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OCR for page 37
Historical Trends in Clinical Practice'
Maternal Nutritional Status, and the
Course and Outcome of Pregnancy
Improvement of maternal and fetal health and nutrition has been a
public health goal since the beginning of organized medicine. As knowledge
has accumulated over time, standard clinical practices, attitudes, and be-
liefs regarding prenatal care and nutrition have changed. Furthermore, the
socioeconomic status of the U.S. population has improved along with tech-
nological advancements. Changes in clinical practice and socioeconomic
status undoubtedly have influenced the nutrition and health of women
entering and during their pregnancies, as well as both maternal and fetal
outcomes. The following review of historical trends provides a foundation
for evaluating current standards of practice and relationships between those
standards and gestational weight gain and pregnancy outcome.
TRENDS IN RECOMMENDATIONS
Over the past century, there have been substantial changes in rec-
ommendations made to women about weight gain during pregnancy. In
the sixteenth, seventeenth, and eighteenth centuries, much emphasis was
placed on the maternal diet since the mother was known to be the only
source of nutrients for the fetus (Rosso and Cramoy, 1979~. In the nine-
teenth century, the idea that pregnant women should not overeat became
a recurrent theme. Overeating was believed to be a cause of large babies
and, as a consequence, more difficult labors. In a period when maternal
mortality was extremely high and cesarean deliveries were a desperate al-
ternative, limitation of fetal size by restricting maternal food intakes was an
37
OCR for page 38
38
NUTRITIONAL STATUS AND WEIGHT GAIN
understandable goal. This formed the basis for the first published study of
diet and pregnancy (Prochownick, 1901~. This report showed that restricted
food intake throughout pregnancy reduced the birth weights of males by
approximately 400 g and those of females by 500 g.
In the 1920s in the United States, Davis (1923) reported that maternal
weight gain could be used as an indicator of maternal nutritional status and
that, in turn, maternal nutritional status influenced fetal growth. Mean birth
weight increased with increasing gestational weight gain from approximately
3,100 g with a 7-kg (15-lb) gain to about 3,600 g with a 13.~kg (30-lb) gain.
Following publication of these and successive studies, documentation
of gestational weight gain became an increasingly common clinical practice.
Emphasis was first placed on identification of excessive weight gains rather
than insufficient gains. An excessive weight gain was regarded as a clinical
sign of edema and impending toxemia. Controlling weight gain during
pregnancy was encouraged as a means of preventing toxemia. Salt-free
diets were advocated to control tissue fluid retention (McIlroy and Rodway,
1937), and women were commonly told to restrict their food intake to limit
their total gestational weight gain to no more than 6.8 kg (15 lb) (Bingham,
1932; McIlroy and Rodway, 1937~. Up to World War II, most published
studies of gestational weight gains reported average gains that were low;
several were less than 9.1 kg (20 lb) (Hytten, 1980~.
Hytten and Leitch (1971) analyzed several large studies of gestational
weight gain that were conducted during the 1950s and 1960s (Eastman
and Jackson, 1968; Humphreys, 1954; Singer et al., 1968; Thomson and
Billewicz, 1957) and concluded that an average gain of 12.5 kg (27.5 lb)
is the "physiological normality" in apparently healthy, young, primigravid
women. These data show that weight gain before and during pregnancy had
independent, but additive, effects on birth weight; e.g., a high prepregnancy
weight and a high gestational weight gain resulted in a higher birth weight
than did a low prepregnancy weight with a high gestational weight gain.
In 1970 the Food and Nutrition Board's (FNB's) Committee on Maternal
Nutrition stated that "the desirable average gain is 24 pounds within a
range of 20 to 25 pounds" (NRC, 1970, p. 190~. I\vo years later, the
adhoc Committee on Nutrition of the American College of Obstetricians
and Gynecologists (ACOG) published the same recommendation (Pitkin
et al., 1972), and in 1974, the ACOG Committee on Nutrition repeated
the recommendation in the booklet Nutrition and Maternal Health Care
(Committee on Nutrition, 1974~. The ACOG booklet emphasized that
the pattern of weight gain is equally important, if not more so, than
the total amount of gain and recommended a linear gain from week 13
of gestation through term. These recommendations were supported in
the 1978 booklet Assessment of Maternal Nutnuon published jointly by
ACOG and the American Dietetic Association (Fisk Force on Nutrition,
OCR for page 39
HISTORICAL TRENDS
TABLE 3-1 Weight Gain Recommendations in a Sample of Medical
Textbooks
39
Reference
Recommendation
Clinical Obstetrics
Lull and Kimbrough, 1953
Williams Obstetrics
12th edition
Eastman and Hellman
1961
14th edition
Hellman and Pritchard,
1971
iSth edition
Pritchard and
MacDonald, 1976
16th edition
Pritchard and
MacDonald, 1980
Beck's Obstetrical Practice
9th edition
Taylor, 1971
A total gain of 10.9 kg (24 lb), based on the authors'
own research in which they recorded a 9.S-kg (21-lb)
average linear gain after the first trimester. Weight
gain was related to prematurity and toxemia. The
importance of prepregnancy weight was emphasized,
and a protein intake of 1.S g/kg of body weight was
recommended.
