Iron Absorption and Partitioning During Pregnancy (OR35-03-19)

Iron (Fe) homeostasis must be tightly regulated during pregnancy to supply sufficient Fe to both the mother and her developing fetus. Stable isotopes have been utilized to understand Fe absorption during pregnancy by measuring maternal red blood cell incorporation. This measure, however, underestimates the true amount of Fe absorbed, as dietary Fe is transferred to the fetus and may be retained by the placenta. The objective of this study was to obtain a more accurate estimation of Fe absorption during pregnancy and determine factors associated with Fe partitioning between the mom, baby and placenta. Sixty-eight women (6 carrying multiple fetuses (age 27–33), 20 carrying singletons from Rochester NY (age 16–32), and 42 carrying singletons from Peru (age 18–30)) were dosed with an oral stable Fe isotope during late pregnancy. Iron absorption was calculated as the sum of tracer recovered in maternal and umbilical cord red blood cells (RBC) and for isotope retained in placental tissue. The net amount of Fe in each compartment was calculated based on Hb concentration, body (or placental) weight and estimated blood volume. Hemoglobin (Hb), serum ferritin (SF), soluble transferrin receptor (sTfR), folate and vitamin B-12 were assessed in maternal and cord blood. The amount of maternally absorbed Fe was significantly greater when neonatal and placental uptake of tracer was accounted for (Table 1). While the majority (> 85%) of absorbed Fe tracer was utilized by the mother for RBC production, neglecting net Fe tracer transferred to the placenta and neonatal compartment underestimated true Fe absorption by 4%-20%. There was a significant positive association between the net amounts of Fe tracer recovered in the fetal compartment and the maternal compartment (R2 = 0.63, P < 0.001). Net Fe tracer retained in placental tissue was significantly positively associated with the net amount of Fe tracer present in the neonatal RBC pool at birth (P = 0.04). Iron absorption was underestimated by up to 20% when absorbed Fe that was transferred to the fetus or retained by the placenta was not measured. More research on determinants of iron partitioning in pregnant women is needed to fully evaluate maternal Fe demands and absorption. National Institutes of Health, United States Department of Agriculture, Nestle Foundation.