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1
Summary
In the 20 years since publication of the Food and Nutrition Board's
landmark report Matemal Nutr'izon and the Course of Pregnancy (NRC,
1970), the fields of nutrition and obstetrics have changed greatly. These
changes, many of them stimulated by the report itself and the work of suc-
cessor committees of the board and of the Institute of Medicine, include
expanded private and governmental research efforts, enhanced teaching
of perinatal nutrition to students in the health care professions, and a
resurgence of interest in applied nutrition by clinicians in obstetrics and
pediatrics. Also during the period, the Supplemental Food Program for
Women, Infants, and Children (WIC) was established in the U.S. Depart-
mentofAgriculture; the reports Preventing Low Birthweight (IOM, 1985)
and Prenatal Care (IOM, 1988) were published by the Institute of Medicine;
the National Commission for the Prevention of Infant Mortality was estab-
lished; and the report Caring for Our Future: The Content of Prenatal Care
was released by the Public Health Service (DHHS, 1989~. All these events
have underscored the importance of nutrition during pregnancy and the
perinatal period.
Greater visibility of maternity services in the United States has also
drawn attention to many gaps and weaknesses in knowledge about maternal
nutrition and about how recent findings should be applied in prenatal
care. To address these deficiencies, the Food and Nutrition Board (FNB)
established the Committee on Nutritional Status During Pregnancy and
Lactation late in 1987 to conduct a detailed assessment of the published
data. The committee addressed its task by forming three subcommittees:
1
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2
SUMAL4RY
Nutritional Status and Weight Gain During Pregnancy, Dietary Intake and
Nutrient Supplements During Pregnancy, and Nutritional Status During
Lactation. The parent committee, in addition to coordinating the work of its
subcommittees, has maintained close liaison with the FNB's Subcommittee
on the Tenth Edition of the Recommended Dietary Allowances in order to
maintain consistency in the work of the two groups.
In general, the committee found few well-designed studies and little
scientific evidence regarding many important issues. For this reason, areas
needing further research are underscored in this publication. Careful
attention to the information in these reports should help stimulate both
research and practice toward a common goal of improving the health and
well-being of mothers and children in the United States.
This publication includes two reports. Part I is a critical evaluation of
the data concerning nutritional status and weight gain during pregnancy.
Part II contains an examination of the evidence on the need for nutrient
supplements during pregnancy. A second publication covering nutrition
during lactation will be released in late 1990. Each of these reports
responds to specific requests from the Bureau of Maternal and Child
Health and Resources Development of the U.S. Department of Health and
Human Services, which funded the study. The committee anticipates that
material presented in the three reports will serve as a basis for additional
publications that provide a comprehensive, practical approach for delivering
nutritional care curing pregnancy and lactation.
PART I: NUTRITIONAL STATUS AND WEIGHT GAIN
The overall goals of the Subcommittee on Nutritional Status and
Weight Gain During Pregnancy were to analyze the scientific evidence per-
taining to weight gain during pregnancy and to formulate recommendations
for healthy gestational weight gain. The subcommittee was asked to address
the following questions:
.
How do nutritional status prior to pregnancy and dietary intake
during gestation influence the pattern and total amount of weight gain?
· Which, if any, anthropometric measurements are useful in assessing
nutritional status during pregnancy?
· How should weight gain recommendations be modified for pregnant
women of black, Hispanic, and Southeast Asian origin and for those under
age 20 or over age 35?
Part I deals only to a limited extent with nutritional care during
pregnancy. It does not include many other elements of prenatal nutrition
services, such as the evaluation and improvement of the nutritional quality
of diet (briefly covered in Part II of this volume), and the importance of
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SUMAL4RY
access to a regular and adequate supply of nutritious foods, development of
sound eating practices for the family, dietary adjustments for mothers with
acute and chronic medical conditions, and breastfeeding promotion and
education. Although the subcommittee limited its review to its charge, it
recognized that such a broad spectrum of nutrition services is an important
part of comprehensive maternal health care.
The subcommittee began its work by tracing trends in selected aspects
of prenatal care, maternal nutritional status, and the course and outcomes of
pregnancy (e.g., fetal growth, birth weight, postpartum weight retention). It
then undertook its major effort-an extensive critical review of the scientific
literature. Epidemiologic and clinical evidence pertaining to determinants
of weight gain and effects of weight gain on maternal and child health
were examined. This included consideration of total gain, pattern of gain,
and composition of the added tissue. The practicality and usefulness of
anthropometric measurements in the clinical setting were assessed. The
subcommittee paid close attention to new analyses from the 1980 National
Natality Survey, which provides the only recent nationally representative
U.S. data on weight gain during pregnancy, infant birth weight, and an
assortment of maternal characteristics.
Most of the literature reviewed pertained to women living in industri-
alized nations. Data were more complete for whites than for nonwhites.
The conclusions and recommendations presented in this report relate to
healthy women in the United States; they have not been evaluated with
respect to women in less developed countries or women who have recently
emigrated from those countries to the United States.
The subcommittee took particular care in clarifying its definitions and
in examining the strengths and limitations of study methods. For example,
the term prepreg~ancy nutritional status can have many meanings. The
subcommittee agreed that prepregnanc~y weight for height is the simplest
and most useful index for evaluating prepregnancy nutritional status in
the clinical setting, while recognizing that this is an indirect measure of
energy stores only. The measurements are relatively easy to make, and the
approach provides a systematic method for distinguishing between women
who weigh more because of their greater height and those whose greater
weight reflects extra fat or lean body mass. Much more complex methods
are required for defining other aspects of nutritional status. However,
weight for height is applicable to most studies that address gestational
weight gain.
