Should Pregnant Women Be Screened or Routinely Supplemented to Prevent Iron Deficiency Anemia?
Pregnant women are at high risk of iron deficiency anemia, and the US Preventive Services Taskforce (USPSTF) recently updated their guidelines regarding screening for iron deficiency, or its prevention with routine supplementation. Pregnancy increases the demand for iron as both the fetus and the mother’s circulatory system require the production of iron-containing red blood cells. For this reason, guidelines for iron intake are much higher than for women who are not pregnant: women of childbearing age are recommended to consume at least 18 mg iron per day, and in pregnancy, recommendations increase to 27 mg per day.
Despite these optimistic recommendations, most women fail to meet even the 18 mg target: the Micronutrient Calculator shows that average daily iron consumption in the US for women aged 19 to 50 is only 13.3 mg per day, and 87% consume less than 18 mg per day. I would expect that virtually no one consumes 27 mg per day. This is because it is very difficult to meet these recommendations using food alone. Looking at two diet plans that meet a pregnant woman’s requirements, one from a website for endurance athletes (Pamela Morris Fitness), and another from the Vegetarian Resource Group, high-iron diets require daily consumption of fortified cereal for breakfast, legumes such as lentils, soybeans and chickpeas, large quantities of green leafy vegetables, and for non-vegetarians, high-iron meats especially some shellfish and organ meats for lunch and dinner, and snacking on high-iron foods like dried fruits and nuts. Foods like bread and eggs also make a modest contribution to iron intakes. Few people consume this type of diet.
If it is so difficult to meet iron recommendations though diet alone, why don’t we see higher rates of anemia? First of all, many pregnant women take a dietary supplement that contains iron and the amount of iron in the supplement is more than enough to meet dietary requirements. Branum, Bailey and Singer found that 73% of pregnant women use a dietary supplement containing iron, and the average iron content of the supplements was 48 mg, more than enough to meet requirements. Secondly, the absorption of iron from plant sources is highly variable and depends on various factors including the iron status of individuals. When iron stores are low, the body is able to increase absorption of iron (see review by Hurrell and Egli). Even though we can assume that iron intake from the diet is inadequate, the use of supplements, and the ability of the body to increase iron absorption, mean that rates of iron deficiency anemia are not as high as may be expected.
The USPSTF found that there is inconsistent evidence on the benefits and harms of anemia screening and routine iron supplementation in US women who do not have symptoms of iron deficiency anemia nor other factors that place them at risk of iron deficiency. Although iron supplementation during pregnancy improves iron status in pregnant women, a resulting improvement in health outcomes for mothers and newborns in the well-nourished US population has not been shown. In addition, women who are most at risk of iron deficiency, such as women who are food insecure (Park and Eicher-Miller), may not have the means to be tested for iron deficiency or purchase iron supplements. The effects of routine iron screening and supplementation in the US population needs further data to enable the development of useful recommendations.
Siu AL, on behalf of the U.S. Preventive Services Task Force. Screening for Iron Deficiency Anemia and Iron Supplementation in Pregnant Women to Improve Maternal Health and Birth Outcomes: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2015;163:529-536. doi:10.7326/M15-1707
Amy M. Branum, Regan Bailey, and Barbara J. Singer. Dietary Supplement Use and Folate Status during Pregnancy in the United States. J Nutr. 2013 143: 4 486-492; first published online January 30, 2013. doi:10.3945/jn.112.169987
Haider BA, Olofin I, Wang M, Spiegelman D, Ezzati M, Fawzi WW; Nutrition Impact Model Study Group (anaemia). Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis. BMJ. 2013 Jun 21;346:f3443. doi: 10.1136/bmj.f3443.
Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010 May;91(5):1461S-1467S. doi: 10.3945/ajcn.2010.28674F. Epub 2010 Mar 3.
Park CY, Eicher-Miller HA. Iron deficiency is associated with food insecurity in pregnant females in the United States: National Health and Nutrition Examination Survey 1999-2010. J Acad Nutr Diet. 2014 Dec;114(12):1967-73. doi: 10.1016/j.jand.2014.04.025. Epub 2014 Jun 20.