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 (+/- SD: 32.9 +/- 1.4 wk gestation) oral 57Fe (10 mg) and intravenous 58Fe (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 57Fe 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 57Fe 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, 58Fe 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.