Abstract. Iron absorption, bone-marrow smears and haematological parameters were repeatedly studied during pregnancy in 50 women. The same studies were repeated two months after delivery. The material was randomly divided into two groups. Twenty-four women were treated with 200 mg of ferrous iron daily while 26 were given placebo. The iron absorption was measured from radioiron-labelled test doses of 100 mg ferrous iron in a whole-body counter with high sensitivity.

In the placebo group the iron absorption increased throughout pregnancy from an average of 6.5 % at the 12th week to 14.3 % at the 35th week of gestation. Two months after delivery the absorption was higher than initially. In the iron-treated group the absorption increased between the 24th and 35th week of gestation from 6.0 to 8.6 %. After delivery 5.5 % of the test dose was absorbed.

The haemosiderin iron in the bone-marrow was mobilized during pregnancy. In the placebo group no woman had more than trace of haemosiderin in the bone-marrow smears at the 35th week of gestation. In the iron-treated group 65 % had the same bone-marrow findings. The amount of bone-marrow haemosiderin at term seems not to have the same significance for the diagnosis of iron deficiency in pregnancy as in non-pregnant subjects. Two months after delivery about 50 % of the women in the placebo group had restored their iron depots. In the iron-group the haemosiderin content in the bone-marrow smears was enhanced in most women compared to early pregnancy. In the placebo group haematoLogical data indicated a high frequency of iron deficiency in late pregnancy while in the iron-treated group iron deficiency was prevented.