Calcium
Calcium is primarily needed in pregnancy for fetal skeletal mineralization and maintenance of maternal bone health.
Approximately 30 grams of calcium (a little over an ounce) is transferred from the mother to the fetus during pregnancy. Fetal demand for calcium peaks in the third tri-mester when fetal bones are mineralizing at a high rate.163 Calcium metabolism changes meaningfully during pregnancy. Absorption of calcium from food increases, excretion of calcium in urine decreases, and bone mineral turnover takes place at a higher rate.164 The additional re-quirement for calcium in the last quarter of pregnancy is approximately 300 mg per day and may be obtained by in-creased absorption and by release of calcium from bone.165 (Calcium is not taken from the teeth, however.166) Calcium lost from bones appears to be replaced after pregnancy in women with adequate intakes of calcium and vitamin D.165 Inadequate calcium intake has been related to increased blood pressure during pregnancy, decreased subsequent bone remineralization, increased blood pressure of infants, and decreased breast-milk concentration of calcium.163
Calcium and the Release of Lead from Bones Lead in maternal blood can cross the placenta and be taken up by the fetus.168 Elevated blood lead levels in pregnancy are a cause for concern because they are related to miscarriage, preterm birth, low-birth-weight infants, impaired central nervous system development, and subsequent developmental delays in children.167 Poor, urban, and immigrant popula-tions are at greater risk for exposure to lead-based paint and environmental contamination than are other groups in the United States.169
Pregnant women who do not consume enough calcium show greater increases in blood lead levels than women who consume 1000 mg (the DRI for calcium) or more per day. Bone tissues contain about 95% of the body’s lead content, and the lead is released into the bloodstream when bones demineralize. Bone tissues de mineralize to a greater extent in pregnant women who fail to consume adequate calcium.167
Calcium needs during pregnancy can be met by drink-ing 3 cups of milk or calcium-fortified soymilk, or 2 cups of calcium-fortified orange juice plus a cup of milk, or by choosing a sufficient number of other good sources of calcium daily. (Table 1.14 in Chapter 1 lists food sources of calcium.)
Fluoride
Teeth begin to develop in utero, so why isn’t it recom-mended that pregnant women consume sufficient fluoride so that the fetus builds cavity-resistant teeth? A limited amount of fluoride is transferred from the mother’s blood to the developing enamel of the fetus. Major gains in the fluoride composition of enamel, however, occur in the Obese women appear to be at increased risk for
inadequate vitamin D status due to low levels of release of stored vitamin D from fat cells. As many as 61% of obese women have been identified as having low serum levels of vitamin D compared to approximately 36% in women who are not obese.161 Vegan women are at risk for poor vitamin D status because vitamin D is naturally present only in ani-mal products. Risk factors for inadequate vitamin D status
iron during the last two months in utero. Preterm infants are at risk for iron deficiency in infancy because they have less time to accumulate iron in late pregnancy.176
Assessment of Iron Status Red cell mass increases substantially (30%) in pregnancy. However, plasma vol-ume expands more (by about 50%). The higher increase in plasma volume compared to red cell mass makes it ap-pear that amounts of hemoglobin, ferritin, and packed red blood cells have decreased. They have not decreased but rather have become diluted by the large increase in plasma volume. Hemoglobin concentration normally decreases until the middle
of the second trimester and then rises somewhat in the third. It is not necessary to prevent normal declines in hemoglobin level during pregnancy.177
Due to the dilution ef-fects of increased plasma volume, changes in hemo-globin levels tend to be more indicative of plasma volume
expansion than of iron status.174 Low levels of hemoglobin or serum ferritin may be associated with high plasma vol-ume expansion (hyper volemia), and high hemoglobin levels are related to low plasma volume expansion (hypo-volemia). Low levels of plasma volume expansion are as-sociated with reduced fetal growth, whereas newborns tend to be larger in women with higher levels of plasma volume expansion.177
The Centers for Disease Control have developed standard hemoglobin levels to be used in the identifica-tion of iron-deficiency anemia in pregnant women. These standards (shown in Table 4.26) represent levels below the 5th percentile of hemoglobin values in pregnancy.178 years after birth when enamel in primary and permanent
teeth fully develops and hardens.170 Children of pregnant women given fluoride supplements during pregnancy have the same rates of dental caries as do children of women who did not receive supplements.171
Iron
Iron status is a leading topic of discussion in prenatal nu-trition because the need for iron increases substantially;
women require about 1000 mg (1 g) of additional iron for pregnancy.
