Pediatric Annals

Nutrition During Teenage Pregnancy

Yolanda Gutierrez, MS, RD; Janet C King, PhD, RD

Abstract

Teenage pregnancy is one of the major public health problems in the United States. Based on data from the National Center for Health Statistics, the birth rate of 15- to 17-year-old girls jumped 10% between 1986 and 1988 to 33.8 births per 1000 girls. In all, 322 000 babies, about one twelfth of the 3.9 million babies born in 1988, were bom to teenagers. Nutrition is one of the most important environmental factors affecting the future health of the mother and her baby. Poor dietary habits are common among adolescents. Therefore, teens should receive dietary guidance early and throughout their pregnancies. Provision of dietary guidance to this population is a special challenge, however, that requires an understanding of the developmental issues of adolescents and the use of counseling approaches geared to teens.

This article reviews new information about nutritional needs during pregnancy. The National Academy of Sciences' Institute of Medicine published two reports within the past 3 years that make new recommendations for prenatal nutrition. The first was the latest edition of the Recommended Dietary Allowances issued in 1989.1 The recommendations for a number of vitamins and minerals were lowered in that report, and the need for energy during pregnancy was reassessed. The second report, released in 1990, made new recommendations regarding gestational weight gain and prenatal vitamin-mineral supplementation.2 The recommendations of these two reports are examined in this article with special consideration for the unique needs of adolescents.

LINEAR GROWTH BY ADOLESCENTS DURING PREGNANCY

The nutritional needs of adolescents will differ from that of mature women if the young girls are still experiencing physical growth. The physical growth spurt, as reflected by an increase in height, may start as early as 10 years of age or as late as 14 years, with an average onset of approximately 12½ years.3 Similar variability is noted in the onset of changes in weight-gain velocity. The average peak weight gain occurs at about 12½ years of age with a range from 10½ to 14½ years. The onset of menarche tends to occur toward the end of the spurt in linear growth. Onset of menarche at an early age is associated with greater rates of physical growth for longer periods of time postmenarche. Having gone through menarche does not necessarily mean that the young woman is fertile. The early menstrual cycles frequently are irregular and anovular, or infertile. Full fertility is not attained until some time, about 2 years, after the onset of menarche.3 At this time, growth will have slowed down considerably, but it is still occurring. For example, the 6-month weight change in a group of girls 2 years postmenarche was 1 kg (2⅕ lb), whereas it was 2.3 kg (5 lb) in the immediate 6 months after menarche.3

Table

Other Vitamins. Surveys of the nutrient intake of pregnant adolescents often show that intakes of vitamin D and E are below the amount recommended. Routine supplementation of these two vitamins is not recommended, however. In most regions of the United States, vitamin D status is maintained by good exposure to sunlight. Reported intakes of vitamin E range from 30% to 90% of the recommended intake. These estimates of intake may be low, however, because the dietary supply of vitamin E is difficult to assess. Food composition data are poor, and reported intake of fat and oil, the major sources of vitamin E in the diet, may be underestimated. Biochemical or clinical signs of low intakes of vitamins D and E among pregnant women in the United States are reported infrequently.

Minerals

The intake of three minerals, zinc, calcium, and iron, by pregnant…

Teenage pregnancy is one of the major public health problems in the United States. Based on data from the National Center for Health Statistics, the birth rate of 15- to 17-year-old girls jumped 10% between 1986 and 1988 to 33.8 births per 1000 girls. In all, 322 000 babies, about one twelfth of the 3.9 million babies born in 1988, were bom to teenagers. Nutrition is one of the most important environmental factors affecting the future health of the mother and her baby. Poor dietary habits are common among adolescents. Therefore, teens should receive dietary guidance early and throughout their pregnancies. Provision of dietary guidance to this population is a special challenge, however, that requires an understanding of the developmental issues of adolescents and the use of counseling approaches geared to teens.

This article reviews new information about nutritional needs during pregnancy. The National Academy of Sciences' Institute of Medicine published two reports within the past 3 years that make new recommendations for prenatal nutrition. The first was the latest edition of the Recommended Dietary Allowances issued in 1989.1 The recommendations for a number of vitamins and minerals were lowered in that report, and the need for energy during pregnancy was reassessed. The second report, released in 1990, made new recommendations regarding gestational weight gain and prenatal vitamin-mineral supplementation.2 The recommendations of these two reports are examined in this article with special consideration for the unique needs of adolescents.

