Iron stores in pregnancy.

Serum ferritin concentration has been measured during the course of pregnancy in 154 women. There was a rapid decrease in iron stores during early pregnancy irrespective of any iron therapy. Oral iron did, however, prevent the stores reaching iron deficient levels during the second half of pregnancy. The results suggest that maternal erythroid activity starts early in pregnancy and may exhaust the iron stores before the fetal demands for iron can be met.