A limitation on weight gain to 11.4 kg (25 lb), at most,
or to 9.1 kg (20 lb), which was considered better.
Restriction of weight gain to 8.2 kg (18 lb) with an
1,800-kcal diet was emphasized. The 1943 RDA of
2,500 kcal/day was suggested.
A gain of 9.1 to 11.4 kg (20 to 25 lb), because it was
associated with the most favorable outcome. Eastman
and Jackson (1968) was cited. The recommendations
of the ACOG Committee on Maternal Nutrition were
summarized, and the 1968 RDAs were listed.
A weight gain of at least 9.1 kg (20 lb) in most cases,
and women should be encouraged to eat as much as
they wish. The 1974 RDAs were listed.
The 1978 ACOG Task Force on Nutritional Status
criteria were reviewed, and the 1980 RDAs were
presented.
A total gain of 9.1 to 11.4 kg (20 to 25 lb), and
instructions were given to gain no more than 0.9 to
1.8 kg (2 to 4 lb) per month. An increase above this
amount was recommended for underweight women,
and obese women were allowed to diet and lose
weight.
1978~. Further emphasis on the weight gain recommendation appeared
in Guidelines for Perinatal Care (AAP/ACOG, 1983) and in Standards for
Obstetric,Gynecolog~c Services (ACOG, 1985~. In 1981, the FNB's Nutrition
Services in Perinatal Care~RC, 1981) presented the following guidelines for
evaluation of weight gain, which were published initially by Pitkin (1977~:
Inadequate gain: Gain of 1 kg or less per month during the second or
third trimesters.
Excessive gain: Gain of 3 kg or more per month (NRC, 1981, p. 12~.
Frequently, but not always, these authoritative recommendations were
incorporated into textbooks, usually at least 1 year after they first ap-
peared (Bible 3-1~. Williams Obstetrics (e.g., Eastman and Hellman, 1961)
OCR for page 40
40
NUTRITIONAL STATUS AND WEIGHT GAIN
a primary reference used in many medical schools, is an example. Edi-
tions published between 1961 and 1980 in general recommended a total
gain of 9.1 to 11.4 kg (20 to 25 lb). The earlier editions recommended
some restriction of gain; the later ones advised a more liberal approach.
The suggestion that weight gain should not be limited and that women
should be allowed to eat as much as they want did not appear until 1976
(Pritchard and MacDonald, 1976~. The FNB's Recommended Dietary A1-
lowances (RDAs) were used as standards for dietary intakes throughout
these editions. Beckons Obstetrical Practice Taylor, 1971) and Clinical Ob-
stetncs (Lull and Kimbrough, 1953) were widely used sources on obstetric
care. The recommendations in these books differed from those in Williams
Obstetrics. Lull and Kimbrough (1953) recommended a total gain of 10.9
kg (24 lb). They also emphasized that prepregnancy weight as well as
gestational weight gain influenced pregnancy outcome. Beck's Obstetrical
Practice (Taylor, 1971) emphasized the existence of a relationship between
prepregnancy weight and gestational weight gain. They suggested that un-
derweight women should be allowed to gain more weight than women of
normal weight and that obese women should be allowed to diet and lose
weight.
The FNB has prepared 10 editions of the RDAs between 1943 and
1989. During that time, energy recommendations for pregnant women
have ranged from 2,200 kcal/day in 1968 to 2,700 kcaVday in 1953 (Table
3-2~. Ironically, the highest energy intakes were recommended during the
1950s, when women were also advised to restrict their weight gain. In the
1960s, the total energy recommendation for pregnant women decreased to
a range of 2,200 to 2,300 kcaVday. In 1974, 2,400 kcal was recommended for
pregnant women. In 1989, the nonpregnant RDA for energy rose another
100 kcal, bringing the total recommended energy intake during pregnancy
to 2,500 kcal.
