A woman normally experiences an increase in intravascular volume during pregnancy with hypervolemia. This is associated with a number of clinical and laboratory changes.
(1) increased cardiac output with decrease in systemic vascular resistance
(2) increased heart rate
(3) systolic flow murmur
(4) dependent ankle edema
(5) increased body weight
(1) increased heart size with evidence of hypervolemia on chest X-ray
(1) decrease in hemoglobin and hematocrit (nadir at 32-33 weeks)
(2) limited change in serum BUN, with the serum BUN to creatinine ratio < 15
(3) normal creatinine clearance
The absence of these findings may indicate relative hypovolemia which may indicate a problem with the pregnancy, including pre-eclampsia. Oligohydramnios may be a manifestation of maternal hypovolemia
The plasma volume can be measured directly if there is a question about hypovolemia.
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