Thyroid disorders in pregnancy
Thyroid physiology in pregnancy, targeted TSH testing (ATA 2026 triggers) and laboratory-specific TSH ranges, levothyroxine dose increases, subclinical disease and TABLET, Graves versus gestational transient thyrotoxicosis, PTU and carbimazole timing, TRAb and fetal thyrotoxicosis, and postpartum thyroiditis.
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Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- hCG stimulates the TSH receptor, so TSH falls in the first trimester and free T4 rises slightly. Rising oestrogen doubles thyroxine-binding globulin, so total T4 and T3 rise by about 50%.
- The fetus relies on maternal T4 in the first half of pregnancy: its thyroid starts making hormone at about 12 weeks but doesn't function fully until about 18 to 20 weeks. Untreated overt hypothyroidism raises the risk of miscarriage, pre-eclampsia, preterm birth and impaired neurodevelopment.
- Testing is targeted, not universal (ATA 2026, RCOG 2025). Use laboratory-specific ranges; if none exist, the TSH upper limit is 4.0 mU/L (ATA since 2017).
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Sources
- American Thyroid Association 2026 guidelines for thyroid disease in preconception, pregnancy, and postpartumAmerican Thyroid Association (Korevaar, Leung, Alexander et al., Thyroid 2026;36(5):481-544), 2026 (replaces the 2017 ATA pregnancy guideline; key recommendations read via the 2026 editorial summary below, November 2026)
- Management of thyroid disorders in pregnancy (RCOG Green-top guideline)Chan SY, Marsh MS, Gilbert J et al., BJOG 2025;132(8):e130-61, 2025
- Navigating the RCOG 2025 and ATA 2026 guideline updates on the management of thyroid disorders during pregnancyAthanasiadou KI, Peppa M, Kalantaridou SN, Paschou SA. Case Rep Womens Health 2026, 2026 (editorial, open access)
- 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartumAlexander EK et al., Thyroid 2017;27:315-89, 2017 (superseded by ATA 2026; cited for the origin of the 4.0 mU/L fallback and lactation doses)
- Croce L et al. Graves' disease and the post-partum period: an intriguing relationship. Front Endocrinol 2019;10:853 (compares ATA 2011, ATA 2017 and ETA 2018 lactation doses)Frontiers in Endocrinology, 2019
- Therapeutic Guidelines: Endocrinology (thyroid disease in pregnancy and postpartum)AU/NZTherapeutic Guidelines Ltd
- Australian Pregnancy Care Guidelines (thyroid testing and iodine supplementation)AU/NZLiving Evidence for Australian Pregnancy and Postnatal Care, funded by the Australian Government Department of Health, Living guideline, 2024 onwards
- Levothyroxine in women with thyroid peroxidase antibodies before conception (TABLET)Dhillon-Smith RK et al., N Engl J Med 2019;380:1316-25, 2019
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Turnstile bot check on sign-in and signed-out feedback