The meaning of gestational weight gain also received the subcommit-
tee's attention. Comparisons among studies are complicated by the many
different methods used to compute gestational weight gain. In this report,
three types of gestational weight gain are discussed in detail, namely:
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4
SUMMARY
· total weight gain (weight just before delivery minus weight just
before conception);
net weight gain (total weight gain minus the infant's birth weight);
and
rate per week (weight gained over a specified period divided by the
duration of that period in weeks).
Attention is also given to different methods of comparing weight gain with
standards in both clinical and research settings.
The subcommittee considered gestational weight gain in relation to
clinical care and to several maternal and infant outcomes, especially to
birth weight. The emphasis on birth weight reflects its importance for child
mortality, morbidity, and physical and mental performance. There is a
relative lack of studies relating gestational weight gain to other important
maternal and child health outcomes.
A central question is whether or not gestational weight gain is causally
associated with pregnancy outcomes such as fetal growth and postpartum
retention of adipose tissue. Potential causal relationships were examined
by applying standard epidemiologic terms and concepts to characterize the
relationships between maternal factors, nutritional intervention, gestational
weight gain, and maternal and child health.
Factors that investigators have linked with gestational weight gain
include maternal prepregnancy weight for height, prepregnancy weight,
maternal height, ethnic background, age and parity, cigarette smoking,
socioeconomic status, and energy intake. Analyses of data from the 1980
National Natality Survey made it possible to examine whether specified
maternal characteristics are independently associated with weight gain. For
example, the association between smoking and gestational weight gain
can be tested while holding constant prepregnancy weight for height, ethnic
origin, and other factors. However, even this large, relatively representative
data set was not big enough for an examination of all the relationships of
interest, such as the association of Hispanic origin with weight gain in obese
women.
For certain analyses of data from the 1980 National Natality Survey,
the subcommittee used a gestational duration of 39 to 41 weeks and a live
birth weight of 3 to 4 kg as an operational definition of favorable pregnancy
outcome (recognizing that a small percentage of such infants may have
serious birth defects or other health problems). The use of this range for
birth weight represents a balance between the benefits of increased fetal
growth for the infant, on the one hand, and the possible risks to the mother
and infant of complicated labor and delivery with high birth weight (>4
kg), on the other.
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SUMMARY
s
Historical Perspective
Between the 196Os and 1980s, it gradually became common to recom-
mend a gestational weight gain averaging 11 kg (24 lb) or more, rather than
the 8 to 9 kg (18 to 20 lb) or less recommended previously. This change was
accompanied by a 50% increase in gestational weight gain. Between 1971
and 1980, mean birth weight increased by approximately 60 g for whites
and 30 g for blacks, low birth weight (<2.5 kg) prevalence was reduced
by about 20% for whites and 7% for blacks, and the high birth weight
prevalence increased by 30% for whites and by 15% for blacks. Several
factors that may also have contributed to fetal growth or gestational weight
gain during the period include increased prepregnancy weight, increased
height, decreased smoking during pregnancy, increased participation in the
WIC program, and earlier prenatal care.
Conclusions on Weight Gain During Pregnancy
Assessment of Weight and Weight Gain
Prepregnancy weight-for-height and serial weight measurements are
the only anthropometric measurements with documented clinical value
for assessment of gestational weight gain. In the clinical setting, it is
difficult for different individuals or even for the same person to obtain
reproducible measurements of skinfold thicknesses. Even those skinfold
thickness measurements that are reliable are not useful clinically, because
there are no properly validated equations that use skinfold thicknesses
to predict the total body composition of pregnant women, nor are there
reference standards for skinfold thickness measurements validated against
fetal outcomes.
Body mass index (BMI), defined as weight/height2, is a better indicator
of maternal nutritional status than is weight alone. The subcommittee used
metric units (kilograms and meters) to calculate the BMIs used in this
report. Weight for height expressed as a percentage of a standard is also
usable. Since none of the weight-for-height classification schemes has been
validated against pregnancy outcome, any cutoff points will be arbitrary for
women of reproductive age. However, the subcommittee agreed on the
following weight-for-height categories:
· underweight: BMI <19.8
· normal weight: BMI 19.8 to 26.0
· overweight: BMI >26.0 to 29.0
· obese: BMI >29.0
The cutoff points generally correspond to 90, 120, and 135% of the 1959
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SUMMARY
Metropolitan Life Insurance Company's weight-for-height standards (Met-
ropolitan Life Insurance Company, 1959)-the standards which have been
in most common use in the United States.
Although specific weight gain grids have substantial limitations, most
are useful in the clinical setting because they permit visual tracking of weight
gain by week of gestation. That is, they provide the practitioner with a
visual impression of the progress of weight gain and simplify detection
of an abnormal change in weight over time. Studies indicate that after
the first trimester, the typical pattern of weight gain is one of gradual,
steady increments, but definitive studies have not yet been conducted to
determine what rates of gain are most desirable for favorable maternal
and fetal outcomes and whether the optimal pattern of gain varies over
the second and third trimesters. The subcommittee concluded that heavy
emphasis should be placed on identifying major deviations in the rate of
gain that may signal problems and warrant further assessment, as opposed
to deviations related to errors in measurement or recording or to common
shifts in weight related to fluid changes, contents of bladder and bowel,
clothing, and time of day. Deviations from the expected pattern of weight
gain may be entirely unrelated to nutrient intake and energy balance but,
rather, may be related to such factors as those listed above.
