Pathophysiology

During pregnancy the following hematological changes take place which contribute to a reduced Hb level:

Serum transferrin & Fe binding capacity  increases with an additional Iron demand of 1000mg which creates an Iron deficiency.

Increase in plasma volume, Plasma volume raises by 30–50% which is equivalent to 1200–1300 mls. In multigravidas it goes as high as 70%. Increased blood volume is necessary for adequate flow of blood into the uterus for fetal growth and to counter act blood loss later during delivery .

RBC production (under the influence of erythropoietin) increases by 18-25%. This disproportional increase in hematocrit and plasma, makes blood lighter than usual, hence Hemodilution or dilutional anemia occurs.