after birth and lasts for two to three months. During this phase, thyroid hormone levels are higher than normal and TSH (the pituitary hormone that regulates thyroid function) falls below the normal range.

The hypothyroid phase occurs when the thyroid, having depleted its hormone stores during the hyperthyroid phase, cannot produce sufficient new hormone. This phase typically begins around four to eight months after birth and can last for several months. TSH rises above the normal range as the pituitary gland tries to stimulate the underactive thyroid.

Symptoms of the hyperthyroid phase

During the hyperthyroid phase, high levels of thyroid hormone in the body cause the metabolism to speed up. You may notice palpitations or a racing heart, increased sweating, feeling warm or hot much of the time, unexplained weight loss despite eating normally, anxiety or feeling jittery, trembling hands, difficulty sleeping, or increased bowel movements. These symptoms can easily be mistaken for general postnatal anxiety, caffeine sensitivity, or just the stress of new parenthood.

It is worth noting that the hyperthyroid phase of postpartum thyroiditis is generally milder than Graves' disease, another cause of hyperthyroidism. It often does not require treatment and settles on its own as hormone levels normalise, though in some cases a beta-blocker may be prescribed to manage palpitations and anxiety symptoms while the body adjusts.

Symptoms of the hypothyroid phase

The hypothyroid phase is characterised by a slowed metabolism. Symptoms include profound fatigue that feels different from ordinary new-parent tiredness, low mood and depression, brain fog and difficulty concentrating, unexplained weight gain, feeling constantly cold, dry skin and hair, hair loss beyond normal postpartum shedding, constipation, and muscle aches. These symptoms bear a very strong resemblance to postnatal depression and are one of the key reasons that thyroid function tests are valuable in new mothers who present with low mood and fatigue that seems disproportionate or persistent.

If hypothyroidism is significant and symptomatic, treatment with levothyroxine (a synthetic thyroid hormone) is usually started. This is taken as a daily tablet and is safe during breastfeeding. Once treatment begins, symptoms typically improve over the following weeks.

How postpartum thyroiditis is diagnosed

Postpartum thyroiditis is diagnosed with a blood test. The most important measurement is TSH, the pituitary hormone that rises when thyroid output is too low and falls when thyroid hormone levels are too high. A full thyroid panel also includes T4 (thyroxine) and sometimes T3. Thyroid antibodies (specifically thyroid peroxidase antibodies) may also be tested, as their presence indicates an autoimmune process.

If you have symptoms in any of the clusters described above in the first year after birth, a thyroid function test is a simple and worthwhile step. The test is just a blood draw and can be requested by your GP at a routine appointment. You do not need a referral to a specialist to get the initial test.

If results are abnormal, your GP may refer you to an endocrinologist, or they may manage your treatment directly depending on the severity of the findings and local pathways.

Most cases resolve within a year

The good news for most people is that postpartum thyroiditis is self-limiting. Around 80 percent of those affected return to normal thyroid function within 12 to 18 months without long-term treatment. The inflammation resolves, and the thyroid recovers its normal output.

However, approximately 20 to 30 percent of people who experience the hypothyroid phase go on to develop permanent hypothyroidism that requires lifelong treatment. This is more likely in people who have higher levels of thyroid antibodies. For this reason, thyroid function should be rechecked periodically, particularly in people who have been treated for the hypothyroid phase, to confirm whether treatment can be withdrawn or needs to continue.

Risk in future pregnancies

If you have had postpartum thyroiditis, your risk of it recurring after a subsequent pregnancy is significantly elevated, with some estimates as high as 70 percent. This means it is important to let your midwife and GP know at the start of any future pregnancy, so that thyroid function can be monitored through the pregnancy and again in the postnatal period. Early detection and management in a subsequent episode can be straightforward once it is being looked for.

When to raise it with your GP

It is worth raising postpartum thyroiditis specifically if you have persistent symptoms in either of the clusters described above in the months after birth, particularly if symptoms of depression, anxiety, or fatigue are not responding as expected to support or treatment, or if you know you have thyroid antibodies or a history of autoimmune conditions. A simple blood test is all that is needed to investigate.

Frequently asked questions

What is postpartum thyroiditis?

Postpartum thyroiditis is an autoimmune inflammation of the thyroid gland that occurs in the first year after birth. It affects around 5 to 10 percent of new mothers and typically causes a hyperthyroid phase, a hypothyroid phase, or both.

How is postpartum thyroiditis diagnosed?

It is diagnosed with a blood test measuring TSH (thyroid stimulating hormone) and, usually, T4. A low TSH suggests hyperthyroidism; a high TSH suggests hypothyroidism. Your GP can arrange this test.

Does postpartum thyroiditis go away on its own?

In most cases, yes. Around 80 percent of people return to normal thyroid function within 12 to 18 months. However, about 20 to 30 percent develop permanent hypothyroidism and will need ongoing treatment.

Can postpartum thyroiditis cause postnatal depression?

The hypothyroid phase can cause low mood, fatigue, and brain fog that closely mimic postnatal depression. This is one of the reasons thyroid function is worth checking if postnatal depression symptoms do not respond as expected to treatment.

Will I get postpartum thyroiditis in my next pregnancy?

If you have had postpartum thyroiditis once, your risk of it recurring after subsequent pregnancies is significantly higher, around 70 percent. Your thyroid function should be monitored after any future births.

Is it safe to breastfeed with postpartum thyroiditis?

In most cases, yes. The most commonly used medications for postpartum thyroiditis are considered compatible with breastfeeding, but always discuss this with your GP or endocrinologist who can advise on your specific treatment.

This article is for general information only. Always speak to your midwife, GP, or health visitor if you have concerns about your physical recovery after birth.