Haematological changes during normal pregnancy: iron induced macrocytosis.

Haematological indices in 300 pregnant and 50 non-pregnant women were obtained by Coulter Counter analysis. In 47 women who did not receive iron supplements during pregnancy, haemoglobin concentration fell from a mean of 12-23 g/dl in early pregnancy to 11-04 g/dl at 34 weeks gestation, a level which was maintained until term. In the 153 women to whom iron supplements were given during pregnancy, the initial fall in haemoglobin concentration was less, was arrested by 28 weeks gestation and then rose to a level equivalent to the booking level. This different pattern in iron supplemented pregnancies was due to an increase in the red cell count together with a change in mean cell volume. Although the changed mean cell volume usually remained within the normal range in the group who did not take iron, a few women developed microcytosis which could reflect iron deficiency; a macrocytic change was noted in a small number of the women who received routine iron supplements and this could reflect iron "over sufficiency". The results are discussed in relation to the possible effects of giving routine oral iron to all pregnant women.