Gestational weight gain is normally attributable to increases in both
lean and fat tissue of the mother and the fetus as well as to water retention.
Most methods for assessing body composition (e.g., underwater weighing
and total body water) are based on assumptions that have not been vali-
dated for pregnant women and that may not be applicable because they
do not distinguish between the added maternal and fetal tissues. As a re-
sult, different methods-yield inconsistent results when applied in a research
setting to the same population of pregnant women. Smooth, progressive
weight gain generally represents a gain of lean and fat tissue, whereas errat-
ically high weight gain is likely to represent excessive fluid retention. The
clinical determination of ankle or leg edema (which worsens on standing)
or generalized edema (which is not dependent on body position) can be
useful in identifying extra fluid retention. However, it provides insufficient
quantitative information about the amount of fluid that has been gained.
Determinants of Gestational Weight Gain
Prepregnancy weight for height is a determinant of gestational weight
gain. On average, women who are overweight at conception (i.e., women
whose BMI exceeds 26.0) gain less weight during pregnancy than do thinner
women. However, there is wide variation in weight gain by women with
normal pregnancies within each prepregnancy weight-for-height category.
The variation is highest among obese women (BMI >29.0~.
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SUMMARY
7
. .
Some of the other maternal characteristics associated with an increased
risk of low gestational weight gain (less than 7 kg, or 16 lb) occur in
combination, e.g., low family income, black race, young age, unmarried
status, and low educational level. These characteristics are also associated
with shortened gestational duration. Studies using analytic methods to
control for gestational duration and other factors suggest that black women
are more likely to have low weight gain than are white women, but the
reason for this difference is not known. Some ethnic groups with small
average body size (e.g., Southeast Asians) have been reported to have
low average weight gains, but the clinical significance of this has not been
established.
In studies of groups of women in the United States and elsewhere,
energy intake is a determinant of gestational weight gain, but the reported
relationship is weak. Changes in energy intake during pregnancy are difficult
to detect because they are relatively small, on average, and current dietary
assessment methods are rather imprecise. Variation in energy intake during
pregnancy is determined largely by body size and the level of physical
activity, not by gestational weight gain. Furthermore, energy intake may
erroneously appear to be relatively unimportant for gestational weight gain
if women expend less energy by decreasing their physical activity. Overall,
however, there is no question that restriction of energy intake can limit
weight gain or that excessive energy intake leads to extra fat storage.
The impact of food supplementation on gestational weight gain (and
fetal growth) appears to depend on the prior energy deficit of the woman
and the extent to which the supplement makes up for the deficit between
usual energy intake and requirements. That is, the impact is greater in
women with low prepregnancy weight for height or in women whose food
intake has been restricted.
Consequences of Gestaizonal Weight Gain
Wide variation is seen in weight gains among women giving birth to
live, optimally grown (i.e., 3 to 4 kg at 39 to 41 weeks of gestation) infants.
For example, in the United States in 1980, the 15th and 85th percentiles of
weight gain were 7.3 and 18.2 kg (16 and 40 lb), respectively, for normal-
weight women who delivered babies with these characteristics. This wide
variation indicates that many factors in addition to weight gain during
pregnancy contribute to a favorable outcome. Nevertheless, a large body
of evidence indicates that gestational weight gain, particularly during the
second and third trimesters, is an important determinant of fetal growth.
Low gestational weight gain is associated with an increased risk of giving
birth to a growth-retarded infant. This has important adverse consequences
for subsequent somatic growth and, possibly, neurobehavioral development,
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SUMMARY
and it increases the risk of infant mortality. (More direct evidence also
indicates a link between low weight gain and fetal and infant mortality.)
The effect of first-trimester weight gain or weight loss on fetal growth is
less clear, because the weight change is usually small, and because very few
studies have included women in this trimester of pregnancy.
The effect of gestational weight gain on fetal growth is modified
by the mother's prepregnancy weight for height. Several epidemiologic
studies, including the 1980 National Natality Survey, have convincingly
demonstrated that the effect of a given weight gain (or rate of weight
gain) is greatest in thin women and least in overweight and obese women.
However, prepregnancy weight for height is a determinant of fetal growth
above and beyond the effect of gestational weight gain: 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. Since
higher birth weights generally present lower risks for the infants, desirable
weight gains for thin women are higher than those for normal-weight
women, whereas desirable weight gains for overweight and obese women
are lower. Among obese women, the measured effect of weight gain on
birth weight is weak.
Most epidemiologic evidence suggests that maternal age does not
modify the effect of weight gain on fetal growth. Very young adolescents
(less than 2 years postmenarche) may, however, give birth to smaller infants
for a given weight gain than do older women. Although the limited data
indicate no clear modification of the effect by racial or ethnic background,
black infants tend to be smaller than white infants for the same gestational
weight gain of the mothers. Young girls and black women should therefore
strive for weight gains toward the upper end of the ranges otherwise
recommended for women with similar weights for height.
Data concerning the effect of changes in maternal body composition
on fetal growth are meager and inconclusive. Studies suggest that increases
in maternal fat, lean tissue, and body water may each be associated with
increased fetal growth.
