Early hemodynamic changes include generalized vasodilation, some increase in the plasma volume, and an increase in red blood cell 2,3-diphosphoglycerate concentrations 3 , 4. There is also some evidence that erythropoietic activity may be reduced during this period, with a slight reduction in red blood cell mass 5 , a reduction in the number of reticulocytes 4 , and a rise in the serum ferritin concentration 4 , 6.
During the second trimester, iron requirements begin to increase and continue to do so throughout the remainder of pregnancy. The increase in oxygen consumption by both mother and fetus is associated with major hematologic changes. There has been some difficulty in establishing the normal hemoglobin concentration in pregnancy because of both the disproportionate increases in the plasma volume and the frequent occurrence of iron deficiency anemia.
Whereas this represents a significant drain during the later part of the pregnancy, it does not affect long-term iron balance because the iron is returned to the body's stores at the end of pregnancy, when the red blood cell volume gradually reverts to normal. As pregnancy progresses, iron requirements for fetal growth rise steadily in proportion to the weight of the fetus, with most of the iron accumulating during the third trimester 10; Figure 1. Relation between body weight and body iron content in the fetus and newborn child In determining iron requirements during pregnancy, the losses incurred during parturition must also be added.
These include an average maternal blood loss equivalent to mg Fe and a further 90 mg present in the placenta and umbilical cord 7. The net cost, however, is only mg because the iron used to increase the red blood cell mass is returned to stores and overall losses are further offset by the absence of menstruation during pregnancy. When total iron requirements during pregnancy are translated into increased daily needs, it is apparent that there is an unequal distribution over time Figure 2.
Although reduced during the first trimester, iron requirements rise to between 4 and 6 mg in the second and third trimesters, respectively Irrespective of the exact value, it is apparent that daily iron requirements cannot be met from dietary absorption alone in the latter part of pregnancy, even from the most optimal diet 7. The amount of iron absorbed is much lower when the diet contains only small amounts of bioavailable iron 4 , 12 , as is often the case in many developing countries where the staple food is cereal and the intake of meat and ascorbic acid is limited.
Estimated daily iron requirements during pregnancy in a kg woman. Modified from Bothwell et al 7 with permission. From the preceding discussion, it is apparent that iron balance can be maintained in pregnancy only when there are adequate iron stores at the start of pregnancy. If a woman routinely eats a diet high in bioavailable iron, a prepregnancy iron store of mg is probably sufficient to carry her through pregnancy, although a higher amount of stored iron is needed when the diet is less than optimal.
The extent to which women of reproductive age can meet their iron requirements during pregnancy has been estimated from studies that calculated iron stores through measurements of serum ferritin concentrations and other hematologic indexes, with use of the equation developed by Cook et al Although data do not exist to enable similar calculations for women in developing countries, the high prevalence of low serum ferritin concentrations and overt iron deficiency anemia in these populations indicate that a large proportion of the women enter pregnancy with little or no iron stores Studies with radioactive and stable isotope of iron have provided insights into the changes that occur in iron absorption during pregnancy.
The studies can be divided into those in which the absorption of nonheme iron from different mixed diets was measured and those in which the absorption of various doses of inorganic iron was measured.
The amount of iron absorbed in each of the studies differed because of variations in the iron dose and regimen. Nevertheless, the overall pattern was remarkably similar, with a progressive rise in iron absorption as pregnancy advanced. There is, however, some evidence that iron absorption decreases during early pregnancy, probably because of lower iron requirements.
In women who were to undergo legal abortion and who were fed a test meal in early pregnancy, iron absorption was only 2. In another study, the median iron absorption from a mixed meal was only 0. The relatively low values for iron absorption were ascribed to the meal's containing several iron absorption inhibitors. At the same time, the contribution of heme iron to overall iron absorption was not measured.
In this context, it is noteworthy that the median amount of nonheme iron absorbed during early pregnancy was 3 times greater when a highly iron-bioavailable hamburger meal was eaten Through the use of values for iron absorption during each trimester of pregnancy, total iron absorption heme and nonheme from a highly bioavailable diet containing adequate amounts of meat and ascorbic acid was calculated to be 0. Proportionately smaller amounts of iron would be absorbed from diets with a lower bioavailability, which is the case for most pregnant women in developing countries.
