Maternal hemoglobin concentration and birth weight

Pregnancy requires additional maternal absorption of iron. Maternal iran st atus cannot be assessed simply from hemoglobin concentration because pregna ncy produces increases in plasma volume and the hemoglobin concentration de creases accordingly. This decrease is greatest in women with large babies o r multiple gestations. However, mean corpuscular volume does not change sub stantially during pregnancy and a hemoglobin concentration <95 g/L in assoc iation with a mean corpuscular volume <84 fL probably indicates iron defici ency. Severe anemia (hemoglobin <80 g/L) is associated with the birth of sm all babies (from both preterm labor and growth restriction), but so is fail ure of the plasma volume to expand. Hemoglobin concentrations >120 gn at th e end of the second trimester are associated with a less than or equal to 3 -fold increased risk of preeclampsia and intrauterine growth restriction. T he minimum incidence of low birth weight (<2.5 kg) and of preterm labor (<3 7 completed weeks) occurs in association with a hemoglobin concentration of 95-105 g/L. This is widely regarded as indicating anemia in the pregnant w oman but, if associated with a mean corpuscular volume >84 a, should be con sidered optimal.