Very high gestational weight gain is associated with an increased rate
of high birth weight which in turn is associated with some increase in the
risk of fetopelvic disproportion, operative delivery (forceps or cesarean
delivery), birth trauma, and asphyxia and mortality. These associations
appear to be more pronounced in short women, i.e., <157 cm (62 ink. A
lower ceiling on weight gain may therefore be preferable in short women
at any given weight for height.
Energy supplementation of pregnant women whose usual energy in-
take is low relative to their needs may result in slightly higher average
birth weights and decreased incidence of intrauterine growth retardation,
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SUMMARY
9
although concurrent increases in gestational weight gain have not always
been observed.
Several, but not all, reports suggest that low rates of gestational
weight gain are associated with a shorter mean gestational duration and an
increased risk of preterm delivery. Difficulties in determining the length
of gestation and assessing weight gain patterns prevent firm inferences,
however.
Gestational weight gain does not seem to be an important determi-
nant of spontaneous abortion (miscarriage), congenital anomalies, maternal
mortality, pregnancy-induced hypertension and preeclampsia, or volume or
composition of milk produced during lactation. However, a sharp increase
in weight accompanied by generalized edema and an elevated blood pres-
sure remain the hallmarks of preeclampsia, a complication of pregnancy
that requires immediate attention.
On average, each successive birth adds about 1 kg (2.2 lb) of postpar-
tum body weight above that normally gained with age. This gain is likely
to be surpassed, however, in women with high gestational weight gains.
In women carrying multiple fetuses, mean gestational weight gain
appears to be greater by an amount larger than that accounted for by the
weight of the additional fetuses and support tissues. In twin pregnancies,
increased maternal weight gain also appears to be associated with increased
birth weight.
Clinical Recommendations
The following recommendations are based largely on observational
studies of weight gains in large groups of women and an attempt to balance
the benefits of increased fetal growth with the risks of complicated labor and
delivery and of postpartum maternal weight retention. In the absence of
definitive data regarding optimal gestational weight gain, the subcommittee
concluded that the target range for desirable maternal weight gain should
be based on prepregnancy weight for height and should include the mean
weight gain for women delivering full-term babies weighing between 3 and 4
kg. However, because the observed range for such mothers is too broad to
be useful clinically, the subcommittee used its judgment in setting narrower
target ranges by weight-for-height categories.
Measurement
Health care providers should adopt specific, reliable procedures for
obtaining and recording weight and height and should implement them
consistently in classifying women according to weight for height, setting
weight gain goals, and monitoring weight gain over the course of pregnancy.
Attention should be directed to the following elements:
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SUMMARY
TABLE 1-l Recommended Total Weight Gain Ranges
for Pregnant Women?a by Prepregnancy Body Mass
Index (BMI)b
Recommended Total
Gain
Weight-for-Height Category kg lb
Low (BMI < 19.8) 12.5-18 28~0
Normal (BMI of 19.8 to 26.0) 11.5-16 25-35
HighC (BMI > 26.0 to 29.0) 7-11.5 15-25
a Young adolescents and black women should strive for gains at
the upper end of the recommended range. Short women (<157 cm,
or 62 in.) should strive for gains at the lower end of the range.
b BMI is calculated using metric units.
c The recommended target weight gain for obese women (BMI >
29.0) is at least 6.8 kg (15 lb).
· Prior to conception use consistent and reliable procedures to ac-
curately measure and record in the medical record the woman's weight
and height without shoes. These are the preferred bases for calculating
prepregnancy weight for height.
· Determine the woman's prepregnancy BMI. The table in Appendix
C simplifies this calculation. The weight-for-height classifications shown in
Able 1-1 are recommended.
· Measure height and weight at the first prenatal visit carefully by
procedures that have been rigorously standardized at the site of prenatal
care. The initial weight measurement can be compared with prepregnancy
weight and provides the baseline for monitoring weight change over the
course of pregnancy. Measurement of height is recommended because
objective data on height are often not recorded in the medical record.
Use consistent, reliable procedures to measure weight at each
subsequent visit.
· Estimate the woman's gestational age from the onset of her last
menstruation, preferably supplemented by estimates based on the obstetric
clinical examination and, perhaps, by early ultrasound examination.
· Record weight in a table and plot it on a chart included in the
obstetric record, which should show the week of gestation on the hori-
zontal axis and weight on the vertical axis. The subcommittee developed
provisional charts (see Appendix B) showing the recommended target gain
as the end points and the recommended rate of gain as the slope. Until
a weight gain chart has been validated, the subcommittee favors use of
these provisional charts. A notation should be made if gestational age is
uncertain, since this can markedly affect placement of the woman's current
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SUMMARY
11
weight on the chart. The charts are not meant to imply that the weight
gain of all women of the designated BMI group should fall on the dashed
line. Rather, the rate of gain should approximately parallel that shown by
the dashed line.
Counseling
During pregnancy a woman may be particularly receptive to guidance
regarding behaviors that may influence her health and that of her devel-
oping fetus. The subcommittee recommends that women receive guidance
regarding a healthy diet that will promote adequate weight gain. Sound
dietary guidelines can be found in publications by federal agencies (e.g.,
DHHS/USDA/March of Dimes Birth Defects Foundation, 1982; USDA,
1979, 1989), by state agencies (e.g., Corruccini, 1977), and by private
sources (e.g., American Red Cross, 1984; Dimperio, 1988~.
· Set a weight gain goal together with the pregnant woman, prefer-
ably beginning at the comprehensive initial prenatal examination, and
explain to her why weight gain is important. This goal is best identified as
a range of desirable total gestational weight gain and the rate of such gain.