LINEAR GROWTH BY ADOLESCENTS DURING PREGNANCY

The nutritional needs of adolescents will differ from that of mature women if the young girls are still experiencing physical growth. The physical growth spurt, as reflected by an increase in height, may start as early as 10 years of age or as late as 14 years, with an average onset of approximately 12½ years.3 Similar variability is noted in the onset of changes in weight-gain velocity. The average peak weight gain occurs at about 12½ years of age with a range from 10½ to 14½ years. The onset of menarche tends to occur toward the end of the spurt in linear growth. Onset of menarche at an early age is associated with greater rates of physical growth for longer periods of time postmenarche. Having gone through menarche does not necessarily mean that the young woman is fertile. The early menstrual cycles frequently are irregular and anovular, or infertile. Full fertility is not attained until some time, about 2 years, after the onset of menarche.3 At this time, growth will have slowed down considerably, but it is still occurring. For example, the 6-month weight change in a group of girls 2 years postmenarche was 1 kg (2⅕ lb), whereas it was 2.3 kg (5 lb) in the immediate 6 months after menarche.3

Table

TABLE 1Gestational Weight-Gain Recommendations for Adolescents *†

TABLE 1

Gestational Weight-Gain Recommendations for Adolescents *†

Pregnant adolescents appear to continue to grow, but the rate is slower than that observed in nonpregnant adolescents who are in the same stage of development.4 Also, the rate of linear growth, as measured by changes in leg length, is greater in very young teens (<15 years of age) than that observed in older girls (>15 years). This is to be expected because the normal rate of growth of girls older than 15 years of age is only about half that of girls who have just gone through menarche.3 In a study of more than 400 Peruvian adolescent mothers, the girls were classified as either still growing if they were shorter than their parents or growth completed if they were the same height or taller than their parents. Infants born to the mothers classified as still growing weighed significantly less at birth than those born to girls who had completed their growth, although maternal body size was similar for both groups.5

Fetal growth may be retarded in very young mothers who are still growing, theoretically because there is competition for a limited supply of nutrients between the adolescent mother and her fetus or because the immature mother has a reduced capacity to deliver nutrients to her fetus. The presence of fetal growth retardation among wellnourished, immature mothers would suggest that nutrient transfer to the fetus is limited. Studies of uteroplacental blood flow among very young pregnant teens who are not consuming limited diets are needed to confirm this hypothesis.

GESTATIONAL WEIGHT GAIN AND PREGNANCY OUTCOME

The effect of maternal age on gestational weight gain is unclear because most studies have failed to control for other factors known to influence weight gain, ie, parity, prepregnancy weight for height, gestational length, ethnicity, or alcohol and tobacco use. It is particularly important to control for parity since primiparous women of all ages tend to gain about 1 kg (2 lb) more than multiparous women.2 After controlling for parity, differences in weight gain as the result of age are small. The exception may be among very young adolescents (<2 years postmenarche) who tend to have lower weight gains than do other women.2 In a study of Peruvian pregnant adolescents, the gestational weight gain of those girls between 14 and 17 years of age did not differ, but the 12- and 13-year-old girls gained about 0.8 kg (1⅘ lb) less than the older girls did.6 Meserole and coworkers7 also found that pregnant adolescents of young gynecologic age gained less weight than did more mature girls. Further research on the weight gains of very young pregnant adolescents is needed.

Gestational weight gain is one of several factors contributing to pregnancy outcome in both young and mature women, but this effect is modified by the mother's prepregnancy weight for height2 or body mass index (BMI). Body mass index is the weight of the mother divided by the height squared; metric units of kilograms for weight and meters for height are used in the calculation.

