Thyroid Disease in Pregnancy — Diagnosis, Treatment & Postpartum Care
Thyroid disease is common in pregnancy — hypothyroidism affects roughly 2–3% in western series and more in Indian studies; overt hyperthyroidism about 0.2–1%
Pregnancy changes thyroid tests: hCG lowers TSH in the first trimester, oestrogen raises TBG and total T4, and iodine needs rise
The fetus depends on maternal T4 until about 12 weeks and partly until term, so untreated disease affects pregnancy and neurodevelopment
Most problems are treatable: levothyroxine for hypothyroidism, antithyroid drugs for Graves disease, and no treatment for transient gestational thyrotoxicosis
Known thyroid disease, goitre, thyroid surgery, or symptoms
Positive TPO antibodies, or autoimmune disease (type 1 diabetes, vitiligo, coeliac)
Infertility, recurrent miscarriage, or preterm birth
BMI ≥ 40, previous head or neck radiation, family history
Amiodarone, lithium, or iodine-contrast use; living in an iodine-deficient area
India: the MoHFW guideline screens high-risk women at the first ANC visit; the Indian Thyroid Society favours universal TSH screening
TSH first, with free T4 if TSH is abnormal
Prefer free T4 by a reliable assay; total T4 needs a ×1.5 correction
Add TPO antibodies in subclinical hypothyroidism, recurrent loss, or infertility
TRAb (TSH receptor antibody) if Graves disease is suspected or known
Use the laboratory's trimester-specific range; otherwise TSH upper limit about 4.0 mIU/L
| TSH | Free T4 | Diagnosis | Action |
|---|---|---|---|
| High (above range) | Low | Overt hypothyroidism | Start levothyroxine; refer |
| ≥ 10 mIU/L | Any | Treat as overt | Start levothyroxine |
| High | Normal | Subclinical hypothyroidism | Treat if TPO-positive; consider if TPO-negative and TSH above about 4 (and treat when ≥ 10) |
| Normal | Low | Isolated hypothyroxinaemia | No treatment is advised; check iron and iodine; repeat later |
| Low or suppressed | High | Overt hyperthyroidism | Find the cause (Graves or gestational); refer |
| Low | Normal | Subclinical hyperthyroidism | No treatment; repeat in 4–6 weeks |
| Normal | Normal, TPO-positive | Euthyroid with antibodies | No routine treatment; check TSH every 4 weeks in the first half of pregnancy |
Targeted screening of high-risk pregnant women at the first antenatal visit, using serum TSH (venous sample, drawn with the other ANC tests in one sitting; chemiluminescence or auto-analyser)
High-risk groups: area with iodine insufficiency; BMI ≥ 30; past thyroid disease or surgery; goitre or symptoms; family history of thyroid disease or intellectual disability; autoimmune disease (type 1 diabetes, SLE, RA, Addison's, coeliac)
Obstetric and other triggers: recurrent miscarriage, preterm birth, IUD, pre-eclampsia or eclampsia, abruption; infertility; amiodarone, lithium, or recent iodinated contrast
Rollout: medical colleges first, then district hospitals, CHCs and PHCs; ASHA and ANM identify and counsel high-risk women and follow up those on treatment
| Trimester | Reference TSH (mIU/L) | Target on treatment |
|---|---|---|
| First | 0.1 – 2.5 | Below 2.5 |
| Second | 0.2 – 3.0 | Below 3.0 |
| Third | 0.3 – 3.0 | Below 3.0 |
| First TSH | Action under the national protocol |
|---|---|
| Below the upper limit (< 2.5 in the first trimester, < 3 later) | No treatment; routine care; repeat TSH 6 weeks after delivery |
| 2.5–10 (first trimester) or 3–10 (later) — subclinical | Levothyroxine 25 micrograms a day during pregnancy; stop after delivery |
| Above 10 in any trimester — overt | Levothyroxine 50 micrograms a day; continue the same dose after delivery |
| Already on levothyroxine | Continue and adjust to the same targets; return to the pre-pregnancy dose after delivery |
| Topic | What the guideline says |
|---|---|
| Repeat TSH | 4–6 weeks after starting or changing the dose, until the target is reached |
| Dose steps up (TSH above target) | 25 → 50 → 75 → 100 → 125 micrograms a day |
| Dose steps down (TSH below 0.1) | 100 → 75 → 50 → 25 → 12.5 micrograms; avoid over-treatment |
| How to take it | Morning, empty stomach, 30 minutes before food; if a day is missed, double the next dose |
| Supply | Levothyroxine 25, 50, 75 and 100 microgram strengths are budgeted for supply through the programme |
| Referral | Women with hypothyroidism and medical or obstetric complications go to a physician or obstetrician at a district hospital or medical college; uncomplicated women can deliver at PHC or CHC |
| Tracking | Follow up through MCTS / RCH portal; the ANM visits women on treatment to check adherence |
| Situation | What to do |
|---|---|
| Newly diagnosed overt hypothyroidism | Start about 1.6 micrograms/kg/day (often 75–100 micrograms); recheck TSH in 4 weeks |
| Already on levothyroxine | Increase the dose by 25–30% at once when pregnancy is confirmed (for example, take 2 extra tablets a week, making 9 per week) |
| Target | TSH in the lower half of the trimester range, or below about 2.5 mIU/L |