Recommended gestational weight gains have nearly doubled during
the past 50 years from 6.8 kg (15 lb) in the 1930s to a range of 11.4 to
15.9 kg (25 to 35 lb) in the 1980s. Concurrently, standard clinical practice
changed from restricting to encouraging weight gain during gestation. In
dietetic practice, changes were made from a limited to an unlimited food
intake. The most recent RDAs for energy are consistent with these changes
in clinical practice, but the total amount recommended still falls below that
recommended in the 1950s (NRC, 1953, 1958~.
OCR for page 41
HISTORICAL TRENDS
TABLE 3-2 Recommended Energy Intakes for Pregnant Women Made
by the Food and Nutrition Board (FNB) from 1943 to 1989
~I ~ ~l ~Recommended Energy Intake for
41
Reference
Recommended energy lnlaKe Ior
Nonpregnant Women, kcal/day Pregnant Women
(activity level or age group)
Increment, kcal Total kcal/day
NRC, 1943, 1945 2,100 (sedentary) NRa 2,500
2,500 (moderately active)
3,000 (very active)
NRC, 1948 2,000 (sedentary) NRa 2,400 Sedentary
2,400 (moderately active)
3,000 (very active)
NRC, 1953 2,300 +400 2,700
NRC, 1958 2,300 +300 2,600
NRC, 1964 2,100 +200 2,300
NRC, 1968 2,000 +200 2,200
NRC, 1974 2,100 +300 2,400
NRC, 1980 2,100 (19-22 yr) +300 2,400
2,000 (2~50 yr) 2,300
NRC, 1989 2,200 +300 2,500
a NR = Not reported.
b Recommendations for women in the other two activity groups are calculated by adding
20% to the recommendation for nonpregnant women.
TRENDS IN MATERNAL NUTRITIONAL STATUS AND
CHARACTERISTICS ASSOCIATED WITH OUTCOME
Not only have standards for clinical practice changed in the past 50
years, but there also have been substantial changes in the health status and
the health habits of women who are entering pregnancy.
Maternal Body Size
Maternal weight, height, and weight-for-height ratios are used fre-
quently as indirect measures of nutritional status. The ability to establish
a trend in body size requires serial data from representative subjects from
the same population over time. Changes in maternal body size have not
been studied systematically, but national surveys of representative samples
of U.S. women of reproductive age can be used to identify trends in body
weight, height, and weight-for-height ratios. The weight-for-height ratio
used most frequently in the analysis of these data is the body mass index
(BMI), which is calculated from weight and height (see Chapter 4~. BMI
measurements generally correlate well with more accurate measurements
of body fat content such as body density or total body water (Garrow,
1983~.
Three large national health surveys have been conducted in the United
OCR for page 42
42
NUTRITIONAL STA17JS AND WEIGHT GAIN
TABLE 3-3 Trends in the Heights of U.S. Women Aged 18 to 24 Years
from 1960 to 1980
Years of Study and Height, cm (in.) Percentage of Population by Height
Reference Mean Median <157 cm (<62 in.) <160 cm (<63 in.)
196~1962 162 (63.8) 162 (63.9) 24.6 40.1
NCHS, 1965
1971-1974 163 (64.3) 163 (64.3) 16.6 29.8
Abraham et al., 1979
197~1980 163 (64.3) 164 (64.5) 17.8 29.1
Najjar and
Rowland, 1987
States since 1960: the National Health Examination Survey, Cycle I (HES)
(1960-1962~; the first National Health and Nutrition Examination Survey
(NHANES I) (1971-1974~; and the second National Health and Nutrition
Examination Survey (NHANES II) (1976-1980~. These data show that the
mean height of women between 18 and 24 years of age increased 1.8 cm
(0.7 in.) between the 1960-1962 (NCHS, 1965) and 1971-1974 (Abraham
et al., 1979) surveys; the median height increased 1 cm (0.4 in.) during
the same period (Table 3-3~. Changes in the percentage of women who
were less than 160 cm (63 in.) in height are much more dramatic. In the
1960-1962 survey, 40% of the women surveyed were less than 160 cm tall;
this dropped to 30% in the 1971-1974 survey. During the 1970s, there was
little change in the mean heights of women or in the proportion of short
women.
Using data from these three national surveys, Flegal et al. (1988)
calculated the trends in BMI. The skinfold thicknesses of the women in
these three surveys were also summarized. Data were provided for women
in two age groups (18 to 24 and 25 to 34 years), for blacks and whites, and
for level of education and income. Between the 1960-1962 and 1976-1980
surveys, an increase in body weight of 2.5 to 3.0 kg (5.5 to 6.6 lb) resulted in
a statistically significant increase in BMI for women of both races and for
women under and over age 25. Increases in triceps and subscapular skinfold
thicknesses paralleled the trends in BMI and body weight, suggesting that
much of the change in BMI was due to an increase in body fat.
