Abstract
Objectives
It has been estimated that 90 mg of iron (Fe) is retained by a ∼600 g term placenta to support placental needs, but this value is based on limited data. While there has been an increase in studies evaluating placental Fe content (p[Fe]), there is also substantial variability in published values. Our aims were to characterize p[Fe] in pregnant women at risk of Fe deficiency and to identify determinants of p[Fe].
Methods
Placentae were collected at 39.8 ± 1.2 weeks of gestation from 132 neonates born to teens carrying singletons (≤18 y) and at 35.3 ± 2.4 weeks of gestation from 101 neonates born to 48 women carrying multiples (20–46 y). Maternal and cord blood samples were collected and maternal and neonatal Fe status indicators (hemoglobin, serum ferritin (SF), transferrin receptor (sTfR), serum Fe, total body Fe (TBI)) and regulatory hormones (erythropoietin (EPO), hepcidin) were measured. Inductively coupled plasma-mass spectrometry was used to measure p[Fe].
Results
Mean placental weight per fetus was 290 ± 74 g in the multiples and 619 ± 149 g in the teens (p < 0.001). Mean p[Fe] was 23 mg per placenta [95%CI 15–33] in the multiples and 40 mg per placenta [95%CI 31–51] in the teens (p = 0.03). Mean μg of Fe per g of placental wet tissue did not differ between the two cohorts. Maternal anemia had opposite effects on p[Fe] in the two cohorts. In women carrying multiples, mean μg of Fe per g of placenta was higher in anemic compared to non-anemic women (p = 0.02). In contrast, mean μg of Fe per g of placenta was lower in anemic compared to non-anemic teens (p = 0.04). These divergent observations were supported by observed associations between p[Fe] and maternal Fe status markers at delivery. In women carrying multiples, low maternal Fe status [lower SF (p = 0.002) and lower TBI (p = 0.01)] was associated with higher μg of Fe per g of placenta, while in teens, improved Fe status [lower sTfR (p = 0.03) and higher TBI (p = 0.03)] was associated with higher μg of Fe per g of placenta.
Conclusions
These human data show that p[Fe] is significantly associated with maternal Fe status but determinants of p[Fe] differ between adult women and teens who may still be growing. Using current methodology, the average p[Fe] was found to be ∼50% lower than previously estimated. More data are needed to characterize p[Fe] and understand maternal and neonatal determinants of p[Fe].
Funding Sources
The USDA and Gerber Foundation.