Women who are thinner before pregnancy tend to have babies that are smaller than those of their heavier counterparts with the same gestational weight gain. There is little evidence that age modifies the effect of weight gain on fetal growth after controlling for other factors that influence pregnancy outcome (ie, prepregnancy weight for height, parity, and socioeconomic status). Only the very young adolescent (<2 years postmenarche) may be at risk of delivering smaller infants for a given weight gain than older women. The recommended2 ranges for weight gain for women with different prepregnant weights for height are presented in Table 1. The range reflects the wide variation in weight gain among women giving birth to live, optimally grown (ie, 3 to 4 kg at 39 to 41 weeks gestation) infants. Since the very young girl who is less than 15 years old is at higher risk of giving birth to a growth-retarded infant, she should gain weight in the upper end of the ranges.

Although the rate of weight gain varies widely from woman to woman, the average rates of gain across studies tend to be similar.2 During the second trimester, gains average about 0.45 kg (1 lb) per week and are slightly lower during the third trimester, about 0.40 kg (just under 1 lb) per week. Rates are lower in the first trimester, and there is less agreement across studies during early pregnancy.

Table

TABLE 2Recommended Energy Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 2

Recommended Energy Intakes for Nonpregnant and Pregnant Adolescents*

Among adolescents, early inadequate weight gain may reflect a risk of poor pregnancy outcome. In a cohort study of 1790 teenage gravidas from Camden, New Jersey,8 a weight gain of less than 4.3 kg by 24 weeks gestation was associated with a significantly increased risk of having a small-for-gestational-age infant, even when later gains brought the cumulative total gain up to recommended standards. Also, a low rate of gain, less than 0.4 kg/wk in late pregnancy from 24 weeks gestation to term, was associated with preterm delivery in this same group of pregnant teens.8 It is important, therefore, to monitor the rate of gain throughout gestation and to intervene if an abnormal pattern is identified. In particular, gains of less than 0.5 kg (1 lb) per month for obese girls and less than 1 kg (2 lb) per month for teens of normal weight for height require further evaluation. Gains greater than 3 kg (6½ lb) per month, especially after the 20th week of gestation, also should be evaluated. High rates of weight gain should never be viewed as a reason to limit food intake.

Accumulation of fluid is one possible reason for deviation from the normal pattern of weight gain. Garn et al4 suggested that pregnant adolescents disproportionately retain fluids during pregnancy. Early inadequate weight gains among teens may appear sufficient later in gestation if fluid retention occurs. A smooth, progressive change in weight represents a gain of lean and fat tissue, whereas erratic, high weight changes reflect fluid retention.2 Plotting maternal weight at each visit on a chart in the obstetrical record is a good method for detecting erratic changes in weight and, possibly, fluid retention.

The composition of the weight gained by pregnant teens is not known. The weight gain of adults, on average, is 62% water, 30% fat, and 8% protein.9 Rapid loss of weight in the early postpartum period would suggest that a high proportion of the gain is water. Studies of postpartum weight changes or measurements of changes in body composition have not been done in pregnant adolescents.

NUTRITIONAL REQUIREMENTS OF PREGNANT ADOLESCENTS

The nutritional requirements of pregnant teenagers are extrapolated from studies of adults. In practice, the needs of pregnant adults are added to the estimated requirements of nonpregnant adolescents. This practice assumes that the nutritional requirements for pregnancy is not influenced by age. As mentioned above, this assumption may not be true for very young adolescents who may still be growing or who may have a reduced capacity to transfer nutrients to the fetus. Consequently, in making nutritional recommendations for pregnant adolescents under 15 years of age, it is prudent to add a safety factor that may improve support for fetal growth.

Energy

The energy cost for a full-term pregnancy in which the mother gains 12.5 kg (27½ lb) and delivers a 3.3 kg (7⅓ lb) baby is estimated to be 80 000 total kcal or 300 kcal/day.1 Energy demands are thought to be the greatest between 10 and 30 weeks gestation, when relatively large quantities of maternal fat are deposited. Unless the adolescent enters pregnancy underweight, it is unnecessary to alter energy intake in the first trimester. Thus, the additional intake of 300 kcal/day is recommended for the second and third trimesters. Very young adolescents, who may still be growing, should consume an additional 200 kcal/day to bring their total increment to 500 kcal/day3 (Table 2).