Using the same data base, Harlan et al. (1988) searched for evidence
of an increase in the prevalence of obesity. They found that the proportion
of white women with BMIs above the 75th percentile for age and sex,
based on the 1959 Metropolitan Life Insurance Standards (Metropolitan
Life Insurance Company, 1959), increased from approximately 22 to 30%
between the 1960-1962 and 1976-1980 suIveys, and that the proportion of
black women above the 75th percentile increased from about 43 to 49%.
OCR for page 43
HISTORICAL TRENDS
43
Thus, during the past two decades, women in the United States have
become taller and heavier. But the increase in body weight was greater
than the increase in height, resulting in an increase in BMI and, therefore,
the prevalence of overweight women of reproductive age. These changes in
maternal body size may influence pregnancy outcomes: infant birth weight
has been correlated with maternal height, weight, and weight-for-height
ratios (Kramer, 1987~.
Age of Menarche
The onset of menstruation is believed to be related to body size
(Frisch, 1980~; i.e., a particular ratio of fat to lean mass and total body
weight is necessary for puberty. Since adult female body size has increased
during the past two decades, the possibility of a lowered age of menarche
was investigated. Earlier menarche could be accompanied by an increased
prevalence of young mothers, which in turn might influence the course and
outcome of pregnancy.
There are some data on the average age at onset from the first half
of the nineteenth century in studies from Scandinavia, Great Britain, and
Germany (Tanner, 1981~. These data suggest that there has been a 3-year
decrease in the average age of menarche from the early 1800s to the mid-
twentieth century. If the decrease is linear, this is equivalent to a decrease
of 3 to 4 months per decade (Frisch, 1984~. However, in four individual
studies published between 1948 and 1976, the average age at menarche
remained at 12.9 years in the United States (Zacharias et al., 1976~.
Maternal Age and Parity
Maternal age and parity are reported to influence the size of the baby
at birth (Kramer, 1987~. In general, primiparous women give birth to
infants who are smaller than those of multiparous women. In some studies,
very young mothers tend to have smaller babies than do older women.
National vital statistics data provide information on the distribution of
births among women of different ages and parities. For this report, data
on the birth weights of singleton infants born in 1960, 1971, 1980, and
1985 were tabulated by race of infant, maternal age, and live birth order.
Maternal age was categorized into four groups: under 18, 18 to 19, 20 to 29,
and 30 and over. Parity was based on live birth order and categorized into
three groups: primiparas, low-parity multiparas, and high-parity multiparas.
High parity was defined as third- or higher-order births to mothers under
age 20 and fourth- or higher-order births to mothers age 20 and over.
There have been changes in the distribution of live births according to
the age of the mother (Figure 3-1), but the 1985 distribution is quite similar
OCR for page 44
44
NUTRTTIONAL STATUS AND WEIGHT GAIN
80
- o
O'
60
.= 40
m
>
._
20
o
80
60
-
m 40
a,
. _
20
o
White Women
1960 1971 1985
Year
Black Women
_ ~
::: 1
1960 1971 1985
Year
i....]
t::::1 < 18yr
~ 18-19 yr
2~29 yr
> 29 yr
FIGURE ~1 Distnbution of live births according to maternal age, by race. Based on
unpublished data from the National Vital Statistics System, computed by the Division of
Analysis from data compiled by the Division of Vital Statistics, National Center for Health
Statistics.
to the 1960 distribution for both whites and blacks. The distribution of
births according to maternal parity changed much more markedly over the
same period. In 1960, approximately 25% of the white births and almost
50% of the black births were to high-parity mothers (Figure 3-2~. By 1985,
high-parity births accounted for only 9% of white and 15% of black births.
This reduction in the prevalence of high-parity births was accompanied by a
sharp increase in the proportion of first births. Between 1960 and 1985, the
OCR for page 45
HISTORICAL TRENDS
45
percentage of births that were first births increased by 55% among white
women and by 80% among black women. There was a relatively large
change in the proportion of first births to mothers aged 30 and over from
2 to 6% of total births among whites and from 1 to 3% of total births
among black;. However, the proportion of total births to women in this
age group was lower than that in 1960.
50
40
30
20
10
o
50
40
- o
o-
In 30
.=
m
a)
._
20
10
o
White Women
1960 1971 1985
Year
Black Women
1960 1971 1985
Year
~ Primiparous ~ Low Parity ~ High Parity
FIGURE 3-2 Distribution of live births according to maternal panty, by race. Based on
unpublished data from the National Vital Statistics System, computed lay the Division of
Analysis from data compiled by the Division of Vital Statistics, National Center for Health
Statistics.
