A woman normally experiences an increase in intravascular volume during pregnancy with hypervolemia. This is associated with a number of clinical and laboratory changes.
Clinical findings:
(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
Imaging findings:
(1) increased heart size with evidence of hypervolemia on chest X-ray
Laboratory findings:
(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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