The subcommittee emphasizes use of a range rather than a single target
weight, because a wide range of gestational weight gains is compatible with
desirable pregnancy outcomes, because there is no method available for
establishing the ideal gestational weight gain for an individual woman, and
because a range rather than a single number may help alleviate exces-
sive concern about weight gain during pregnancy. All women should be
encouraged to gain enough weight to achieve at least the lower limit of
weight specified for their weight-for-height category in Table 1-1. 1b help
the woman achieve her weight gain goal, she should be given appropriate
counseling or referred (e.g., to a social worker, dietitian, or WIC) to pro-
mote consumption of a wholesome, balanced diet consistent with ethnic,
cultural, and financial considerations.
· Base the recommended range of total weight gain and pattern
of gain mainly on prepregnancy weight for height. The subcommittee
recommends that women of normal prepregnancy weight for height carrying
a single fetus aim for a weight gain of between 11.5 and 16 kg (25 and
35 lb). This range is higher than that recommended in previous Food and
Nutrition Board reports, which recommended a range of 9 to 11.5 kg (20
to 25 lb). The basis of this higher recommendation is the reduced risk of
delivering an infant with intrauterine growth retardation with higher weight
gains. However, the risk of maternal weight retention postpartum and fetal
macrosomia may increase with higher weight gains in this range.
A slightly higher target range of 13 to 18 kg (28 to 40 lb) is recom-
mended for women with a low prepregnancy BMI (<19.8~. For those with
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SUMMARY
· Identify the characteristics of women who would benefit from in-
creased energy intake.
· Examine the effects of energy intake and weight gain on maternal
and perinatal outcomes in markedly or moderately obese women.
· Explore the use of different measures of gestational weight gain
(e.g., net weight gain and rate of weight gain) in research on gestational
weight gain and pregnancy outcomes.
Basic Research
· Determine the incremental dietary energy needs for pregnancy by
measuring energy stores and expenditures over the course of gestation.
· Identify appropriate animal models to use in investigations of the
role of nutrition in human pregnancy, considering the number of fetuses,
type of placentation, maturity of the fetus at delivery, body composition,
and physiologic adaptations such as plasma volume expansion.
· Investigate the influence of energy intake and prepregnancy weight-
for-height status on patterns of gain of fat, lean, water, and total weight
by using longitudinal studies beginning before conception and continuing
throughout gestation. This requires research to develop new methods or
modify existing ones for measuring body composition accurately during
pregnancy
· Identify the hormonal and biochemical determinants of weight gain
pattern and composition.
Applied Research
· Develop and validate protocols and standards for use in the clinical
setting. For example, establish cutoff values for prepregnancy BMIs as they
relate to gestational weight gain and maternal and fetal outcomes.
Develop a clinically useful weight gain chart and validate it against
outcome data.
· Improve methods of prenatal nutritional surveillance for public
health purposes. For example, include prepregnancy weight and height
on birth certificates and standardize assessment and reporting instruments
used in government programs such as WIC.
· Test recommended ranges of gestational weight gain against out
comes.
Test the effectiveness of specific interventions that are used to
improve weight gain.
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SUM~fARY
15
PART II: DIETARY INTAKE AND NUTRIENT SUPPLEMENTS
In the United States, vitamin and mineral supplementation is common,
especially among pregnant women. The Subcommittee on Dietary Intake
and Nutrient Supplements During Pregnancy and the parent committee
consider food as the optimal vehicle for delivering nutrients and nutrient
supplementation as an intervention. As with other types of intervention, a
recommendation to supplement the diet with special vitamin, mineral, or
protein preparations should be based on evidence of a benefit as well as a
lack of harmful effects.
In addressing the advisability of supplementation, the subcommittee
first reviewed biochemical, anthropometric, clinical, and dietary methods
for measuring the adequacy of specific nutrients during pregnancy. It then
identified nutrients that can be provided in adequate amounts by dietary
means and those for which supplementation may be desirable. Special
attention was directed toward protein, folate, iron, zinc, calcium, and
vitamins that might exert toxic effects if taken in high doses. Evidence
was sought concerning special recommendations for pregnant women of
black, Hispanic, and Southeast Asian origin and for women in their teens
or over age 35. Evidence regarding the potential value of periconceptional
multivitamin supplements in the prevention of neural tube defects was
evaluated. The interaction of diet with use of tobacco, alcohol, and caffeine
was also reviewed. In view of the widespread use of marijuana, the epidemic
of cocaine use among women of childbearing years, and cocaine's major
adverse effects on health, the consideration of nonfood substances was
enlarged to include those illegal drugs.
Specific recommendations for nutrition counseling and other services
to help improve maternal and family food intakes are beyond the scope
of this report. Among the many sources of information on these topics
are the National Center for Education in Maternal and Child Health in
Washington, D.C., Cooperative Extension's Expanded Food and Nutrition
Education Program (operated at the county level), state WIC programs,
state departments of health, the American Red Cross, and the American
College of Obstetricians and Gynecologists.
Methodology
1b determine whether nutrient supplements should be recommended
during pregnancy, the subcommittee examined several lines of evidence.
These included the results of controlled experimental studies of nutrient
requirements of women, laboratory studies and functional tests of nutri-
ent status, epidemiologic studies linking diet or supplement use with various
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SUMMARY
pregnancy outcomes, dietary intake data, and in some cases, studies in which
animal models were used to examine the effects of nutrient deficiency or
excess.