OCR for page 46
46
NUTRITIONAL STATUS AND WEIGHT GAIN
TABLE 3-4 Ethnic Origin of Infants Born in the
United States in 1960a and 1987b
Percentage of
Births
Ethnic Origin
1960
1987
Number of Births
(in thousands)
1960 1987
Whiter 84.6 78.63,6002,992
Black 14.1 16.9602642
American Indian 0.5 1.2644
Chinese 0.1 0.5619
Japanese 0.3 0.31210
All others 0.3 2.515112
a From NCHS, 1962
b From NCHS, 1989a.
c Hispanics were not coded separately prior to 1980. Data from 22
reporting states indicate that there were 289,000 births of Hispanic
origin in 1980 (Ventura, 1983) compared to 405,000 in 1987 (NCHS,
1989a).
Ethnic Origin of Mothers
Maternal ethnic origin has been linked with infant birth weight. In
general, black and Asian mothers give birth to smaller infants than do white
mothers (Kramer, 1987~. Thus, a substantial shift in the ethnic origin of
mothers having babies could influence national data on infant birth weights.
Although the total number of births in the United States decreased
by about 10% between 1960 and 1987, the number of births to nonwhites
other than blacks grew substantially (Table 3-4~. The number of Hispanic
births increased by 40% between 1980 and 1987. (The Hispanic designation
was not on the birth certificate until 1978.)
Smoking Habits of Women of Reproductive Age
Smoking during pregnancy has a detrimental effect on fetal growth
(see the review by Kramer [19873~. Thus, any changes in birth weight
should be compared with changes in maternal smoking habits during the
same period of time.
Between 1965 and 1987, the prevalence of smoking among women
of childbearing age (20 to 44 years of age) decreased from approximately
40 to 30~. Among men in the same age group, the decline was much
greater from 60 to 30% (NCHS, 1989b). Smoking among girls aged 12
tO 17 years also decreased from 24% in 1974 to 15% in 1985 (NCHS,
1989b). Between 1974 and 1985, education replaced gender as the ma-
jor sociodemographic predictor of smoking status. Smoking prevalence
has declined across all educational groups, but the decline has occurred
five times faster among the more educated groups compared with those who
OCR for page 47
HISTORICAL TRENDS
47
are less educated (Pierce et al., 1989~. In 1985, the prevalence of smoking
among people with less than a high school education (34%) was almost
twice that of people with 4 or more years of college education (18%~.
Smoking during pregnancy also decreased during the late 1960s and
the 1970s. Kleinman and Kopstein (1987) analyzed data from two national
samples of live births to married mothers, the 1967 and the 1980 National
Natality Surveys, and showed that the proportion of white married mothers
age 20 and over who smoked decreased from 40 to 25%; the proportion
of pregnant black smokers decreased from 33 to 23% (Figure 3-3~. Un-
fortunately, this decline in smoking was only seen in women over age 20.
The prevalence of smoking among mothers less than age 20 did not change
during this period; approximately 40% of whites and 30% of blacks under
age 20 smoked during their pregnancies in 1967 and 1980.
The higher prevalence of smoking among those with lower levels of
education (Figure 34) may account in part for the substantial portion
of the excess incidence of low-birth-weight infants among these mothers.
Kleinman and Madans (1985) estimated that elimination of smoking would
reduce the incidence of low birth weight by 11% for those with more than
12 years of education and by 35% for those with less than 12 years of
education. In the future, public health programs designed to help women
stop smoking during pregnancy should be directed toward teenagers and
women with less than a high school education.
~ As, 50
o a)
m ~
a) ~
.2.= 40
J ~
._ ~
> a) 30
._ O
oh
c, 0 20
0 ~
5 c,, 10
._ ~
~ '
o
Race and Age Group:
Black (<20 yr)
a White (<20 yr)
White (>20 yr)
1967
Black (>20 yr)
1 980
Year
FIGURE 3-3 Smoking characteristics of married pregnant women, lay race and age. Based
on data from Kleinman and Kopstein (1987~.
OCR for page 52
52
NUTRITIONAL STATUS AND WEIGHT GAIN
3.6
3.5
3.4
-
-
~ 3.3
._
._
m
cry
a)
3.2
3.0
2.9 _
2.8
1 g60
White
3.343 _ _
. _
3.105
1 1 1
3.409 3.421
Black
3.137 3.144
1 970
1980 1 985
Year
FIGURE 3-7 1tends in mean birth weight of live-born singleton infants in the United
States from 1960 through 1985, by race. Based on unpublished data from the National
Vital Statistics System, computed by the Division of Analysis from data compiled by the
Division of Vital Statistics, National Center for Health Statistics.
