Iron Deficiency and Iron Deficiency Anemia: Implications and Impact In
Total Page:16
File Type:pdf, Size:1020Kb
nutrients Review Iron Deficiency and Iron Deficiency Anemia: Implications and Impact in Pregnancy, Fetal Development, and Early Childhood Parameters Robert T. Means 1,2 1 Departments of Internal Medicine, Medical Education, and Pathology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA; [email protected]; Tel.: +1-423-439-6499; Fax: +1-423-439-6470 2 Internal Medicine, Building 2/Room 109, Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA Received: 26 December 2019; Accepted: 6 February 2020; Published: 11 February 2020 Abstract: A normal pregnancy consumes 500–800 mg of iron from the mother. Premenopausal women have a high incidence of marginal iron stores or iron deficiency (ID), with or without anemia, particularly in the less developed world. Although pregnancy is associated with a “physiologic” anemia largely related to maternal volume expansion; it is paradoxically associated with an increase in erythrocyte production and erythrocyte mass/kg. ID is a limiting factor for this erythrocyte mass expansion and can contribute to adverse pregnancy outcomes. This review summarizes erythrocyte and iron balance observed in pregnancy; its implications and impact on mother and child; and provides an overview of approaches to the recognition of ID in pregnancy and its management, including clinically relevant questions for further investigation. Keywords: iron deficiency; pregnancy; iron deficiency anemia; laboratory testing; iron supplementation; iron balance 1. Introduction Anemia with a hemoglobin (Hb) concentration no lower than 10 g/dL at term, occurs in nearly all pregnancies, and in the majority of cases reflects a physiologic process (discussed below) rather than a deficiency state or underlying hematologic disorder [1]. Significant anemia in pregnancy (defined as a Hb concentration <11 g/dL in the first trimester or <10 g/dL in the second and third trimesters) occurs with a prevalence ranging between 2% and 26%, depending upon the population studied [2–4]. Anemia is a major contributor to maternal and fetal morbidity and mortality, particularly in less developed countries [2–6]. Of the pathologic causes of anemia in pregnancy, anemia due to iron deficiency (IDA) is the most common, particularly in more developed countries, where contributions from other anemia-producing disorders such as malaria or hemoglobinopathies are less significant [7–9]. Anemia in pregnancy, and particularly IDA, is both a long-standing scholarly interest and an element of my practice as a hematologist. In preparing for this review, PubMed searches using the terms “pregnancy” and “iron deficiency” were performed. A date range was not specified, but the focus was on papers 2015 and later. Specific searches for subtopics included “hepcidin”, and “guidelines”. Approximately 71 reports, reviews, or studies new to the author were identified through this process. 2. Physiologic Anemia of Pregnancy The effects of ID on red cell production occur in the context of what is usually called the physiologic anemia of pregnancy. This is a phenomenon that is conserved across mammalian species [10,11], and it Nutrients 2020, 12, 447; doi:10.3390/nu12020447 www.mdpi.com/journal/nutrients Nutrients 2020, 12, 447 2 of 16 2. Physiologic Anemia of Pregnancy The effects of ID on red cell production occur in the context of what is usually called the physiologic anemia of pregnancy. This is a phenomenon that is conserved across mammalian species [10,11], and it is hypothesized that the physiologic anemia of pregnancy serves the purpose of enhancing placental perfusion by reducing maternal blood viscosity and facilitating oxygen and nutrient delivery to the fetus by expanding the erythrocyte mass [12]. Beginning approximately the sixth week of pregnancy, the plasma volume increases disproportionately to the erythrocyte mass, Nutrientsreaching2020 a, 12maximum, 447 value at approximately 24 weeks’ gestation. At maximum, the plasma volume2 of 15 is 40%–50% higher than at the start of pregnancy [13]. Since the parameters used to identify anemia in clinical practice (the hematocrit (Hct), the blood isHb hypothesized concentration, that and the physiologicthe circulating anemia erythrocyte of pregnancy count) serves are expressed the purpose as concentrations of enhancing placental based on perfusionwhole blood by reducing volume, maternal the expanded blood viscosityplasma volume and facilitating causes them oxygen to decrease and nutrient and deliveryhence produces to the fetus“anemia”. by expanding While Hb the concentration, erythrocyte mass Hct, [12 and]. Beginning to a lesser approximately degree erythrocyte the sixth count, week are of pregnancy,the anemia theindicators