U-shaped curve for risk associated with maternal hemoglobin, iron status, or iron supplementation

Abstract

Both iron deficiency (ID) and excess can lead to impaired health status. There is substantial evidence of a U-shaped curve between the risk of adverse birth outcomes and maternal hemoglobin concentrations during pregnancy; however, it is unclear whether those relations are attributable to conditions of low and high iron status or to other mechanisms. We summarized current evidence from human studies regarding the association between birth outcomes and maternal hemoglobin concentrations or iron status. We also reviewed effects of iron supplementation on birth outcomes among women at low risk of ID and the potential mechanisms for adverse effects of high iron status during pregnancy. Overall, we confirmed a U-shaped curve for the risk of adverse birth outcomes with maternal hemoglobin concentrations, but the relations differ by trimester. For low hemoglobin concentrations, the link with adverse outcomes is more evident when hemoglobin concentrations are measured in early pregnancy. These relations generally became weaker or nonexistent when hemoglobin concentrations are measured in the second or third trimesters. Associations between high hemoglobin concentration and adverse birth outcomes are evident in all 3 trimesters but evidence is mixed. There is less evidence for the associations between maternal iron status and adverse birth outcomes. Most studies used serum ferritin (SF) concentrations as the indicator of iron status, which makes the interpretation of results challenging because SF concentrations increase in response to inflammation or infection. The effect of iron supplementation during pregnancy may depend on initial iron status. There are several mechanisms through which high iron status during pregnancy may have adverse effects on birth outcomes, including oxidative stress, increased blood viscosity, and impaired systemic response to inflammation and infection. Research is needed to understand the biological processes that underlie the U-shaped curves seen in observational studies. Reevaluation of cutoffs for hemoglobin concentrations and indicators of iron status during pregnancy is also needed.Am J Clin Nutr 2017;106(Suppl):1694S-702S.

Nutritional Anaemia and Obesity in the Eastern Mediterranean Region: The Protective Role of Breastfeeding for Two Years

“…The highest correlations were evident with LBW, stunting in CU5 and overweight in adults. These correlations were similar for pregnant and non-pregnant women substantiating the findings of other workers (14) who showed that anaemia affects pregnancy outcome depending on the prepregnant and early pregnancy state of anaemia and although it increases during pregnancy, its ultimate outcome is determined by its prepregnant state (14) .…”

“…Trend analysis revealed a U-shaped curve (14) which correlates with the high rates of LBW in EMR. Hence iron supplementation may improve LBW especially in LIC.…”

“…On the other hand excess iron during pregnancy may have adverse effects on birth outcomes, including oxidative stress, increased blood viscosity, and impaired systemic response to inflammation and infection (14) . High levels of hemoglobin, hematocrit, and ferritin are associated with an increased risk of fetal growth restriction, preterm delivery, and preeclampsia.…”

“…Breastfeeding supports iron absorption and uptake and can be protective against anaemia (14,15) . Other studies .…”

“…Some studies have shown that supplementation during pregnancy may not be necessary (13) and may increase the risk of LBW and on the contrary others suggest that supplementation is recommended (14) . Furthermore some workers suggest that breastfeeding is protective for infants (15,16) and for the breastfeeding mother by preserving and building her iron stores.…”