All of the following may be observed in a normal pregnancy EXCEPT:
Fall in serum iron concentration
Increase in serum iron binding capacity
Increase in blood viscosity
Increase in blood oxygen carrying capacity
Blood thins out in pregnancy due to the hemodilution of pregnancy. The increase in Blood volume (30-45%) is relatively greater than that of red cell mass (20-30%) resulting in hemodilution and a decrease in haemoglobin concentration. Fibrinogen as well as factors VII , IX, X and XII increase markedly. These changes tend to prevent excessive bleeding at delivery. Pregnancy is a hyper-coagulable state thus, but this is not synonymous with "Increased viscosity" .
Physiological Changes of Pregnancy