Abstract: Maternal hematological system happens to have a series of physiological changes such as plasma volume expansion and hemodilution to adapt to the growth of the fetus during normal pregnancy. In contrast, high maternal hemoglobin concentrations usually coincide with hemo concentration and over activation of blood coagulation both of which alter blood rheology and result in adverse outcome of pregnancy such as hypertensive disorders in pregnancy,small for gestational age,premature birth,low birth weight gestational diabetes mellitus, still birth and so on. We summarize the effects of high maternal hemoglobin concentrations during gestation on the adverse pregnancy outcomes.

Key words: Hemoglobins, Pregnancy outcome, Hypertensive disorders in pregnancy, Gestational diabetes mellitus, Premature birth