What postpartum thyroiditis is

It is an autoimmune inflammation of the thyroid gland that starts in the year after birth. The RCOG describes it as "an autoimmune inflammation of your thyroid gland. It can happen in the 12 months after you have given birth."

The British Thyroid Foundation adds the numbers and the nature of it: "Postpartum thyroiditis is a temporary, inflammatory condition that occurs in less than 1 in 10 pregnancies. It is more common in women who have thyroid autoantibodies. This condition normally shows up in the first 12 months after birth."

Less than 1 in 10 makes it far from rare, and it is one of the more plausible explanations for symptoms that get filed under "just being a new parent".

The two phases, and why they confuse everyone

Postpartum thyroiditis typically runs in two stages that pull in opposite directions.

The British Thyroid Foundation: "It usually starts off with symptoms of hyperthyroidism (weight loss, anxiety, heat intolerance, tremor) and you may have a painless lump in your neck. This is followed by symptoms of hypothyroidism (feeling tired, low mood, cold)."

Not everyone gets both phases, and some people get neither in a form they notice. The RCOG: "Sometimes you may not have any symptoms."

The overactive phase

The NHS lists the symptoms of an overactive thyroid as nervousness, anxiety and irritability, mood swings, difficulty sleeping, persistent tiredness and weakness, sensitivity to heat, swelling in the neck from an enlarged thyroid gland, an irregular or unusually fast heart rate, twitching or trembling, and weight loss.

Read that list again with a newborn in mind. Anxious, irritable, not sleeping, exhausted, sweating, heart racing, losing weight. Every single symptom has an obvious non-thyroid explanation in the first months after a birth, which is exactly why this is missed.

The underactive phase

The NHS lists hypothyroid symptoms as feeling extremely tired, feeling cold more than usual, putting on weight, constipation, difficulty concentrating or thinking clearly, low mood or depression, dry skin, dry hair or hair loss, a croaky voice, and irregular or heavy periods.

The overlap with postnatal depression is close to total, and it is the reason this page exists.

The overlap with postnatal depression

The RCOG builds this into its guidance. It says you should have your thyroid function checked if you have symptoms of hyperthyroidism, hypothyroidism, or "severe postnatal depression".

That is not a suggestion that thyroid disease explains away postnatal depression. Postnatal depression is common, real, and treatable in its own right, and it affects 10 to 15 in every 100 women. But a thyroid blood test is cheap, quick and answers a question that is otherwise very hard to answer from symptoms alone.

Who is more likely to get it

The British Thyroid Foundation says it is more common in women who have thyroid autoantibodies. The RCOG adds that it is "more common if you have other autoimmune conditions or a family history of thyroid problems." The NHS notes that when assessing possible hypothyroidism a GP will ask about family history of thyroid or autoimmune conditions "or if you've recently been pregnant."

When to call

Book a GP appointment if:

you are unusually anxious, shaky, hot, or your heart is racing, and you are losing weight without trying
you are exhausted, cold, low, constipated and foggy in a way that is not improving
you have a painless swelling or lump in your neck
you have symptoms of postnatal depression, particularly if they are severe — the RCOG recommends thyroid testing in this situation
you have another autoimmune condition, or a family history of thyroid disease, and you feel unwell

The HSE mentions the same test in a different context: for postnatal hair loss, "your GP may suggest doing blood tests to check your iron and thyroid levels."

What testing involves

A blood test measuring thyroid-stimulating hormone (TSH) and thyroxine (T4), as the NHS describes for suspected hypothyroidism.

The British Thyroid Foundation is candid about who should be tested: "It is not recommended that your doctor tests for this unless you have risk factors e.g. thyroid autoantibodies, or have symptoms of thyroid disease." In other words, this is not a routine screen for everyone after birth — which is precisely why describing your symptoms clearly matters.

It also sets out what should happen if the first test is normal but symptoms persist: "your doctor should do a blood test to check your thyroid levels every 6-8 weeks and also check your symptoms." If levels later go out of range, TRAb antibody testing or an isotope scan may be used to distinguish postpartum thyroiditis from Graves' disease. A single normal result is not the end of the conversation if you still feel unwell.

Treatment, and how it usually ends

Often, no treatment at all. The British Thyroid Foundation says the condition "does not require treating with antithyroid drugs", and the RCOG that "treatment depends on your symptoms and you may not need anti-thyroid tablets. Postpartum thyroiditis usually gets better by itself."

If the underactive phase causes real symptoms, levothyroxine may be prescribed. The BTF: "Most women can stop taking these after 6 to 12 months. Around 1 in 3 women will need to take levothyroxine long-term." That last figure is worth knowing in advance, so that needing ongoing treatment does not feel like something has gone wrong.

Follow-up matters more here than in most postnatal conditions. The RCOG: "you might develop hypothyroidism in the future. You should have your thyroid function checked every year and at the start of any future pregnancies." The NHS reinforces the pregnancy part — if you have an underactive thyroid and are pregnant or planning to be, tell your GP, because your dose is likely to need changing and untreated hypothyroidism raises the risk of complications including pre-eclampsia.

What to let go of

Feeling wrung out in the months after a birth does not mean you have a thyroid problem — most people who feel this way do not. But if the symptoms are extreme, one-sided (all heat and racing heart, or all cold and fog), come with a neck swelling, or sit alongside severe low mood, a blood test is a reasonable ask. The RCOG has written it into its patient guidance, so you are not asking for anything unusual.

Postpartum Thyroiditis