300 mg is used by the fetus and placenta.
●
250 mg is lost at delivery.
●
450 mg is used to increase red blood cell mass.
●
Maternal iron stores get a boost after delivery when iron liberated during the breakdown of surplus red blood cells is recycled.172
Approximately 12% of women enter pregnancy with iron deficiency and little stored iron, and conse-quently are at risk of developing iron-deficiency anemia in pregnancy.173
Iron-Deficiency Anemia in Pregnancy Over recent decades, rates of iron-deficiency anemia in pregnancy have remained high in women in developing as well as developed countries (Table 4.25). Iron-deficiency anemia at the begin-ning of pregnancy increases the risk of preterm delivery and low-birth-weight infants by two to three times.174 Iron deficiency during pregnancy is related to lower scores on intelligence, language, gross motor, and attention tests in af-fected children at the age of 5 years.175 The mechanisms underlying these effects are unknown, but they may be re-lated to decreased oxygen delivery to the placenta and fe-tus, increased rates of infection, or adverse effects of iron deficiency on brain development.174 Iron deficiency often occurs toward the end of pregnancy even among women who enter pregnancy with some iron stores. It is far more common than iron-deficiency anemia.
Iron deficiency and iron-deficiency anemia are related to reduced iron stores in newborns. A fetus from a well-nourished mother is able to store a 6 to 8 month supply of
Iron Deficiency A condition marked by depleted iron stories. It is characterized by weakness, fatigue, short attention span, poor appetite, increased susceptibility to infection, and irritability.
Iron-Deficiency Anemia A condition often marked by low hemoglobin level it is characterized by the signs of iron deficiency plus paleness, exhaustion, and a rapid heart rate.
Table 4.25 Estimates of the incidence of iron-deficiency anemia in women in developing and developed countries172,173
% with Iron-Deficiency Anemia Developing
Countries
Developed Counties
Nonpregnant 43 12
Pregnant 56 18
Table 4.26 CDC’s gestational age-specific cutoffs for anemia in pregnancy178
Gestational Weeks
Hemoglobin (g/dL) Indicating Anemiaa
12 ,11.0
16 ,10.6
20 ,10.5
24 ,10.5
28 ,10.7
32 ,11.0
36 ,11.4
40 ,11.9
aFor women living in high altitudes, hemoglobin values should be increased by 0.2 g/dL for every 1000 feet above 3000 and by 0.3 g/dL for every 1000 feet above 7000. For cigarette smokers, hemoglobin values should be adjusted upward by 0.3 g/dL.
