GSTM1 and anemia (phenotype): Hence the plasma volume expansion increase exceeds the rise in RBC volume, resulting in haemodilution and consequent physiological anaemia of pregnancy,[9–14] with an average Hb and haematocrit of 11.6 gm/dL and 35.5%, respectively.[21] This represents a 15% decrease from prepregnancy levels.[9] The decrease in blood viscosity from the lower haematocrit reduces resistance to blood flow, as a compensatory mechanism.[10] However, if the Hb concentration falls < 10 gm/dL, other causes of anaemia should be considered.[9]