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Web-Based Curriculum & Reference  
Editors
Kurt J. Pfeifer, MD, FACP
Steven L. Cohn, MD, FACP
 
Medical College of Wisconsin
State University of New York - Downstate
 
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  Pregnancy
Michael P. Carson, MD & David A. Halle, MD
 
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  Physiologic Changes of Pregnancy
 

Several changes in cardiovascular and pulmonary physiology occur during normal pregnancy (see table on right).

In addition, pregnant patients experience important changes in renal physiology:

  • Glomerular filtration rate (GFR) increases by 150% over the non-pregnant level.
  • 24-hour urine protein excretion increases to up to 300 mg (150 mg is normal in non-pregnant women).

Hepatic blood flow and metabolism do not change in pregnancy, but protein production, including albumin & coagulation factors, increases. However, lower levels of albumin and protein are normal due to dilution by the increased plasma volume.

Normal values of many laboratory studies are also significantly different in pregnancy (click here for table).


 
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CARDIOVASCULAR PHYSIOLOGY CHANGES

  • Systolic BP ↓ 10-20 mm Hg (nadir @ 20 weeks).
  • Diastolic BP ↓ 10 mm Hg (nadir @ 20 weeks).
  • HR ↑ 10%.
  • Plasma volume increases & peaks @ 28-32 weeks.
  • Cardiac output & stroke volume ↑ 50%, peaking @ 16 weeks.
  • HR measured when seated can be lower than when lying on the left side, especially if the BMI is >30. [3]
PULMONARY PHYSIOLOGY CHANGES
  • Diaphragm rises & anterior-posterior dimension increases.
  • Minute ventilation increases due to progesterone-mediated 50% ↑ in tidal volume - not an increase in respiratory rate.
  • Functional residual capacity (FRC) ↓ 70% when supine.
DRUG METABOLISM CHANGES
  • Increased GFR leads to increased clearance of many renally excreted medications.
  • Hepatic metabolism OF DRUGS IS NOT ALTERED
 
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