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Maternal adaptations to pregnancy: Renal and urinary tract physiology

Ravi I Thadhani, MD, MPH
Sharon E Maynard, MD
Section Editors
Richard J Glassock, MD, MACP
Richard H Sterns, MD
Deputy Editor
Kristen Eckler, MD, FACOG


Normal pregnancy is characterized by profound changes in almost every organ system in order to accommodate the demands of the fetoplacental unit. This topic will review changes in the lower urinary tract and kidney.


Pregnancy affects both the kidney and the remainder of the urinary tract.

Increased renal size — Both kidneys increase in size by 1 to 1.5 cm during pregnancy [1]. Kidney volume increases by up to 30 percent, primarily due to an increase in renal vascular and interstitial volume. There are no histological changes or changes in number of nephrons, but the glomerular filtration rate is also increased (see 'Increase in GFR' below).

The renal pelvises and caliceal systems may be dilated as a result of progesterone effects and mechanical compression of the ureters at the pelvic brim (see 'Ureters' below).

Ureters — Dilatation of the ureters and renal pelvis (hydroureter and hydronephrosis) is more prominent on the right than the left and is seen in up to 80 percent of pregnant women [2]. These changes can be visualized on ultrasound examination by the second trimester, and may not resolve until 6 to 12 weeks postpartum.

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Literature review current through: Oct 2017. | This topic last updated: Aug 21, 2017.
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