Maternal iron status influences iron transfer to the fetus during the third trimester of pregnancy

Background: The effect of maternal iron status on fetal iron deposition is uncertain. Objective: We used a unique stable-isotope technique to assess iron transfer to the fetus in relation to maternal iron status. Design: The study group comprised 41 Peruvian women. Of these women, 26 received daily prenatal supplements containing iron and folate (n = 11; Fe group) or iron, folate, and zinc (n = 15; Fe+Zn group) from week 10-24 of pregnancy to 1 mo postpartum. The remaining 15 women (control group) received iron supplementation only during the final month of pregnancy. During the third trimester of pregnancy ((x) over bar +/- SD: 32.9 +/- 1.4 wk gestation) oral Fe-57 (10 mg) and intravenous Fe-58 (0.6 mg) stable iron isotopes were administered to the women, and isotope enrichment and iron-status indicators were measured in cord blood at delivery. Results: The net amount of Fe-57 in the neonates' circulation (from maternal oral dosing) was significantly related to maternal iron absorption (P < 0.005) and inversely related to maternal iron status during the third trimester of pregnancy: serum ferritin (P < 0.0001), serum folate (P < 0.005), and serum transferrin receptors (P < 0.02). Significantly more Fe-57 was transferred to the neonates in non-iron-supplemented women: 0.112 +/- 0.031 compared with 0.078 +/- 0.042 mg in the control group (n = 15) and the Fe and Fe+Zn groups (n = 24), respectively (P < 0.01). In contrast, Fe-58 tracer in the neonates' circulation was not significantly related to maternal iron status. Conclusion: The transfer of dietary iron to the fetus is regulated in response to maternal iron status at the level of the gut.