Table 1 Physiologic changes in various systems during pregnancy

Respiratory system

Increased alveolar ventilation (70%)

Relative hypocarbia (PaCO₂ of 25-32 mm Hg)

Reduced functional residual capacity (20%)

Increased O₂ consumption

Reduced venous oxygen saturation (SvO₂)

Cardiovascular system

Increased cardiac output (40%)

   Increased stroke volume 25%, increased heart rate 25%

Reduced total peripheral resistance

Normal CVP in superior vena cava distribution

Elevated CVP in inferior vena cava distribution

   Aorto-caval compression

Increased circulating volume

Increased plasma volume (40%-50%)

Increased red cell mass (20%)

   Physiologic anemia

Gastrointestinal and metabolic

Reduced lower esophageal sphincter tone

   Elevated risk of gastro-pulmonary aspiration

Increased metabolism

   Carbohydrate +++

   Protein ++

   Fat +

Hyperglycemia (due to insulin resistance)

Kidney

Increase renal blood and plasma flow (50%-60%)

Increased glomerular filtration (50%-60%)

Reduced serum urea and creatinine

Glycosuria

Mild proteinuria

Hematopoietic system

Reduced hemoglobin concentration (functional anemia despite elevated red cell mass)

Slightly elevated leucocyte count

Slightly reduced platelet count

Increased clotting tendency