The physiological macrocytosis of pregnancy.

Sixty-four healthy women were followed during normal pregnancies in which they took supplements of iron or iron+folate or an inactive placebo. The red cell size increased in those patients receiving iron alone or iron+folate. The group on the inactive placebo who received no supplemental iron had red cells of constant size and a falling serum iron. Nineteen women not included in the trial developed macrocytosis during pregnancy:marrow samples from these showed normoblastic erythropoiesis in 18 and minor megaloblastic changes in one. Macrocytosis developing during pregnancy is a physiological change in the majority of cases.