Birth Weight
U.S. national vital statistics data for 1960 through 1985 provide in-
formation on the trends in mean birth weight as well as the incidence of
low-birth-weight (LBW; <2,500 g), very-low-birth-weight (VLBW; <1,500
g), and high-birth-weight (>4,000 g) infants. For use in this report, data on
the birth weight of singleton, live infants in 1960, 1971, 1980' and 1985 were
tabulated. Between 1960 and 1971, the mean birth weight was constant for
both white and black infants (Figure 3-7), but between 1971 and 1980 it
increased by 60 g for white infants and 30 g for black infants. Between 1980
and 1985, the rate of increase slowed for both whites and blacks. Adjust-
ment of these trends for the changing maternal age and parity distribution
had little effect on the mean birth weights. In 1985, the mean birth weight
of white infants born in the United States averaged 3,421 g and that of
black infants averaged 3,144 g.
Estimates of trends in the mean birth weight of Canadian infants are
based on Statistics Canada data (Arbuckle and Sherman, 1989~. Arbuckle
and Sherman reported that the mean birth weight of Canadian singleton
male infants increased 132 g from 3,325 to 3,457 g between 1972 and
1986; the mean birth weight of female infants increased 135 g from 3,199
to 3,334 g. (Data from vital statistics consistently demonstrate that mean
OCR for page 53
HISTORICAL TRENDS
53
birth weight of males is higher than that of females.) This net change in
the mean birth weight of Canadian infants is nearly double that seen for
white infants in the United States over a similar penod.
Changes in mean birth weight are of some interest, but the extremes
of the birth weight distribution are most important. Figure 3-8 shows the
trends in LBW (<2,500 g) for white and black infants, both full term and
preterm, based on national vital statistics data. From 1960 to 1985, the
incidence of LBW infants declined to 4.755 of white births and to 11%
of black births. The values shown for LBW in 1960 may be lower than
the actual values because of underreporting of LBW during that period
(Kleinman, 1986~.
Adjustment for the changing age-birth order distribution of births
had essentially no effect on these trends. However, there was a large
decline in the percentage of LBW infants born to white women age 30 and
over, especially primiparas. This is probably due in part to the changing
mix of women in this group: during the 1960s, first live births to older
mothers probably included a large proportion of women who had prior
fetal losses. By 1985, a much larger proportion of the women in this
group had intentionally postponed childbirth. The socioeconomic status of
women over age 30 having babies in 1985 probably was higher than that
of women of the same age delivering in 1960. In addition, the medical
a, 20
Black
`' 11.89 <2,500 9 12.2% 11.27% 11.13%
-+
° 10 .
-
.a)
a)
a)
a)
._
~1.88%
._
en
._
m 0.84%
'I 05
5.91
White
c2,5~)0 9 5.74%
Black
< 1,500 9
- _
4.88% 4.73%
1.99% 2 08% 2.28%
I White
1 ~ 1,500 9
0.77% 0.74% 0.75%
1 1 1 1
19&0 1970 1980 1985
Year
FIGURE 38 [lends in low and very low birth weight of live-born singleton infants in
the United States from 1960 through 1985, by race. Based on unpublished data from the
National Vital Statistics System, computed by the Division of Analysis from data compiled
by the Division of Vital Statistics, National Center for Health Statistics.
OCR for page 54
54
15
13
a)
c:
cn
~ o)
~ 0
.~) G
9
m
~ al
~ J
0
Oh
j 7
o
TO
O'
5
NUTRITIONAL STATUS AND WEIGHT GAIN
White
Black
Asian
-
-
Mexican
Puerto Ricar
Cuban
-
-
_
_~ ~
1970 1975 1980
Year
1985 1990
FIGURE 3-9 [lends in low birth weight of live-born singleton infants in the United States
from 1970 through 1987, by race and ethnic background. From NCHS (1990~.
management of pregnancies among older women with chronic illness, such
as hypertension or diabetes, has improved.
Itends in the incidence of VLBW show a sharper divergence by race
(Figure 3-8~. Between 1960 and 1985, the incidence of VLBW white infants
dropped from 0.84 to 0.75% of all births, while the incidence of VLBW
among black infants increased from 1.9 to 2.3%.