Further insights into the patterns of iron absorption in pregnancy and the effects that might be anticipated from using different doses of supplemental iron were obtained from studies in which ferrous iron was administered. In fasting subjects fed a small dose of ferrous iron 0. The absorption rates for a 5-mg dose of iron were lower: 7. Increasing the dose of ferrous iron to mg lowered the absorption rates even further to 6. The main conclusions that can be drawn from the above studies are that iron absorption decreases during the first trimester of pregnancy, rises during the second, and continues to increase throughout the remainder of pregnancy.
Iron absorption remains elevated during the first months after delivery, which allows for some reconstitution of body iron stores. Assessing iron status during pregnancy is fraught with difficulties because the profound hemodynamic changes associated with pregnancy affect several indexes of iron status.
During pregnancy, hemodilution leads to a reduced hemoglobin concentration, whereas both serum iron and ferritin concentrations decrease and total iron-binding capacity increases 8 , 22 , The relative contributions of pregnancy per se and a pregnancy-induced negative iron balance in bringing about these changes can be assessed by measuring the changes in hemoglobin, serum iron, serum ferritin, and total iron-binding capacity that occur during pregnancy in women rendered iron replete after adequate iron supplementation during pregnancy 8 , 22 , There is a moderate drop in the concentration of serum iron that stabilizes in the middle of pregnancy As a result, there is a drop in transferrin saturation.
As discussed previously, there is some evidence that serum ferritin rises modestly early in pregnancy, presumably because of reduced erythropoietic activity; thus, iron is diverted to stores 4 , 6. These changes reflect hemodilution and the mobilization of iron from stores to meet the increased demands of pregnancy.
Effects of iron supplementation on serum ferritin concentration in pregnancy. It is, therefore, apparent that all the indexes associated with iron deficiency—including hemoglobin, transferrin saturation, and serum ferritin concentrations—are reduced during pregnancy even in iron-replete women. In contrast, the concentrations of circulating transferrin receptor have been found to be normal in pregnancy, only being raised if iron deficiency is present 25 , This suggests that serum transferrin receptor concentrations may prove to be a useful tool for diagnosing iron deficiency in pregnancy.
Iron supplementation regimens in pregnancy vary depending on the characteristics of the population. In developed countries most women enter pregnancy with normal hemoglobin concentrations and variable amounts of stored iron.
In contrast, large numbers of women in developing countries are anemic at the onset of pregnancy In the World Health Organization WHO recommended universal supplementation of all pregnant women with 60 mg ferrous iron twice daily in populations where gestational anemia is common and once daily in populations where overall iron nutrition is better This recommendation was subsequently modified to a single daily dose of 60 mg Fe for 6 mo in pregnancy or mg Fe if 6 mo duration cannot be achieved Keeping the dose as low as is compatible with unimpaired effectiveness is an important principle because the side effects of iron therapy, which can seriously limit compliance, are dose-dependent phenomena Recommendations on the use of prenatal iron supplements need to be considered against the background of what is known about iron requirements and iron balance at the different stages of pregnancy.
The iron requirement during pregnancy is, as discussed previously, between and mg depending on the size of the woman 45—55 kg , with most of the extra requirements occurring in the second half of pregnancy. As was also discussed previously, iron absorption from a diet of very high iron bioavailability has been estimated to be 0. A diet with the above absorption rates would provide a total of mg Fe during pregnancy, leaving a deficit of — mg Fe that would have to be met by mobilizing iron from stores, if they exist, and from the absorption of supplemental iron.
The latter can probably be ascribed to both the consumption of a diet with relatively low iron bioavailability and poor compliance in taking iron supplements. Whether a dose larger than 30 mg of supplemental iron would reduce the prevalence of anemia is not clear, but note that in their classic study, de Leeuw et al 8 found that the mean hemoglobin mass at term was lower in women receiving 39 mg ferrous iron daily than in those receiving double that amount.
The problem of anemia during pregnancy in many developing countries is compounded by the fact that many women consume diets of low iron bioavailability and, therefore, enter pregnancy with no iron stores and less than optimal hemoglobin concentrations. In such circumstances, the iron deficit that must be met is correspondingly greater.
During the latter part of pregnancy, between and mg Fe can be absorbed from diets with low to medium bioavailability; thus, a deficit of as much as — mg must be met from iron supplementation. The extra amounts of iron that would have to be absorbed to meet such a deficit would be 5. The above absorption ranges are not out of line with those obtained in radioiron studies using a mg dose of ferrous iron 9.