In its initial deliberations, the subcommittee determined that it would
limit its review to trace elements and vitamins for which a human re-
quirement has been established and to calcium, magnesium, and protein.
Protein is not an ingredient of vitamin-mineral preparations but is avail-
able in special powders and formulas as a dietary supplement. Essential
micronutrients excluded from consideration were phosphorus, sodium, chlo-
ride, and potassium all of which are widely available in foods but are not
ordinarily included in multivitamin-mineral preparations.
Limitations in the Data
Maternal physiologic changes during pregnancy affect the results of
laboratory tests and of tests reflecting how well the body is functioning
(e.g., enzyme activity and cellular uptake of nutrients). Reference standards
and cutoff points for laboratory and functional tests are affected by normal
pregnancy to degrees that vary with the stage of gestation.
Review of dietary intake data provides one method of determining
which nutrients warrant close attention. Less likely candidates for routine
supplementation are nutrients consumed at levels close to the 1989 Recom-
mended Dietary Allowance (RDA) for pregnant women, especially if there
is no evidence that a sizable segment of the pregnant population has intake
falling substantially below the RDN On the other hand, average nutrient
intakes lower than the RDA were viewed as inadequate evidence to support
routine supplementation of pregnant women with that nutrient. Because
the RDAs for most minerals and vitamins include a wide margin of safety,
the needs of many pregnant women can be met with intakes below the
RDN Moreover, estimates of nutrient intake based on dietary intake data
are imprecise and tend to underestimate total food and nutrient intake.
The data indicate that, on average, dietary intake by pregnant women is
less than the RDA for eight nutrients: vitamins Be, D, E, and folate; iron;
zinc; calcium; and magnesium.
Since nutrient supplements typically contain multiple nutrients, there
is the potential for nutrient-nutrient interactions during absorption and
metabolism. An increase in the concentration of one nutrient may adversely
affect the availability, absorption, or utilization of other nutrients provided
by the supplement and by diet.
The use of such substances as tobacco, alcohol, caffeine or coffee,
marijuana, and cocaine may affect maternal nutrition in two general ways.
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SUMMARY
17
The substance may increase the actual need for one or more nutrients by
a variety of mechanisms, for example, by increasing urinary excretion, or it
may lead to undesirable changes in food and nutrient intake.
C?~terza Used in Formulating Recommendations
The subcommittee decided to recommend routine supplementation
only if the usual dietary intake of the nutrient is likely to be low enough
to limit the production of compounds essential for body function or to
adversely affect the health of the mother, fetus, or newborn and if sup-
plementation poses no known dangers for the mother or fetus. Data
on nutrient interactions were considered in formulating recommendations
for specific nutrients and combinations of nutrients. In the subcommit-
tee's view, dietary supplements should not replace dietary counseling or a
well-balanced diet. Improvement of diet quality through use of nutritious
foods is strongly preferred to supplementation. Foods supply energy and
essential nutrients not found in supplements, and there is less risk of unde-
sirable nutrient-nutrient interactions when nutrients are provided by foods.
Nonetheless, certain situations may warrant use of a multivitamin-mineral
supplement, as described later in this chapter.
Conclusions
The subcommittee concluded that evaluation of a pregnant woman's
dietary pattern by a food history or food frequency questionnaire, aug-
mented by questions about special problems or conditions that might affect
her dietary adequacy or needs, may provide the best information on which
to assess the need for nutrient supplementation. Except for tests for
hemoglobin (or hematocrit) and, possibly, serum ferritin, it is impractical
to use other laboratory and functional tests to assess nutrient status in
routine prenatal care.
After an in-depth review of dietary intake data for women in the
United States and evidence from clinical, metabolic, and epidemiologic
studies, the subcommittee concluded that iron is the only known nutrient
for which requirements cannot be met reasonably by diet alone. 1b meet
the increased need for iron during the second and third trimesters of
pregnancy, the average woman needs to absorb approximately 3 mg of iron
per day in addition to the amount of iron usually absorbed from food.
Evidence from iron absorption studies indicates that low-dose supplements
(e.g., 30 mg of ferrous iron daily) can provide this amount of extra iron.
To lines of evidence contributed to the conclusion that supplementa
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18
SUMAL4RY
lion with iron is advisable: need for iron is high in relation to usual dietary
supply, and iron-supplemented pregnant women have higher hemoglobin
levels than do unsupplemented women. Iron meets the subcommittee's
criterion that intake is likely to be low enough to limit the production of a
compound hemoglobin-that is essential for body function. Evidence that
iron deficiency adversely affects maternal and fetal health is only suggestive.
Because iron at low doses poses no known dangers to the mother or fetus,
the subcommittee concluded that in populations that commonly have iron
deficiency, the potential benefits of iron supplementation outweigh the risks.
Low-dose iron supplements offer distinct advantages over higher-dose ones:
less potential for undesirable nutrient-nutrient interactions, more efficient
absorption, and less risk of causing gastrointestinal distress.
Pregnant women can meet the physiologic requirements for folate
from diet by following dietary guidelines such as those provided in the
publications listed at the end of this chapter (American Red Cross, 1984;
Corruccini, 1977; DHHS/USDA~arch of Dimes Birth Defects Foundation,
1982; Dimperio, 1988; USDA, 1979, 1989~. Folate deficiency now appears
to be very rare among pregnant women in the United States. The extent to
which the common practice of folate supplementation has contributed to the
rarity of this deficiency is unknown. In the past, particularly during the l950s
and 1960s, folate deficiency was identified in some women in industrialized
nations, including the United States and the United Kingdom. Pending
further research, the subcommittee considers it prudent to supplement the
diet with low amounts of folate if there is any question of adequacy of
intake of this nutrient.