The incidence of VLBW among blacks is triple the rate among whites
and the incidence of LBW is double. In an analysis of trends in racial
differences in low birth weight in the United States between 1973 and
1983, Kleinman and Kessel (1987) report that the rate of LBW dropped
by 14% among white women but only 3% among black women. Kleinman
and Kessel (1987) attributed 15% of the decline among the white women
to favorable changes in maternal characteristics, primarily an increase in
educational level. They reported no change in incidence of VLBW infants
among white women, but an increase among black women; 35% of this
increase was attributed to an increase in births to unmarried women.
Published data show national trends in LBW for white, black, American
Indian, and Asian births since 1970 and Hispanic births since 1980 (NCHS,
1990~. These data, which include both single and multiple births, are shown
in Figure 3-9. There was a flattening of the downward trend in LBW for all
ethnic groups during the 1980s. In 1987, LBW infants accounted for about
OCR for page 55
HISTORICAL TRENDS
55
5 to 7% of the births in all groups except Puerto Ricans (9.3%) and blacks
(12.7%~.
An infant may be born small because it was born too early (i.e.,
preterm) or because it experienced growth retardation in utero. Between
1970 and 1980, the incidence of preterm LBW infants declined to the
same degree for both white and black women 7.1% (Kessel et al., 1984~.
The incidence of full-term LBW infants decreased almost three times as
much-20.9%. Consequently, the incidence of preterm LBW infants among
all LBW infants has risen from 51% in 1970 to 56% in 1980. Thus, the
overall decline in LBW has occurred primarily as a result of declines in
full-term LBW infants. Decreased cigarette smoking, improved diets, and
improved utilization of early prenatal care during the 1970s may have
contributed to improved intrauterine growth and, therefore, a reduced rate
of full-term LBW infants.
At the other end of the birth-weight scale, changes in the incidence of
high birth weights for white and black women have been observed (Figure
3-10~. Among whites, the proportion of infants who weighed 4,000 g or
more at birth remained constant during the 1960s but increased by 31%
between 1971 and 1985. For blacks, however, there was a sharp decline
between 1960 and 1971, followed by a 17% increase between 1971 and
1985. In 1985, 12.7% of the white infants and 5.5% of the black infants
weighed 4,000 g or more at birth. An increase in prepregnancy weight
19
14
-
a)
no g
~ o, 9' 3%
- o
cn in
~ s
lo._
~ m
~ a)
m ~5.91%
in,
Ice
._ .
I ~
White
12.21% 12.73%
9.74% _
_
-
4.68% ~
Black
5.2% 5.47%
4 l l l
1960 1970 1980 1985
Year
FIGURE ~10 Itends in high birth weight (4 kg or more) of live-born singleton infants in
the United States from 1960 through 1985, by race. Based on unpublished data from the
National Vital Statistics System, computed by the Division of Analysis from data compiled
by the Division of Vital Statistics, National Center for Health Statistics.
OCR for page 56
56
NUTRITIONAL STATUS AND WEIGHT GAIN
and the prevalence of obesity may contribute to the increase in high-birth-
weight infants. It may also be related to the fact that pregnant women are
now encouraged to let their appetite guide the amount they eat, whereas
in the 1960s, women were advised to restrict their weight gain by limiting
food intake.
TRENDS IN GESTATIONAL WEIGHT GAIN
Mends in gestational weight gain are difficult to determine, because it
has not been monitored in representative samples of the U.S. population
over time. A comparison of mean reported weight gains from studies
with large sample sizes completed during the past 45 years provides some
information on weight gain trends. Data from 11 studies of maternal weight
gain and birth weight completed between 1946 and 1983 are summarized
in Able 3-5. Of the women studied in the 1940s, 1950s, and 1960s, the
reported mean weight gain was 10 kg (22 lb) or less. An exception is
the study by Peckham and Christianson (1971) in which weight gain data
were collected from 1963 to 1965 and the average gain was 11.8 kg (26
lb). This was a study of white, primiparous women who were attending
Kaiser prenatal clinics in northern California. There was a smaller group
of women in this study than in the other studies, and the socioeconomic
status of the women was relatively high, as is characteristic of a health
maintenance organization. Women studied in Boston during World War
II (Beilly and Kurland, 1945) gained as much weight, on average, as did
women from another urban area, Baltimore, about 15 years later (Eastman
and Jackson, 1968~.