| Monitoring | TSH every 4 weeks until about 20 weeks, and at least once around 30 weeks |
| Taking the tablet | On an empty stomach; keep iron, calcium, and antacids 4 hours apart; take it again if she vomits soon after |
| After delivery | Return to the pre-pregnancy dose; check TSH at about 6 weeks |
| Subclinical, TPO-positive | Start 25–50 micrograms; titrate to target |
Mother: miscarriage, anaemia, pre-eclampsia, placental abruption, postpartum haemorrhage, and preterm birth
Baby: low birth weight, stillbirth, respiratory distress, and lower IQ and developmental delay in severe or untreated disease
TPO antibodies alone raise the risk of miscarriage and preterm birth; routine levothyroxine for euthyroid TPO-positive women is not advised, but regular TSH checks are
Congenital hypothyroidism screening (heel-prick TSH) is done in all newborns
| Feature | Gestational transient thyrotoxicosis | Graves disease |
|---|---|---|
| Cause | High hCG stimulates the TSH receptor | TSH-receptor stimulating antibodies |
| Timing | Weeks 8–14; settles by 14–18 weeks | Before or during pregnancy; may flare in the first trimester |
| Clues | Hyperemesis, twins, molar pregnancy; no goitre or eye signs | Goitre, eye disease, pretibial myxoedema, previous history |
| TRAb | Negative | Positive |
| Treatment | Supportive (fluids, antiemetics); no antithyroid drugs; beta-blocker if severe | Antithyroid drugs, beta-blocker for symptoms |
| Course | Resolves; ask about a molar pregnancy | Often improves in later pregnancy; postpartum relapse is common |
| Question | Advice |
|---|---|
| Which drug? | Propylthiouracil (PTU) in the first trimester (weeks 6–10 are the high-risk window for malformations); carbimazole or methimazole may be used later — avoid frequent switching |
| Why not methimazole early? | Aplasia cutis, choanal or oesophageal atresia, and other defects; PTU carries a smaller risk of face and neck defects and rare liver failure |
| How much? | Use the lowest dose that keeps free T4 at the upper end of normal; do not use block-and-replace |
| Monitoring | Free T4 and TSH every 2–4 weeks, then every 4–6 weeks once stable |
| Side effects | Agranulocytosis (sore throat, fever — stop and check counts); PTU hepatitis (check liver tests) |
| Symptom relief | Propranolol short term; avoid long use (growth restriction) |
| Surgery | Reserve for drug failure or allergy; best in the second trimester |
| Radioiodine | Contraindicated in pregnancy; avoid conception for about 6 months after treatment |
Maternal TRAb crosses the placenta and can cause fetal or neonatal thyrotoxicosis, even if the mother is euthyroid after surgery or radioiodine
Check TRAb at 20–24 weeks; if more than 3 times the upper limit, or the mother is on antithyroid drugs, arrange fetal ultrasound every 4 weeks
Watch for fetal heart rate above 170 bpm, goitre, growth restriction, hydrops, and advanced bone age
Tell the paediatrician before birth: the neonate needs observation for thyrotoxicosis in the first 1–2 weeks and a thyroid test; antithyroid drugs in the mother can also cause neonatal hypothyroidism
Total intake 250 micrograms a day in pregnancy and breastfeeding (WHO)
Use iodised salt (national standard 15 ppm iodine) and add a 150 microgram supplement as advised
Avoid excess (above about 500 micrograms a day), including kelp products
Remember that salt restriction in hypertension can reduce intake
Continue levothyroxine or antithyroid drugs through labour
Controlled Graves disease needs no change in the mode of delivery
Neonatal team informed if TRAb is high
Thyroid storm may follow infection, PPH, or surgery — look for early signs
Postpartum thyroiditis affects about 5–10% of women, and more with TPO antibodies or type 1 diabetes
Typical course: thyrotoxic phase at 1–4 months (painless, no antithyroid drug; propranolol if symptomatic), then hypothyroid phase at 4–8 months (levothyroxine if symptomatic)
Test TSH at 3 and 6 months if fatigue, palpitations, low mood, or weight change; many women return to normal, but about one in four has permanent hypothyroidism in later years
Differentiate from Graves relapse (TRAb positive, goitre, eye signs, raised uptake) and from postpartum depression, which can be caused by thyroid disease
Breastfeeding: levothyroxine is safe; carbimazole or methimazole up to about 20 mg a day and PTU are acceptable — take the dose just after a feed; radioiodine requires stopping breastfeeding
Thyroid nodules: ultrasound and FNAC are safe; avoid radioiodine scans; surgery for cancer can usually wait until after delivery
Using non-pregnant reference ranges and labelling normal first-trimester TSH as abnormal
Not increasing levothyroxine early — the requirement rises by weeks 4–6
Treating gestational thyrotoxicosis with antithyroid drugs, or treating isolated low free T4 with levothyroxine
Missing a Graves relapse or ignoring TRAb and fetal surveillance
Forgetting the postpartum dose reduction and the postpartum thyroiditis window
