Iron

Iron is an essential mineral necessary for transport of oxygen, as well as the production of hemoglobin and enzymes involved in many body functions. Physiologic iron requirements are 3 times greater in pregnant than in menstruating women.26 The increased need for iron in pregnancy is related to the growing placenta and fetus, and the expansion of blood volume by 50% increases demands for iron from 1.0 mg/dL at conception to 5.0 mg/dL by the second and third trimesters.27,28 The US Centers for Disease Control and Prevention defines anemia in pregnancy as hemoglobin concentration <11.0 g/dL in the first and third trimesters and <10.5 g/dL in the second trimester. An estimated 38% of pregnant women worldwide are anemic; in the United States, nearly 18% of pregnant women are anemic.28,29

In addition to the risk for anemia due to increased demand in pregnancy, the most common cause of iron deficiency is malnutrition, notably in those living in poverty or those consuming vegan or iron-poor diets. Other contributors include gastrointestinal absorption deficiencies and chronic blood loss.30

Iron supply in food comes in 2 forms: heme and nonheme. Heme iron is highly bioavailable (15%-35%) and is found primarily in animal foods, including chicken liver, oysters, clams, beef liver, beef, tuna, eggs, shrimp, and lamb.26 Nonheme iron is found in nonanimal food and in iron-fortified foods, and has low bioavailability (2%-20%). Nonheme iron foods include bran, instant oatmeal, beans, molasses, spinach, brown rice, and peanut butter.

Symptoms of iron deficiency are often attributed to symptoms of pregnancy; however, iron deficiency may be the source of some of these symptoms, including fatigue, tachycardia, lightheaded and dizzy feelings, shortness of breath, and restless legs.31 In pregnancy, symptoms of anemia are also associated with preterm labor, low birthweight, and newborn and maternal mortality.30

Recommendation: Adequate but not too much is the goal with iron; the upper limit of iron intake is 45 mg/d.32 Women of childbearing age benefit from supplementation of 18 mg/d of iron, with adjustments based on dietary habits and menstrual losses. Pregnant women may require 30 to 40 mg to meet metabolic iron requirements.33 Although iron obtained via dietary intake is not likely to meet the demand of pregnant women, a diet that is iron abundant and highly bioavailable is recommended. Ascorbic acid may support the absorption of iron; foods that inhibit iron absorption include milk, coffee, and black tea. Iron supplementation at bedtime or between meals may also enhance its absorption.34

Because primary care providers lay the foundation of health for future pregnancies, their guidance in preparing women for healthy pregnancies is essential. A large part of this includes understanding the potential effects of micronutrients on pregnancy outcomes. Women of childbearing age may benefit from some supplementation. Discussion with women regarding their plans for pregnancy, diet, and lifestyle will help practitioners determine how to best direct patients in their decision to supplement with micronutrients.

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Jodi Westfall, FNP-C, DCNP, PMH-NP-C, is an integrative medicine and nutrition specialist, and Jennifer Rode, PhD, ANP-C, is an associate professor in the Department of Nursing at Miami University in Hamilton, Ohio.

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