Evidence is not sufficient to conclude that routine supplementation
with other nutrients is warranted, although clearly there are situations re-
quiring special consideration. For example, certain dietary practices that
restrict or prohibit the consumption of an important source of nutrients,
such as avoidance of all animal foods or of vitamin D-fortified milk, increase
the risk of inadequate nutrient intake. In such cases, if diet quality cannot
be improved through better food selection, selective supplementation may
be desirable. There is evidence that women carrying more than one fetus
and those who use cigarettes, alcohol, or illicit drugs have increased re-
quirements for certain nutrients. Furthermore, adolescents and drug users
often follow dietary practices that lead to low intakes of a number of
nutrients.
Because protein is abundant in usual diets in the United States and
because of evidence suggesting possible harm from routine ingestion of
specially formulated high-protein supplements, the use of special pro-
tein powders or formulated high-protein beverages should be discouraged.
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SUMMARY
19
However, there is no contraindication to increased use of food sources
of protein such as milk and flesh foods as part of a well-balanced diet,
especially because these foods are also rich sources of vitamins and minerals.
Although some studies in nonpregnant populations suggest that caf-
feine intake may decrease the availability of certain nutrients such as
calcium, zinc, and iron, there is only inconsistent and fragmentary evidence
that the consumption of coffee or caffeine during pregnancy exerts adverse
effects on the fetus. It nevertheless appears sensible to limit the consump-
tion of caffeine-containing products during pregnancy, although data are
insufficient for setting a specific limit on intake or for recommending nutri-
ent supplementation for women who continue to consume caffeine during
pregnancy.
Special recommendations on the basis of ethnic background alone do
not seem to be warranted at present. There is no evidence of substantial
differences in nutrient requirements among various ethnic groups, but
ethnic differences in food choices and, consequently, in the mean intake
of certain nutrients do exist. For example, because ethnic groups with a
high prevalence of lactose intolerance customarily consume relatively low
amounts of milk, their intakes of calcium and vitamin D deserve special
attention.
The adequacy of calcium and vitamin D intake among pregnant women
under age 25 also deserves special attention, since bone mineral density is
still increasing during that period of life. For older women who become
pregnant, there is no evidence that high calcium intake will Drotect against
later bone loss caused by osteoporosis.
There is some evidence that periconceptional use of multivitamins
or folate may provide some protection against the occurrence of neural
tube defects. Data to support a recommendation to use periconceptional
vitamins for this purpose are not conclusive at this time.
Because of accumulating data that excessive vitamin A consumption
poses a teratogenic risk, supplementation with preformed vitamin A should
be avoided during the first trimester unless there is specific evidence of a
deficiency. Carotene intake need not be restricted.
Clinical Recommendations
Dietary Assessment
Routine assessment of dietary practices is recommended for all preg-
nant women in the United States to allow evaluation of the need for
improved diet or vitamin or mineral supplements.
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20
Iron
SUMMARY
For the general population of pregnant women, supplements of 30
mg of ferrous iron are recommended daily during the second and third
trimesters. This amount of ferrous iron is provided, for example, by
approximately 150 mg of ferrous sulfate, 300 mg of ferrous gluconate, or
100 mg of ferrous fumarate. Administration between meals or at bedtime
on an empty stomach will facilitate iron absorption, but taking ascorbic acid
with supplements containing ferrous iron does not enhance iron absorption.
Folate
Although routine folate supplementation of pregnant women is not
recommended, a supplement of 300 ,ug/day may be given when there are
doubts about the adequacy of dietary folate. Women who ingest fruit,
juices, whole-grain or fortified cereals, and green vegetables infrequently
are likely to have low folate intake.
Multivitamin Mineral Supplements
For pregnant women who do not ordinarily consume an adequate
diet and for those in high-risk categories, such as women carrying more
than one fetus, heavy cigarette smokers, and alcohol and drug abusers,
the subcommittee recommends a daily multivitamin-mineral preparation
containing the following nutrients beginning in the second trimester:
Iron 30 mg Vitamin Be 2 mg
Zinc 15 mg Folate 300 fig
Copper 2 mg Vitamin C 50 mg
Calcium 250 mg Vitamin D 5 ,ug
To promote absorption of these nutrients, the supplement should be
taken between meals or at bedtime.
Nutrient Supplementation in Special Circumstances
As mentioned above, supplementation of other nutrients may be de-
sirable for certain pregnant women in the United States. The following are
the subcommittee's recommendations for those special circumstances.
Vitamin D: 10 ,ug (400 IU) dad) for complete vegetarians (those who
consume no animal products at all) and others with a low intake of vitamin
D-fortified milk. Vitamin D status is a special concern for women at
northern latitudes in winter and for others with minimal exposure to sunlight
and thus reduced synthesis of vitamin D in the skin.
Calcium: 600 mg daily for women under age 25 whose daily dietary
calcium intake is less than 600 ma. 1b enhance absorption and limit
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SUMMARY
21
interaction with iron supplements, the calcium supplement should be taken
at mealtime. There is no evidence that older pregnant women (i.e., those
over age 35) have a special need for supplemental calcium.
