How would you manage a patient with erythrocytosis of unknown cause in pregnancy?

Pregnancy invokes changes in the blood volume and erythropoiesis: the plasma volume expands, erythropoietin production falls, and the hematocrit (don't use the hemoglobin level) declines (the hydremia of pregnancy) until the last trimester. So that by the third trimester, the hematocrit varies betwe...