Maternal adaptations to pregnancy: Renal and urinary tract physiology
- Ravi I Thadhani, MD, MPH
Ravi I Thadhani, MD, MPH
- Professor of Medicine
- Harvard Medical School
- Sharon E Maynard, MD
Sharon E Maynard, MD
- Associate Professor of Medicine
- Morsani College of Medicine
- University of South Florida
- Section Editors
- Richard J Glassock, MD, MACP
Richard J Glassock, MD, MACP
- Editor-in-Chief — Nephrology
- Section Editor — Glomerular Diseases
- Emeritus Professor
- The David Geffen School of Medicine at UCLA
- Richard H Sterns, MD
Richard H Sterns, MD
- Editor-in-Chief — Nephrology
- Section Editor — Fluid and Electrolytes
- Professor Emeritus
- University of Rochester School of Medicine and Dentistry
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.
URINARY TRACT CHANGES
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 . 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 . 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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- URINARY TRACT CHANGES
- Increased renal size
- Vesicoureteral reflux
- URINARY SYMPTOMS
- Frequency and nocturia
- Urgency and incontinence
- Postpartum changes
- RENAL HEMODYNAMICS
- Increase in GFR
- - Mechanisms
- Estimation of GFR
- OTHER CHANGES
- Mild hyponatremia
- Increased protein excretion
- Chronic respiratory alkalosis
- Decrease in serum anion gap
- Impaired tubular function
- POLYURIA AND DIABETES INSIPIDUS
- Transient DI of pregnancy
- - Management
- Subclinical central or nephrogenic DI
- Other causes of DI in pregnancy
- SUMMARY AND RECOMMENDATIONS