Surveys of energy intake by pregnant women fail to show incremental increases comparable to the amount recommended. This has led to the conclusion that the increased energy needs for pregnancy are met, at least in part, by reductions in physical activity.9 Overestimation of the energy cost of pregnancy is an alternative explanation. When the energy content of tissue deposited plus the metabolic cost for maintaining that tissue are actually measured, the values are lower than the theoretical estimate of 80 000 kcal. For example, the energy cost of pregnancy among women in Scotland and Holland totaled 67 000 and 60 720 kcal, respectively; the needs of women in Thailand and the Philippines were lower, 49 620 and 43 210 kcal, respectively.10 Women in Gambia subsisting on marginal diets required only 18 680 kcal. From these data, it has been suggested that maternal nutritional status at conception may influence the total need for energy during gestation. Maternal fat deposition is obviously greater in well-fed women than in underfed women, and the well-fed women tend to have larger changes in basal metabolic rates leading to higher total energy needs.

Table

TABLE 3Recommended Protein Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 3

Recommended Protein Intakes for Nonpregnant and Pregnant Adolescents*

All of these studies of energy requirements during pregnancy have been done in mature women; no studies of the energy cost of pregnancy among adolescents are available. Measurements of energy expenditure of pregnant adolescents, particularly the very young, are needed.

Protein

The additional need for protein during pregnancy is based on the amount of protein deposited in new tissue gained plus allowances for individual variability and the efficiency of conversion of dietary protein to tissue protein.1 Protein accretion tends to follow the pattern of fetal growth needs with much higher needs during late pregnancy than early pregnancy. The additional need for high-quality protein (ie, about two thirds from animal sources) is 1.3, 6.1, and 10.7 g/day during the first, second, and third trimesters of pregnancy, respectively. To allow for the uncertainty about the rate of tissue deposition, an additional allowance of 10 g/day is recommended, or a total of 60 g/day throughout pregnancy (Table 3). The previous edition of the Recommended Dietary Allowances11 recommended 30 g protein/day for pregnant women. The revised allowance reflects a change in theory regarding the basis for protein requirements rather than new evidence. In the earlier edition, the allowance was based on nitrogen balance study results; the present edition1 is based on a summation of total protein deposition, or a factorial approach.

Usual protein intakes of pregnant women in the United States are above recommended levels and range from 75 to 110 g/day.2 Low-income women registering for the Supplemental Food Program for Women, Infants, and Children reported intakes of 74 g/day, even before participation in the program.12 An inadequate energy intake may cause a secondary protein deficiency if there is compensatory catabolism of protein and amino acids to meet energy needs. The adequacy of dietary protein intake needs to be considered in the context of total energy intake. Generally, protein should provide about 15% of the total energy.

Table

TABLE 4Recommended Vitamin Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 4

Recommended Vitamin Intakes for Nonpregnant and Pregnant Adolescents*

Use of specially formulated protein supplements (eg, protein powders) is not necessary or recommended for pregnancy.2 Rush and colleagues13 reported an inverse relationship between birth weight and protein density in supplements. In general, the birth-weight changes were small, 30 g to 100 g, and the biological significance was uncertain. The design of the studies makes it impossible to determine if the effect was caused by protein or other nutrients in the supplement. A moderate increase in the use of food sources of protein, such as whole grains, milk, and legumes, as part of a balanced diet is the preferred way to meet protein requirements during pregnancy.

Elimination of all sources of animal protein from the diet may place the woman at risk for not meeting requirements of protein and other micronutrients. In that case, a vitamin-mineral supplement that provides nutrients most likely to be low should be recommended.

Vitamins

Because many vitamins function as co-factors for enzymes involved in the release of energy from carbohydrate, protein, and fat, the dietary need for vitamins is higher during pregnancy than in the nonpregnant state. Recommended intakes for all of the vitamins except vitamins A and D are increased, therefore, during pregnancy (Table 4). In the 1989 edition of the Recommended Dietary Allowances,1 the recommendations for vitamin C, vitamin B6, folacin, and vitamin B12 were lowered. The basis for these changes is reviewed below.

