Apart from low Hb, also elevated Hb levels are associated with adverse perinatal outcome.4,15–17 As a result of poor plasma expansion, blood viscosity increases, leading to a reduction in blood flow and fetomaternal exchange of oxygen and nutrients in the placenta.15,16 High Hb concentrations are associated with pregnancy-induced hypertension and preeclampsia.15–17. This evidence concerns the gene GSTM1 and hypertension, pregnancy-induced.