A disease caused by determinants occurring in the antenatal period leading to changes in the concentration of red blood cells. This disease is characterised by having a high concentration of red blood cells in the body leading to slow flow of blood. This disease may present with headaches, blurred vision, red skin, tiredness, high blood pressure, dizziness, periods of confusion, bleeding problems, gout or itchy skin. Confirmation is by identification of increased levels of red blood cells in a blood sample.