Vitamin C. The recommended intake of nonpregnant adults and adolescents over 15 years of age is 60 mg/day; younger adolescents are recommended to consume 50 mg/day. An increment of 10 mg/day is added to pregnancy to offset losses from the mother's body pool to the fetus during pregnancy (Table 4). This is half the amount recommended previously. The lower recommendation is based on the fact that the incremental need of the fetus near term is likely to be small, about 3 to 4 mg/day. Cigarette smokers use ascorbic acid at an increased rate. It is recommended that all pregnant women who smoke should consume at least 100 mg of vitamin C daily.1 Heavy users of alcohol, street drugs, oral contraceptives, and aspirin also may benefit from an increased intake of vitamin C. A number of persons routinely ingest large amounts of vitamin C. Because the vitamin is actively transported from placental to fetal blood, megadoses taken during pregnancy could lead to markedly elevated levels in the fetus.2 There is one anecdotal report of fetal vitamin C dependency thought to be induced in utero by excessive intakes of the vitamin.14

Vitamin B6. The requirement for vitamin B6 increases as the intake of protein increases, probably because vitamin B6 is required for normal amino acid metabolism. In the previous edition, the recommended dietary allowance (RDA) for vitamin B6 was estimated to be 0.02 mg/g protein.11 Based on new studies of vitamin B6 requirements, the value was lowered to 0.016 mg/g protein in the 1989 edition1 (Table 4). The vitamin B6 RDA is established in relation to the upper boundary of acceptable values, or approximately twice the minimum requirement. The extra allowance of 0.7 to 0.8 mg vitamin B6 in pregnancy is more than adequate for the incremental 10 g of protein recommended.

Positive associations between maternal vitamin B6 status and the course and outcome of pregnancy have been reported, but the results are not definitive because the studies did not include placebo groups nor were the studies randomized or blinded.2 For example, it has been claimed that vitamin B6 supplementation is effective in treating nausea and vomiting experienced during pregnancy, gestational diabetes, and "pregnancy depression." Three reports15-17 have related low vitamin B6 intakes and low plasma concentrations as well as low plasma pyridoxal phosphate levels at delivery to unsatisfactory Apgar scores in newborns. Maternal pyridoxine supplementation was associated with improved Apgar scores at 1 minute, but not at 5 minutes, which may be a measure more indicative of long-term infant health.17 Since most clinical trials have failed to demonstrate a positive impact of vitamin B6 supplementation on pregnancy outcome, routine supplementation is not recommended for pregnancy.2 Pregnant adolescents are at high risk for inadequate intakes, however, and a supplement containing 2 mg of vitamin B6 is recommended for this group.

Folacin. New data show that the dietary need to maintain liver folacin stores is lower than originally estimated.1 The RDA is thought to be approximately 3 μg/kg body weight or 180 μg/day for nonpregnant adolescents over 15 years of age and 150 μg/day for those under 15 years (Table 4). On the basis of a 50% food folate absorption, the RDA for folate was set at 400 μg/day during pregnancy. This should provide the 200 μg/day shown to prevent folate deficiency in women who started pregnancy with moderate folate stores.1 The recommended folacin intake can be provided by a diet composed of fortified or whole grain breads and cereals, dried peas and beans, leafy vegetables, and fruit.

Mild to moderate folate deficiencies, as assessed by biochemical measurements of folate concentrations in serum or erythrocytes, have been associated with spontaneous abortion, preterm delivery, fetal malformations, and low birth weight. In July 1992, the Centers for Disease Control and Prevention recommended that all women of childbearing age take supplemental folate. This recommendation was based on accumulating epidemiological evidence that folate supplementation reduced the occurrence of neural tube defects. The experiments do not show, however, that this association is due to a primary folic acid deficiency.

Vitamin B12. The 1989 vitamin B12 RDA for nonpregnant women is 2 μg/day, down from 3 μg/day in 1980 (Table 4). The lower recommendation reflects a more conservative attitude toward maintenance of a vitamin B12 body pool. The demand for vitamin B12 by the fetus is thought to be small, only 0.1 to 0.2 μg/day. Previously, an additional 1 μg/day was recommended for pregnancy; in 1989, an increment of only 0.2 μg/day was recommended. Deficiency of vitamin B12 is occasionally observed in vegans (ie, complete vegetarians) who have followed this lifestyle for many years. In a few cases, infants born to mothers who were complete vegetarians developed signs of vitamin B12 deficiency within the first couple months of life.2 It is recommended that complete vegetarians take a daily vitamin B12 supplement that provides 2 μg/day or seek food sources to which vitamin B12 has been added.