After 1970, there appears to be an incremental increase in reported
mean gestational weight gains. All studies conducted after 1970 show a
mean gain of more than 12.5 kg (27 lb). These data were collected after the
1970 FNB report Matemal Nutnuon and the Course of Pregnancy, (NRC,
1970), in which it was recommended that women gain an average of 11
kg (24 lb) during pregnancy. Thus, the upward shift may be related lo a
more liberal attitude regarding weight gain and, therefore, food intake in
the 1970s. Gormican et al. (1980) reported that the mean gain of women
attending their clinics in Madison, Wisconsin, during the last two trimesters
averaged 7.2 kg (16 lb) before 1971 and 11 kg (24 lb) afterward, when clinic
philosophy regarding weight gain was liberalized. In that study the higher
gain after 1971 was associated with a 2-kg (4.4-lb) net increase in maternal
body weight at 4 to 8 weeks postpartum, whereas a small average weight
loss occurred in the women who were given advice to restrict their energy
intake prior to 1971, suggesting that the increased gestational weight gains
were associated with a gain of maternal fat.
In the early 1980s, mean gains of as much as 15 kg (33 lb) were
OCR for page 57
HISTORICAL TRENDS
TABLE 3-5 Gestational Weight Gain and Birth Weights of Full-Term
Deliveries, 1942 through 1983
57
Period ofNumber
Dataof Mean Weight Mean Birth
Reference CollectionSubjects Gain, kg (lb) Weight, g
Prior to 1970
Beilly and Kurland, 1945 1942-1943 979 10.1 (22.3) 3,263
Simpson et al., 1975a 194~1966 26,468 8.9 (19.6) 3,237
Eastman and Jackson, 1968a l9S~1961 11,911 9.4 (20.7) 3,314
Niswander and Jackson, 1974a 1959-1966 16,894 9.8 (21.6) 3,202
Peckham and Christianson, 1971 1963-1965 352b 11.8 (25.9) 3,389
Nyirjesy et al., 1968 196~1966 12 569 9 tic `21 9' NRd
Meyer, 1978 196(}19-61 51,490 10.2 (22.6) NRd
After 1970
Brown et al., 1981 1969-1976 247 12.6 (27.7) 3,234
Taffel, 1986 1980 2,930,000 13.2 (29.1) 3,387
Shepard et al., 1986 198(}1982 4,186 14.9 (32.8) 3,442
Abrams and Laros, 1986 198~1983 1,535e 15.2 (33.4) 3,414
a Data for blacks and whites were originally reported separately but are combined for this
table.
b Includes only white, primiparous women in medium weight group.
c Median (not mean) weight gain.
d NR = Not reported.
e Includes only women of ideal weight for height.
Observed in two studies (Abrams and Laros, 1986; Shepard et al., 1986).
Early returns from the 1988 National Maternal and Infant Health Survey
suggest that there has been a continuing increase in maternal weight gain in
the 1980s. Final results will not be available until 1991 (K Keppel, National
Center for Health Statistics, personal communication, 1989~. Between the
1960s and the 1980s, there was an approximately 50% increase in gestational
weight gain, from about 10 to 15 kg (22 to 33 lb). The change in average
birth weight increased 100 to 150 g. Although the increase in weight gain
was contemporaneous with an increase in birth weight, the change in birth
weight was small, about a 20- to 30-g increase in birth weight for every 1-kg
increase in total weight gain.
SUMMARY
On average, in the early 1980s women gained approximately 3.6 to
4.5 kg (8 to 10 lb) more weight than was reported during studies between
1940 and 1970. Since 1970, there has been a shift away from limiting
weight gain, a decline in the percentage of women who are short, an
increase in the percentage of women who began prenatal care in the first
trimester, and initiation and growth of the WIC program, which provides
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58
NUTRITIONAL STATUS AND WEIGHT GAIN
food supplements or vouchers to eligible low-income, pregnant women.
Each of these changes may have contributed to the increase in average
gestational weight gain.
This upward shift in gestational weight gain occurred simultaneously
with lower infant mortality rates, increased average birth weights, a de-
creased incidence of LBW infants but an increased incidence of VLBW
infants among blacks and little change in the incidence of VLBW white
infants. Most impressive is the increase in high birth weight (>4,000 g)
infants during the 1970s from 9.7 to 12.2% among whites and 4.7 to 5.2%
among blacks.
Several sociodemographic changes occurring in the 1980s suggest that
a decline in gestational weight gain may occur. In the early 1980s, for
example, enrollment for early prenatal care declined, and alcohol and
cocaine use became more prevalent among women of reproductive age.
Potential deterioration of maternal health habits should be kept in mind
as future standards for prenatal care are established. If socioeconomic
barriers make it more difficult for pregnant women to achieve good health
and nutrition, it is even more important that care providers continue to
encourage weight gain and good nutrition.
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Representative terms from entire chapter:
birth weight
