Endocrine and metabolic changes of normal pregnancy: thyroid, glucose and calcium
How hCG and oestrogen change thyroid tests, why insulin resistance rises in the second half of pregnancy and what that means for gestational diabetes and DKA, the placental and renal drive to calcium absorption with falling total calcium, and the adrenal, pituitary and lipid changes that make non-pregnant reference ranges misleading.
Tier 1Medical sciences concept
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 and oestrogen doubles TBG, so first-trimester TSH falls and total T4 rises. Read free T4 against pregnancy ranges.
- Early pregnancy is anabolic: fasting glucose falls and the mother stores fat. From mid-pregnancy, placental hormones cause insulin resistance, and insulin secretion must rise two- to threefold. Gestational diabetes is the failure of that beta-cell response.
- Accelerated starvation and a low bicarbonate make pregnant women prone to ketosis and euglycaemic DKA.
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Sources
- Australasian Diabetes in Pregnancy Society (ADIPS) 2025 consensus recommendations for the screening, diagnosis and classification of gestational diabetesAU/NZSweeting A, Hare MJ, de Jersey SJ, et al. Med J Aust 2025;223(3):161-167, 2025 (replaces the 2014 ADIPS criteria)
- American Thyroid Association 2026 guidelines for thyroid disease in preconception, pregnancy, and postpartumAmerican Thyroid Association, Thyroid 2026, 2026 (replaces the 2017 ATA pregnancy guideline)
- 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
- Kovacs CS. Maternal mineral and bone metabolism during pregnancy, lactation, and post-weaning recovery. Physiol Rev 2016;96:449-547Physiological Reviews, 2016
- Hyperglycemia and adverse pregnancy outcomes (HAPO). N Engl J Med 2008;358:1991-2002New England Journal of Medicine, 2008
- de Swiet's Medical Disorders in Obstetric Practice (5th ed.)Wiley-Blackwell (Powrie, Greene and Camann, eds), 2010
- Last updated
- 14 November 2026
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