Table

TABLE 5Recommended Mineral Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 5

Recommended Mineral Intakes for Nonpregnant and Pregnant Adolescents*

Other Vitamins. Surveys of the nutrient intake of pregnant adolescents often show that intakes of vitamin D and E are below the amount recommended. Routine supplementation of these two vitamins is not recommended, however. In most regions of the United States, vitamin D status is maintained by good exposure to sunlight. Reported intakes of vitamin E range from 30% to 90% of the recommended intake. These estimates of intake may be low, however, because the dietary supply of vitamin E is difficult to assess. Food composition data are poor, and reported intake of fat and oil, the major sources of vitamin E in the diet, may be underestimated. Biochemical or clinical signs of low intakes of vitamins D and E among pregnant women in the United States are reported infrequently.

Minerals

The intake of three minerals, zinc, calcium, and iron, by pregnant adolescents tends to be less than the amounts recommended.2 Zinc intake averaged about 6 mg, or 40% of the RDA, calcium about 870 mg, or 72% of the RDA, and iron about 15 mg, or 50% of the RDA. One should keep in mind, however, that the number of women studied is very small and that there were wide differences among the intakes reported.

Zinc. Zinc is essential for normal protein synthesis. Prior to 1989, 20 mg zinc/day was recommended for all pregnant women. This was based on the amount of lean tissue gained during pregnancy and the concentration of zinc in lean tissue, 30 μg/g. That recommendation was lowered to 15 mg/day in the 1989 RDAs1 (Table 5). The previous recommendation had assumed that the entire amount of weight gained during pregnancy is lean tissue. Because a significant proportion of the weight gain is fat or water, it is reasonable to lower the recommended increment for pregnancy. The present recommendation is based on the zinc content of the tissues gained during pregnancy.18 Zinc requirements are highest in the third trimester when the fetus acquires two thirds of its zinc content.

Low concentrations of zinc in the plasma have been associated with complications of pregnancy, such as pregnancy-induced hypertension, prolonged labor, intrapartum hemorrhage, intrauterine growth retardation, and congenital malformations.18 However, there has been a lack of consistency across studies, and zinc supplementation studies have not always yielded positive results. Consequently, supplemental zinc is not routinely recommended for pregnant women. Treatment of iron-deficiency anemia with therapeutic doses of supplemental iron, ie, greater than 100 mg iron/day, may impair zinc absorption.2 Women treated for iron-deficiency anemia should receive supplements of zinc as well as supplements of iron.

Calcium. To provide sufficient calcium for fetal bone mineralization and protection of the maternal skeleton, 1200 mg calcium/day is recommended for pregnant women1 (Table 5). This is equivalent to the amount recommended for nonpregnant adolescents and young adults; no additional allowance is made for pregnancy for these young women. It is thought that the additional needs for pregnancy will be met by improved use of dietary calcium. Serum 1,25 dihydroxy vitamin D concentrations double in late pregnancy,19 and this is probably associated with an increase in calcium absorption.

Dietary surveys show that pregnant women, on the average, drink more milk than nonpregnant or lactating women.2 Total calcium intake, however, still remains below recommended levels. Adverse consequences of low calcium intakes during pregnancy have not been documented, although there is some evidence that supplemental calcium reduces the incidence of pregnancy-induced hypertension and preeclampsia during pregnancy.20 There is concern that bone mineralization may be impaired in pregnant women under 25 years of age who are consuming low calcium diets (ie, less than 600 mg/day). It is prudent, therefore, for younger women with low calcium intakes to either increase their intake of food sources of calcium, such as milk or cheese, or to add a supplement that provides about 600 mg/day.2

Iron. Iron is essential for tissue growth and expansion of the red cell mass during adolescent growth. Pregnancy among adolescents will further increase the need for iron for fetal growth and expansion of the maternal circulating hemoglobin mass. The recommended intake of iron by girls between 11 and 18 years of age is 15 mg/day; this is doubled to 30 mg/day if the adolescent becomes pregnant (Table 5). This recommendation cannot be met by the iron content of habitual US diets. Supplemental iron is needed, therefore, to meet the RDA for pregnancy.