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associated with development of maternal postpartum depression.55
Pros and Cons of Iron Supplementation Absorption of iron from multimineral supplements is substantially lower than is iron absorption from supplements contain-ing iron only. For example, women given a multimineral supplement containing iron, calcium, and magnesium absorb less than 5% of the iron, whereas women given a similar dose of iron in a supplement containing iron only absorb over twice that much.239
The amount of iron absorbed from supplements de-pends primarily on women’s need for iron and the amount of iron in the supplement. As can be seen in Illustration 4.19, the amount of iron absorbed from supplements decreases substantially as the dose of iron increases. Acceptance of high levels of iron supplementation by women is often poor. Nausea, cramps, gas, and constipation are associated with the presence of free iron in the intestines, and these side effects increase as doses of supplemental iron increase (Table 4.27). Side effects experienced in using iron supple-ments are a major reason that women fail to take them.173 Unused iron supplements, when stored and later found by young children, pose a risk of iron poisoning. Difficulties related to building iron stores during pregnancy provide a strong rationale for screening women for iron status prior to pregnancy and establishing good levels of stored iron before pregnancy if needed.173
A relatively new concern about high-dose iron supple-ments is emerging. Iron supplesupple-ments providing 60 mg or more iron per day regularly expose the intestinal mucosa to free iron radicals. The oxidizing effects of iron radicals cause inflammation and mitochondrial damage in cells.242 In addition, iron doses over 30 mg per day may decrease zinc absorption status.34
By trimester, hemoglobin levels indicative of iron-deficiency anemia are:
● ,11.0 g/dL in the first and third trimesters
● ,10.5 g/dL in the second trimester
Serum ferritin cut-points indicative of iron-deficiency ane-mia in pregnancy have also been developed:178
Serum Ferritin, ng/mL
Normal .35
Depleted Stores ,20
Iron Deficiency #15
Hemoglobin and serum ferritin are the most commonly employed measures of iron status in pregnant women.178
The diagnosis of iron-deficiency anemia is more com-plicated than often thought. No single test of iron status is totally accurate because (1) many factors, including in-fection and inflammation, affect iron status; and (2) each test measures a different aspect of iron status. It is best to base the diagnosis of iron-deficiency anemia on results of several tests.178
Women entering pregnancy with adequate iron stores tend to absorb about 10% of total iron ingested; those with low stores absorb more—about 20% of the iron consumed.
The largest percentage of iron absorption, 40%, occurs in women who enter pregnancy with iron-deficiency anemia.
Iron absorption from foods and supplements is en-hanced in women with low iron stores during pregnancy, and absorption increases as pregnancy progresses.34 Absorption is highest after the thirtieth week of preg-nancy, when the greatest amount of iron transfer to the fetus occurs. Maternal iron depletion in preg-nancy decreases fetal iron stores, increases the risk that infants will develop iron- deficiency anemia, and is
30
20
10
40 35 30 25 20 Week of Gestation
15 10 5 00
Iron Absorption by Dose, %
18 mg
39 mg
120 mg
10
5
40 35 30 25 20 Week of Gestation
15 10 5 00
Iron Absorption by Dose, mg
18 mg 39 mg 120 mg
source: From Pedro Rosso, Nutrition and Metabolism in Pregnancy: Mother and Fetus. Copyright © 1990 by Oxford University Press, Inc. Used by permission of Oxford University Press, Inc.
Illustration 4.19 Effect of does of supplemental iron on iron absorption in women during pregnancy.
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Iodine
Iodine is required in pregnancy by the mother and fetus for thyroid function and energy production, and for fe-tal brain development.179 Deficiency of iodine early in pregnancy can lead to hypothyroidism in the offspring.
Hypothyroidism in infants is endemic in parts of southern and eastern Europe, Asia, Africa, and Latin America.180 The incidence of infant hypothyroidism has been found to decrease by over 70% when at-risk women in developing countries are given iodine supplements before or in the first half of pregnancy.
Rates of infant deaths are also substantially improved, as is the psychomotor development of the offspring.181 Iodine supplementation in the second half of pregnancy does not improve infant outcomes.180
About half of pregnant women in the United States consume less than the recommended 220 mcg of iodine daily, and 7% have low urinary iodine levels.182 The most reliable source of iodine is iodized salt. One teaspoon con-tains 400 mcg iodine. Fish, shellfish, seaweed, and some types of tea provide iodine. Women who consume iodized salt are not likely to need supplemental iodine.183 Kelp and seaweed should not be used as a source of iodine because they vary too much in iodine content.179 Iodine can also be provided through supplements containing iodine. The American Thyroid Association recommends that prenatal supplements contain 150 mcg of iodine.184 Usual iodine in-take should not exceed 1100 mcg daily during pregnancy.
