During pregnancy the intravascular volumes gradually increase, plateauing at the time of delivery. The volumes return to normal by 6 weeks postpartum.
Total blood volume:
(1) The blood volume tends to increase from 1,500 to 2,000 mL during the average pregnancy
(2) The actual increase is variable, with women having normal pregnancies showing increases of 20-100% of the nonpregnant volumes.
(3) Women with twin gestations have a slightly greater increase in blood volume.
Week of Gestation
112% of nonpregnant
Values are estimates from AABB Technical Manual (1993), graph on page 766, taken from Peck (1979) Figure 1 page 788.
The increase in plasma volume can be modeled by the equation of Smith and Yarborough (see 02.09.07, above).
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