Results from the second National Health and Nutrition Examination Survey showed that 5% to 10% of the nonpregnant women of childbearing age in the United States suffer from iron deficiency. Worldwide surveys suggest that the prevalence may rise to as much as 35% to 50% of the pregnant women because of the high demand for iron during gestation.2 In general, hemoglobin concentrations tend to be lower among unsupplemented pregnant women than among supplemented women, suggesting that hemoglobin production is impaired because of a lack of iron in the unsupplemented group. Teenagers may have an even greater risk of iron deficiency because of the high iron requirements imposed by their recent growth spurt. To prevent iron deficiency, routine use of 30 mg of ferrous iron per day is recommended for all pregnant women beginning at about week 12 of gestation.2 This supplemental iron should be taken between meals with liquids other than milk, tea, or coffee to ensure good absorption.

NUTRIENT SUPPLEMENTATION FOR PREGNANT ADOLESCENTS

The eating behaviors, food preferences, and lifestyle of adolescents make this population particularly vulnerable for nutritional problems. Dieting and weight concerns, irregular meals, and snacking habits are all associated with poor overall diet quality. Those who have had a recent weight loss and who have a BMI of less than 19.8 should be evaluated for an eating disorder. Cigarette smoking or abuse of alcohol or street drugs may further increase the risk of nutrient deficiencies. Finally, the presence of a poor socioeconomic status, strained family relationships, loneliness, and isolation can exacerbate poor dietary habits. The dietary practices of all pregnant adolescents, therefore, should be assessed to determine the need for dietary counseling and vitamin-mineral supplements.

For the pregnant adolescent who does not ordinarily consume an adequate diet, a daily vitamin-mineral supplement containing the following nutrients should be recommended:

* iron, 30 mg

* zinc, 15 mg

* coppen 2 mg

* calcium, 250 mg

* vitamin B6, 2 mg

* folate, 300 μg

* vitamin C, .50 mg

* vitamin D, 5 μg (200 IU)

For best resorption of these nutrients, the supplement should be taken between meals or at bedtime.

Additional iron is required if iron deficiency is diagnosed. A hemoglobin concentration <11 g/dL during the first or third trimesters or <10.5 g/dL during the second trimester is defined as anemia. Anemia accompanied by a serum ferritin concentration of less than 12 μg/dL can be presumed to be iron-deficiency anemia and requires treatment with 60 to 120 mg of ferrous iron daily. When the hemoglobin concentration returns to normal for the stage of gestation, the dose can be decreased to 30 mg/day.2 To enhance the use of additional iron prescribed for treatment of iron-deficiency anemia, it is advisable to take the supplement separately from other vitamin-mineral supplements either between meals or at bedtime.

Additional vitamin-mineral supplements may be recommended in special circumstances. For example, vegetarians who do not include any animal protein products in their diets should be given 2 μg vitamin B12/day and 10 μg (or 400 IU) of vitamin D. Also, those adolescents consuming less than 600 mg calcium/ day should be given a calcium supplement that provides 600 mg. Unlike iron, calcium absorption is enhanced when the supplement is taken with meals rather than between meals.

SUMMARY

The nutritional needs of pregnant adolescents are the greatest at a time when it is most difficult to meet them. Dieting, skipping meals, snacking, eating away from home, consuming fast foods, and trying unconventional diets are common eating behaviors among adolescents, which relate to their changing lifestyles of increased independence, busy schedules, search for self-identity, peer influence, group conformity, and body image dissatisfaction. Total nutritional needs of pregnant adolescents who are at least 2-years post-menarche are similar to those of pregnant adults. But, because of their poor dietary habits, they usually enter pregnancy with reduced nutrient stores and increased risk of nutritional deficiencies. All pregnant teens, therefore, should have their dietary habits assessed along with special dietary counseling, and vitamin-mineral supplements should be recommended if their usual nutritional intake is below standard. Also, the weight-gain pattern should be monitored to ensure that energy intakes are sufficient to support a gain of about 0.4 kg (1 lb) per week in the second and third trimester.

REFERENCES

1. National Research Council, Food and Nutrition Board. Recommended Daily Allowances. 10th ed. Washington, DC: National Academy Press; 1989.

