Respiratory and renal changes of normal pregnancy
Progesterone-driven hyperventilation and the compensated respiratory alkalosis of pregnancy, the fall in FRC with preserved spirometry, the 50% rise in GFR and what it does to creatinine, urea, glucose and protein handling, the reset osmostat, and why pregnancy ranges change how you read an ABG or a creatinine.
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
- Progesterone makes the respiratory centre more sensitive to CO2. Tidal volume rises and PaCO2 falls to about 30 mmHg; the kidney excretes bicarbonate to compensate.
- FRC falls about 20% as the uterus pushes the diaphragm up 4 cm, but airway calibre is unchanged, so spirometry and peak flow stay normal.
- GFR rises about 50% by the end of the first trimester. Creatinine, urea and urate fall, and glucose and protein spill more easily into urine.
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Sources
- SOMANZ Hypertension in Pregnancy Guideline 2023AU/NZSociety of Obstetric Medicine of Australia and New Zealand (NHMRC approved), 2023 (current; no later SOMANZ hypertension guideline found, November 2026)
- Summary of the 2023 Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) hypertension in pregnancy guidelineAU/NZShanmugalingam R et al. Med J Aust 2024, 2024
- The SOMANZ position statement on pulmonary embolism in pregnancy and post-partumAU/NZSociety of Obstetric Medicine of Australia and New Zealand (Lowe SA, Barrett HL, Cutts BA et al.), 2021
- de Swiet's Medical Disorders in Obstetric Practice (5th ed.)Wiley-Blackwell (Powrie, Greene and Camann, eds), 2010
- Physiological changes in pregnancy. Soma-Pillay P, Nelson-Piercy C, Tolppanen H, Mebazaa A. Cardiovasc J Afr 2016;27:89-94Cardiovascular Journal of Africa, 2016
- Powrie RO et al. Alveolar-arterial oxygen gradient in acute pulmonary embolism in pregnancy. Am J Obstet Gynecol 1998;178:394-396American Journal of Obstetrics and Gynecology, 1998
- Smith MC, Moran P, Ward MK, Davison JM. Assessment of glomerular filtration rate during pregnancy using the MDRD formula. BJOG 2008;115:109-112BJOG, 2008
- Wiles K, Bramham K, Seed PT et al. Serum creatinine in pregnancy: a systematic review. Kidney Int Rep 2019;4(3):408-19Kidney International Reports, 2019
- Last updated
- 14 November 2026
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