Vitamin B`2: 2.0 fig daily for complete vegetarians.
Zinc and copper: When therapeutic levels of iron (>30 mg/day) are
given to treat anemia, supplementation with approximately 15 mg of zinc
and 2 mg of copper is recommended because the iron may interfere with
the absorption and utilization of those trace elements.
Research Recommendations
Surer Needs
· Representative data should be collected on the nutrient status of
pregnant women and their usual dietary and supplement intake, especially
with regard to iron and folate. Pregnant women should be oversampled
in national surveys (e.g., the National Health and Nutrition Examination
Survey and the Continuing Survey of Food Intake of Individuals) to improve
the data base regarding health and usual nutrient intake in relation to age,
income, and ethnic background.
Nutritional Assessment
· Special purpose longitudinal studies should be conducted from be-
fore pregnancy to parturition to relate food and nutrient intake of individ-
ual women to maternal and fetal nutritional status and pregnancy outcome.
Priority should be given to iron; zinc; copper; calcium; magnesium; and
vitamins D, B6, and folate.
· Better practical diagnostic tests should be developed for detecting
deficiencies of the following in pregnancy: folate, zinc, copper, vitamin B6,
calcium, and magnesium.
· Further work is needed to determine the intakes of nutrients by
pregnant teenagers in specific age and economic groups and by women of
different ethnic backgrounds.
· In view of the increasing number of women who bear more than
one fetus, it is important to acquire data on their food and nutrient intakes
in order to develop appropriate nutritional interventions.
· Strategies are needed for investigating the nutritional consequences
of nausea, vomiting, and food cravings and aversions to provide data that
are useful for determining the appropriateness of nutritional interventions
for these conditions.
· Itials should be conducted to assess the effects of nutrient-nutrient
interactions on the absorption and utilization of specific nutrients when
they are included in multinutrient supplements.
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22
SUMMARY
Iron Supplementation
· Studies are needed on the prevention of iron deficiency without
the use of iron supplements. Such methods would include counseling in
the selection of diets to enhance iron absorption. The effectiveness of
iron-fortified foods in preventing iron deficiency requires further study, and
the improvement of fortification methods should be given a high pnorib.
· Randomized, controlled trials are recommended to study the effects
of iron in 15- to 60-mg doses in different formulations that include iron
compounds alone, with folate, and in multinutrient preparations.
Periconcepiu~nal Supplements
Further studies should be conducted to investigate the effectiveness of
routine periconceptional use of vitamins and minerals in the prevention of
birth defects.
Supplementation for High-Risk Groups
Possible benefits of vitamin-mineral supplementation should be stud-
ied for substance abusers, adolescents, and other groups at high risk of
nutritional deficiency.
REFERENCES
American Red Cross. 1984. Better Eating for Better Health: Participant's Guide. I'm
Pregnant: What Should I Eat? American Red Cross, Washington, D.C. 10 pp.
Corruccini, C G. 1977. Nutrition for Pregnancy and Breast Feeding: Eating Right for Your
Baby. Maternal and Child Health Branch, Family Health Services Section, California
Department of Health Services, Sacramento, Calif. 20 pp.
DHHS (Department of Health and Human Services). 1989. Caring for Our Future: the
Content of Prenatal Care. A Report of the Public Health Service Expert Panel on
the Content of Prenatal Care. Public Health Service, U.S. Department of Health and
Human Services, Washington, D.C. 125 pp.
DHHS/USDA/March of Dimes Birth Defects Foundation (Department of Health and Human
Sen~ices/U.S. Department of Agriculture/March of Dimes Birth Defects Foundation).
1982. Food For the Teenager: During and After Pregnancy. DHHS Publ. No.
(HRSA) 82-5106. Public Health Service, U.S. Department of Health and Human
SeIvices, Rockville, Md. 31 pp.
Dimperio, D. 1988. Prenatal Nutrition: Clinical Guidelines for Nurses. March of Dimes
Birth Defects Foundation, White Plains, N.Y. 134 pp.
IOM (Institute of Medicine). 1985. Preventing Low Birthweight. Report of the Committee
to Study the Prevention of Low Birthweight, Division of Health Promotion and
Disease Prevention. National Academy Press, Washington, D.C. 284 pp.
IOM (Institute of Medicine). 1988. Prenatal Care: Reaching Mothers, Reaching Infants.
Report of the Committee to Study Outreach for Prenatal Care, Division of Health
Promotion and Disease Prevention. National Academy Press, Washington, D.C. 254
PP.
Metropolitan Life Insurance Company. 1959. New weight standards for men and women.
Stat. Bull. Metrop. Life Insur. Co. 40:14.
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SUMMARY
23
NRC (National Research Council). 1970. Maternal Nutrition and the Course of Pregnancy.
Report of the Committee on Maternal Nutrition, Food and Nutrition Board. National
Academy of Sciences, Washington, D.C. 241 pp.
USDA (U.S. Department of Agnculture). 1979. Food. Home and Garden Bulletin No. 228.
Science and Education Administration, Food and Nutrition Service, U.S. Department
of Agriculture, Alexandria, Va. 65 pp.
USDA (U.S. Department of Agriculture). 1989. Preparing Foods & Planning Menus Using
the Dietary Guidelines. Home and Garden Bulletin No. 232-8. Human Nutrition
Information Service, U.S. Department of Agriculture. U.S. Government Printing
Office, Washington, D.C. 31 pp.
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Representative terms from entire chapter:
gestational weight