2. Institute of Medicine, National Academy of Sciences, Food and Nutrition Board. Nutrition During Pregnancy. Part I: Weight Gam. Part II: Nutrient Supplements. Washington, DC: National Academy Press; 1990.

3. Rosso P. Nutrition and Metabolism in Pregnancy. Mother and Fetus. New York, NY: Oxford University Press; 1990.

4. Garn SM, La Velie M, Pesick SD, Ridella SA. Are pregnant teenagers still in rapid growth? Am J Dis Child. 1984;130:32-34.

5. Frisancho AR, Matos J, Leonard WR, Yaroch LA. Developmental and nutritional determinants of pregnancy outcome among teenagers. Am J Phys Anthrapol. 1985;66:247-261.

6. Frisancho AR, Matos J, Flegel P. Maternal nutritional status and adolescent pregnancy outcome. Am J Clin Nutr. 1983;38:739-746.

7. Meserole LP, Worthington-Roberts BS, Rees JM, Wright LS. Prenatal weight gain and postpartum weight loss patterns in adolescents. J Adolesc Health Care. 1984;5:21-27.

8. Hediger ML, Schnoll TO, Belsky DH, Anees IG, Salmon RW. Patterns of weight gain in adolescent pregnancy: effects on birth weight and preterm delivery. Obstet Gynecol. 1989;74:6-12.

9. Hytten FE. Weight gain in pregnancy. In: Hytten FE, Chamberlain G, eds. Clinical Physiology in Obstetrics. Oxford, England: Blackwell Scientific Publications; 1980.

10. Durnin JVGA. Energy requirements of pregnancy and integration of the longitudinal data from the five country study. Lancet. 1987;2:1131-1133.

11. National Research Council, Food and Nutrition Board. Recommended DaAy Allowances. 9th ed. Washington, DC: National Academy of Sciences; 1980.

12. Rush D, Sloan NL, Leighton J, et al. The national WIC evaluation: evaluation of the Special Supplemental Food Program for Women, Infants, and Children, V; longitudinal study of pregnant women. Am J Clin Nutr. 1988;48:439-483.

13. Rush D, Kristal A, Navarro C, et al. The effects of dietary supplementation during pregnancy on placental morphology, pathology, and histomorphometry. Am J Clin Nutr. 1984;39:863-871.

14. Cochrane WA. Overnutrition in prenatal and neonatal life: a problem? Can Med Assoc J. 1965;93:893-899.

15. Roepke JLB, Kirksey A. Vitamin B6 nutritine during pregnancy and lactation, I: vitamin B6 intake, levels of the vitamin in biological fluids, and condition of the infant at birth. Am J Clin Nutr. 1979;32:2249-2256.

16. Schuster K, Bailey LB, Mahan CS. Vitamin B6 status of low-income adolescent and adult pregnant women and the condition of their infants at birth. Am J Clin Nutr. 1981;34:1731-1735.

17. Schuster K, Bailey LB, Mahan CS. Effect of maternal pyridoxine-HC1 supplementation on the vitamin B6 status of mother and infant and on pregnancy outcome. J Nutr. 1984;114:977-988.

18. Swanson CA, King JC. Zinc and pregnancy outcome. Am J Clin Nutr. 1987;46:763-771.

19. King JC, Halloran BP, Huq N, Diamond T, Buckendahl PE. Calcium metabolism during pregnancy and lactation. In: Piccano MF, Lonnerdal B, eds. Mechanisms Regulating Lactation and Infant Nutrient Utilization. New York, NY: Wiley-Liss Inc; 1992:129-146.

20. Myatt L. The relation of calcium nutrition and metabolism to preeclampsia and premature labor. In: Tsang RC, Mimouni F, eds. Calcium Nutriture for Mothers and Children. Carnation Nutrition Education Series. Vol 3. New York, NY: Raven Press Ltd; 1992:129-141.

TABLE 1

Gestational Weight-Gain Recommendations for Adolescents *†

TABLE 2

Recommended Energy Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 3

Recommended Protein Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 4

Recommended Vitamin Intakes for Nonpregnant and Pregnant Adolescents*

TABLE 5

Recommended Mineral Intakes for Nonpregnant and Pregnant Adolescents*

10.3928/0090-4481-19930201-07

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