Talk to your health care provider about an iron supplement. The National Academy of Sciences recommends that all pregnant women following a balanced diet take an iron supplement providing 27 mg of iron during the second and third trimesters of pregnancy (that's the amount in most prenatal vitamins). Your doctor may increase this dose if you become anemic. Iron deficiency anemia is a condition in which the size and number of red blood cells are reduced. This condition may result from inadequate intake of iron or from blood loss.