Author(s): Beard JL
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Abstract 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. PIP: Precise determination of indicators that have considerable within-subject variability is needed to assess iron deficiency in pregnant women. Within-subject day-to-day variation of serum ferritin levels may fluctuate as much as 25\%. The uncertainty of biological variability is accompanied by the uncertainty of concentration-dependent indexes (e.g., ferritin, plasma iron, and hemoglobin) caused by plasma volume expansion. Physicians should take several measurements to determine iron status in pregnant women. If they cannot do this, they should incorporate confidence limits around measurements of women assigned to iron-sufficient or iron-deficient groups. In central Pennsylvania, health workers determined the iron status of 88 pregnant adolescents attending the prenatal clinic at Altoona Hospital or the Allegheny Family Physicians Group in Altoona to examine within-subject variability of iron status and the prevalence of iron deficiency in this group. At entry into the pilot study, about 70\% of the pregnant teenagers had depleted iron stores. Even though the women were prescribed an iron supplement, depleted iron stores continued throughout pregnancy. Iron deficiency anemia was found in 7.4\% at the end of the 1st trimester of pregnancy. Another 3.6\% had anemia but not iron deficiency. At 2 weeks postpartum, 55\% had iron deficiency anemia. About 20\% had anemia with no signs of iron deficiency. When the researchers considered daily variability, the prevalence of depleted iron stores rose to 80\% from 69\%. All low birth weight infants (born to 8\% of subjects) were born to mothers who were iron deficient at 11-16 weeks of pregnancy. There is considerable doubt about an absolute diagnosis of iron status during pregnancy.
This article was published in Am J Clin Nutr
and referenced in Journal of Blood Disorders & Transfusion