Blood volume adjustments in the normal obstetric patient with particular reference to the third trimester of pregnancy

1.1. There is an increase in response to pregnancy of total blood volume of the order of 30 per cent, plasma volume of the order of 40 per cent, and red cell volume of the order of 18 per cent.2.2. There is a significant individual variability in regard to the increase in whole blood volume and the proportionate increase in plasma and red cell volumes.3.3. The major response to the effect of pregnancy has occurred by the thirty-third week of pregnancy.4.4. The plasma volume remains unchanged with a small but significant increase in red cell volume during the last trimester on the basis of the mean levels of the present study.5.5. There is a significant individual variability of plasma and red cell volume adjustment during the last trimester within this general pattern with three distinct patterns observed in the present study.