Maternal Physiological Changes During Pregnancy, Labor, and the Postpartum Period

  • Sanjay Datta
  • Bhavani Shankar Kodali
  • Scott Segal


Maternal blood volume increases during pregnancy, and this involves an increase in plasma volume as well as in red cell and white cell volumes.1 The plasma volume increases by 40–50%, whereas the red cell volume increases by only 15–20%, which causes a “physiological anemia of pregnancy” (normal hemoglobin 12 g/dL; hematocrit 35).2 Because of this hemodilution, blood viscosity decreases by approximately 20%. The exact mechanism of this increase in plasma volume is unknown. However, several mediators such as renin–angiotensin–aldosterone, atrial natriuretic peptide, estrogen, progesterone, and nitric oxide may be involved. The most likely hypothesis attributes the increase to an “underfill” state caused by initial vasodilation, which stimulates hormones such as renin, angiotensin, and aldosterone to cause fluid retention.3 Alternatively, some have proposed an “overfill” state characterized by an early increase in sodium retention (due to an increase in mineralcorticoids) that leads to fluid retention, causing an increase in blood volume, followed subsequently by vasodilation.


Atrial Natriuretic Peptide Gravid Uterus Plasma Volume Increase Cardiac Output Increase Epidural Venous Plexus 
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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Sanjay Datta
    • 1
    • 2
  • Bhavani Shankar Kodali
    • 1
    • 2
  • Scott Segal
    • 1
    • 2
  1. 1.Brigham & Women’s HospitalBostonUSA
  2. 2.Harvard Medical SchoolBostonUSA

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