Sodium
Sodium plays a critical role in maintaining the body’s water balance. Requirements for it increase mark-edly during pregnancy due to plasma volume expan-sion. But the need for increased amounts of sodium in pregnancy hasn’t always been appreciated. Thirty years ago in the United States, it was accepted practice to put all pregnant women on low-sodium diets. It was then thought that sodium increased water retention and blood pressure, and that sodium restriction would pre-vent edema and high blood pressure. We now know this isn’t accurate and that inadequate sodium intake can complicate the course and
outcome of pregnancy.184 Sodium restriction during pregnancy may exhaust so-dium conservation mecha-nisms and lead to excessive sodium loss.190
Sodium restriction is
not indicated in normal pregnancy or for the control of edema or high blood pressure that develops in pregnancy.
Women should be advised to consume salt “to taste” un-less contradicted by a medical condition related to salt intake. 191
Amounts of elemental iron in supplements vary depend-ing on the form of the iron compound in the supplement (Table 4.28). The proportion of iron absorbed from a constant amount of iron from each type of supplement listed in Table 4.28 is approximately equal.243
Recommendations Related to Iron Supplementa-tion in Pregnancy It is generally recommended that pregnant women in the United States take a 30-mg iron supplement daily after the twelveth week of pregnancy.244 Women with iron-deficiency anemia are often given 60–180 mg of iron per day.245
It has been suggested that women’s iron status be assessed at the first prenatal visit to determine if there is a need for iron supplements. A 30-mg iron supplement would be indicated when hemoglobin levels are ,11 g/dL, or if serum ferritin levels are ,30 ng/mL. Women with higher values would be monitored for iron status but not given a supplement.244
Recommended Intake of Iron During Preg-nancy The increased need for iron can be met by in-takes that lead to an additional 3.7 mg absorbed iron per day on average throughout pregnancy. This is a large increase, especially considering that nonpregnant women consuming the DRI for iron (18 mg) absorb only around 1.8 mg of iron daily. Given an ongoing need for 1.8 mg of absorbed iron a day, and the additional need of 3.7 mg of iron daily for pregnancy, the total need for absorbed iron during pregnancy is 5.5 mg daily. Assuming 20% of iron consumed is absorbed, average iron consumption of 27 mg per day (the RDA for iron for pregnancy) will meet the iron needs of pregnancy. The Upper Limit for iron in-take during pregnancy is set at 45 mg per day.
Table 4.27 Increased occurrence of side effects in women by supplemental iron dose240, 241 Dose of Iron, mg/day Side Effects
60 32%
120 40%
240 72%
Table 4.28 Percent of elemental iron by weight in various types of iron supplements
Supplement Type Iron Content
Ferrous sulfate 20%
Ferrous gluconate 12%
Ferrous fumarate 32%
Hypothyroidism A condition characterized by growth impairment and mental retardation and deafness when caused by inadequate maternal intake of iodine during pregnancy. Used to be called cretinism.
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although conclusions about caffeine’s effects on pregnancy are largely based on coffee intake, it is possible that other components of coffee are respon-sible for effects observed. Coffee is by far the largest contributor to caffeine intake in most people,193 and pregnant women consume on average 144 mg caffeine from coffee per day in pregnancy.194 (Table 2.5 in Chap-ter 2 provides a list of the caffeine content of beverages and foods.)
Despite the possibilities, evidence from well-controlled trials of caffeine or coffee intake and fetal growth restriction, malformations, preterm birth, and delivery complications does not support a relationship.195,196 No long-term consequences of coffee intake during pregnancy have been observed in children 7 years later. Children of women who drank coffee during pregnancy have been found to have similar levels of intellectual and neuromo-tor development when compared to children of non-coffee drinkers.196 Avoidance of caffeine and coffee during preg-nancy does not appear to improve pregpreg-nancy outcomes or infant birth weight.195 It is generally concluded that intake of up to 4 cups of coffee per day during pregnancy is safe.196