Postpartum thyroiditis affects 5–10% of women after birth and is consistently misdiagnosed as postnatal depression or tiredness. Here's the two-phase pattern, the symptoms to watch for, and how a TSH blood test diagnoses it.
Postpartum thyroiditis (PPT) is an autoimmune inflammation of the thyroid gland that occurs within the first year after birth. It affects approximately 5–10% of women — that's potentially 35,000–70,000 UK births per year producing cases. Recurrence rates approach 70% in subsequent pregnancies.
It has no dedicated NHS.uk page. It has no entry on Tommy's. There is no NCT resource for it. The clinical literature repeatedly notes that its symptoms are misattributed to 'normal postpartum experience' or misdiagnosed as postnatal depression.
If you have been feeling significantly more unwell than new parenthood alone seems to explain — particularly fatigue, mood changes, palpitations, or weight changes — this guide is worth reading.
Postpartum thyroiditis typically moves through two phases, though not every woman experiences both:
Phase 1: Hyperthyroid (roughly 1–4 months postpartum)
The inflamed thyroid releases excess stored hormone. Symptoms: anxiety, palpitations, increased heart rate, excessive sweating, feeling unusually hot, weight loss, irritability, difficulty sleeping. This phase is often mild and brief enough to be attributed to postnatal anxiety or general new-parent overwhelm.
Phase 2: Hypothyroid (roughly 4–8 months postpartum)
The thyroid hormone stores are depleted and the gland underproduces. Symptoms: profound fatigue, depression, weight gain, feeling cold, constipation, poor memory and concentration, hair loss. This is the phase most commonly misdiagnosed as postnatal depression or attributed to sleep deprivation.
After both phases, most women return to normal thyroid function. But around 20% remain permanently hypothyroid and require ongoing levothyroxine treatment — which is easily managed but requires the diagnosis to be made first.
The difficulty with postpartum thyroiditis is that its symptoms overlap with the normal experience of early parenthood so completely that both parents and clinicians frequently don't investigate further.
The symptoms that should prompt you to ask for a thyroid test — even if they feel like they could be explained by broken sleep and stress:
• Fatigue that feels disproportionate, or that isn't improving as the baby's sleep improves
• Mood symptoms (depression, anxiety, irritability) that are severe, persistent, or unresponsive to support
• Unexplained weight changes — either difficulty losing weight, or unexpected weight loss
• Feeling abnormally cold, or hot sweats
• Heart palpitations
• Significant hair loss (beyond the telogen effluvium expected at 3–6 months)
• Constipation that has appeared postnatal and isn't resolving
Any combination of these, especially if severe, is worth discussing with your GP.
Postpartum thyroiditis is diagnosed by a TSH (thyroid-stimulating hormone) blood test, taken at your GP surgery. It is a routine blood draw — no fasting required, results within a few days.
TSH measures how hard the pituitary gland is working to stimulate the thyroid. If the thyroid is overproducing (hyperthyroid), TSH is suppressed (low). If the thyroid is underproducing (hypothyroid), TSH is elevated (high). A free T4 test is often added to give the complete picture.
Ask specifically for a 'thyroid function test' or 'TFT' — and mention that you are postpartum and within the first year of delivery. If your GP suggests that your symptoms are explained by new parenthood and doesn't offer a test, you are entitled to ask for one specifically. The test costs the NHS very little and rules out a condition that, if present, is entirely treatable.
The hyperthyroid phase, if symptomatic, is managed with beta-blockers (such as propranolol) to control palpitations and anxiety. Antithyroid drugs are not used, because the thyrotoxicosis is from hormone release, not overproduction. The phase is usually self-limiting.
The hypothyroid phase, if symptomatic, is treated with levothyroxine — the synthetic thyroid hormone given as a daily tablet. This is one of the most commonly prescribed medications in the UK and has an excellent safety record, including in breastfeeding. It typically produces significant symptom improvement within 4–8 weeks.
Two things to know long-term: annual thyroid function tests are recommended after a PPT episode because of the elevated risk of permanent hypothyroidism developing over years. Your GP should know to arrange this; if they don't, ask. And if you have a future pregnancy, tell your GP and midwife early so monitoring can be arranged from the start.