Iron deficiency: assessment during pregnancy and its importance in pregnant adolescents.

The assessment of iron deficiency in pregnancy requires the accurate determination of indicators that have significant within-subject variability. For instance, serum ferritin concentrations may vary by as much as 25% from one day to the next. Added to this uncertainty about biological variability is the influence of plasma volume expansion on concentration-dependent indexes such as ferritin, plasma iron, and hemoglobin. Multiple measurements of iron status are suggested, and, if this is not possible, within-subject variability needs to be included in the confidence of assigning individuals to iron-status groups. An example of this former approach is shown for a group of pregnant adolescents with a very high prevalence of iron deficiency. Although the assessment of iron status in human populations is advanced compared with that of other nutrients, there is still a large uncertainty about absolute diagnosis during pregnancy.