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
|
Blood Volume
|
Plasma Volume
|
RBC Volume
|
|
10
|
112% of nonpregnant
|
109%
|
103%
|
|
20
|
126%
|
120%
|
110%
|
|
30
|
133%
|
127%
|
114%
|
|
40
|
136%
|
130%
|
115%
|
|
at delivery
|
136%
|
131%
|
116%
|
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).