For optimal results, the iron must be administered between meals because food reduces the absorption of iron substantially From the above calculations, it is apparent that a daily dose of 60 mg ferrous iron given to fasting pregnant women throughout the second half of pregnancy should be sufficient to combat iron deficiency in developing countries. However, a recent meta-analysis of the results from controlled studies raised questions about the optimal dose of iron supplementation.
These unexpected findings need to be confirmed because they appear to be at variance with the known relations between the dose of iron and the percentage absorbed 7 , 8 , Although virtually all well-controlled iron supplementation trials have shown a positive effect on status, in proportion to the dose and duration of iron therapy, there is little evidence that the results of such trials can be reproduced in national health care programs 34 , The latter is due to both biological and programmatic factors.
From the biological perspective, the etiology of anemia in developing countries is multifactorial and can be expected to vary by region and by season In addition to the poor bioavailability of dietary iron, intestinal worm infections and particularly blood loss from hookworm infections compound the problem of anemia in many areas Other important etiologic factors include folate deficiency 38 ; vitamin A deficiency 39 ; a variety of infections, including malaria and HIV infection 40 ; and hemoglobinopathies 36 , HIV infection is particularly prevalent in sub-Saharan Africa and has been shown to be associated with a median hemoglobin decrease of 5.
Programmatically, several factors can limit the effectiveness of iron supplement interventions, including problems related to costs and logistics that affect the supply of iron tablets, poor access to prenatal care, insufficient counseling on the need for and benefits of iron supplementation, and an unwillingness by pregnant women to take iron supplements Available literature from several countries suggests that the most important reason for the failure of supplementation programs is a lack of supplies 41 , but noncompliance on the part of pregnant women can also be a significant factor Noncompliance is the result of both an aversion to the side effects of taking iron supplements and the failure of many primary health care systems to adequately motivate both health care providers to issue the iron tablets and pregnant women to take them The problem of noncompliance was highlighted in 2 studies.
Various strategies have been adopted to reduce the gastrointestinal side effects associated with taking iron supplements, such as nausea and epigastric pain, which are important factors in noncompliance. So, almost all pregnant women need iron supplements for the rest of their pregnancy starting at weeks.
Hospital Foundation Research Education. Learn more about iron deficiency by clicking on the drop-downs below. What are the symptoms of iron deficiency? Iron deficiency makes it harder to exercise and concentrate, and causes tiredness. One in four pregnant women have iron deficiency. Some women are at higher risk of developing iron deficiency, including women: with heavy periods who eat vegetarian or vegan diets who donate blood regularly who have been pregnant many times who have a gluten sensitivity.
Pregnant women should aim to get 27 mg of iron from food each day. Only 4 mg of this is absorbed by the digestive system. Most pregnant women get less than 15 mg a day from food. To meet the target of 27 mg per day would require major changes to the average diet of women.
Iron supplements are recommended for pregnant women, as well as an iron-rich diet. Foods with heme iron Food mg of iron per 75 gram serving Liver pregnant women should avoid liver as it is too high in vitamin A 4.
Foods with non-heme iron Food mg of iron per serving Pumpkin seeds, kernels 60 mL 8. In This Article. Continue Reading Below. More Healthy Eating Tips. View Sources. August Rachel Fine, R. Tarun Jain, M. National Institutes of Health, U.
Your Health. Pregnancy Groups. Jump to Your Week of Pregnancy. Pregnancy Week. There's little risk of getting too much iron during pregnancy, especially if your levels were already low, so just follow your doctor's advice regarding supplements.
You may have heard upping your iron can cause constipation, and that's true, even if you are just raising your consumption to pregnancy-appropriate levels. Iron is binding so it can cause you to become backed up—and because constipation is already a common symptom during pregnancy , the combination isn't exactly a picnic.
In addition to taking a supplement, upping how much iron you're getting in your diet will also make a difference. Not all iron-containing foods are created equal, however. There are two types of iron: heme and non-heme. Non-heme iron is mostly found in beans, vegetables, dried fruits, eggs, whole grains, and iron-fortified products; heme iron comes from animal sources, such as red meat, fish, and poultry.
She recommends downing two servings of red meat per week during pregnancy. Mom-of-one Marisa Weigand, 31, in Port Washington, New York, kept this in mind when her iron levels were low during her pregnancy. Interestingly, what you consume with your iron can affect how well your body absorbs the mineral. Whether taking an iron supplement or eating iron-rich foods, downing them with calcium-containing items such as milk or cheese can actually reduce your body's ability to absorb it.
So you may want to rethink popping your supplement with your bowl of cereal.
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