plasma volume used in increases practice, disproportionatelythese parameters are to the only erythrocyte surrogates mass, for the reaching actual adefinition maximum of value anemia: at approximatelya reduction in 24erythrocyte weeks’ gestation. mass per At unit maximum, body weight the plasma [14]. By volume this criterion, is 40–50% the higherphysiologic than anemia at the startof pregnancy of pregnancy is not [13 actually]. anemia: a 15%–25% increase in the erythrocyte mass occurs in pregnancy butSince is concealed the parameters by the dilutional used to identify effect of anemia the increase in clinical in plasma practice volume (the hematocrit [15]. This (Hct), is driven the blood by an Hbincrease concentration, in serum anderythropoietin the circulating concentrations erythrocyte during count) the are late expressed second and as concentrations early third trimesters based on[16] wholeand bloodis facilitated volume, or the potentially expanded plasmalimited volumeby iron causes availability. them to decreasePregnant andwomen hence using produces iron “anemia”.supplementation While Hb have concentration, a greater increase Hct, and in er toythrocyte a lesser degreemass than erythrocyte women not count, using are supplemental the anemia indicatorsiron [1], and used women in practice, with compromised these parameters iron are stores only at surrogates outset of pregnancy for the actual will definition have a limited of anemia: increase a reductionin erythrocyte in erythrocyte mass. The mass upper per limit unit of body erythrocyte weight [ 14mass]. By increase this criterion, in the presence the physiologic of adequate anemia iron of is, pregnancyhowever, isregulated not actually through anemia: erythropoietin a 15–25% increase control in and the is erythrocyte not raised mass by increased occurs in iron pregnancy availability: but ispregnant concealed women by the dilutional in the Bantu effect tribe, of the who increase have in plasmaboth an volume iron-rich [15 ].traditional This is driven diet by and an increasea genetic inpredisposition serum erythropoietin to increased concentrations dietary iron during absorption the late, do second not increase and early Hb third concentration trimesters [or16 Hct] and with is facilitatedsupplementation or potentially [17,18]. limited by iron availability. Pregnant women using iron supplementation have aAs greater a result increase of the in reset erythrocyte balance mass between than womenplasma notvolume using and supplemental erythrocyte iron mass, [1], it and is generally women withconsidered compromised that a Hb iron concentration stores at outset <11 of g/dL pregnancy in the la willte first have trimester a limited and increase <10 g/dL in erythrocyte in the second mass. and Thethird upper trimesters limit of should erythrocyte be investigated mass increase for a in cause the presence other than of adequatethe physiologic iron is, anemia however, of regulatedpregnancy through[19]. Figure erythropoietin 1 shows hemoglobin control and concentrations is not raised by by increased trimester iron based availability: on reports pregnant from Norway women [19], in theJamaica Bantu [20], tribe, and who China have [21]. both an iron-rich traditional diet and a genetic predisposition to increased dietaryMaternal iron absorption, plasma dovolume not increase generally Hb concentrationdecreases during or Hct the with final supplementation weeks of pregnancy, [17,18]. and consequentlyAs a result the of theHct, reset Hb, balance and circulating between plasmaerythrocyte volume count and increase erythrocyte [13]. mass,The maternal it is generally blood consideredvolume generally that a Hb returns concentration to prepregnancy<11 g/dL levels in the wi latethin first one trimester to six weeks and < after10 g/ dLdelivery in the and second maternal and thirderythropoiesis trimesters should increases be investigatedlate in gestation for a causeand re otherturns than to normal the physiologic by about anemia one month of pregnancy after delivery [19]. Figure[22]. 1 shows hemoglobin concentrations by trimester based on reports from Norway [ 19], Jamaica [20], and China [21]. Figure 1. Hemoglobin concentrations of healthy women during pregnancy (mean standard deviation. ± DataFigure combined 1. Hemoglobin from references concentrations [19–21]. of healthy women during pregnancy (mean ± standard deviation. Data combined from references [19–21]. Maternal plasma volume generally decreases during the final weeks of pregnancy, and consequently the Hct, Hb, and circulating erythrocyte count increase [13]. The maternal blood volume generally returns to prepregnancy levels within one to six weeks after delivery and maternal erythropoiesis increases late in gestation and returns to normal by about one month