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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
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,
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)
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~.
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
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%.
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
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
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.
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
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~.
48 NUTRITIONAL STATUS AND WEIGHT GAIN Use of Selected Substances Information on the use of alcohol, marijuana, and cocaine during the previous month were collected in national surveys conducted between 1972 and 1988 (NCHS, 1990~. Data are not available for all age and sex groups in each year. In 1976, 58% of the women aged 18 to 25 reported using alcohol in the past month. This increased to 68% in 1979 and declined slightly to 57% in 1988. Data on the use of marijuana by women aged 18 to 25 have been tabulated for the period from 1976 to 1988. In 1976, 19% reported using marijuana in the past month. This increased to 26% in 1979 and fell to 11% in 1988. Data on cocaine use among women between the ages of 18 and 25 years are only available for the years from 1982 to 1988. During this period, the number of women who reported using cocaine in the past month increased by one-third from 4.7 to 6.3~but then declined to 3.0% in 1988. It should be noted, however, that emergency room admissions with mention of cocaine for women aged 18 to 25 quadrupled between 1984 and 1988 (N Kopstein, National Institute on Drug Abuse, personal communication, 1989~. If we assume that the lifestyles of women who became pregnant in 1985 were similar to those of the women in the survey, we can also assume that the prevalence of substance use would be the same, i.e., alcohol, 64%; marijuana, 17%; and cocaine, >6%. There are no specific data on alcohol, marijuana, and cocaine use among pregnant women in the United States. However, studies of selected populations show cocaine use during pregnancy up to 25% (Chasnoff, 1989~. >a cat O ~ 60 m ~ a> .= - < n c] a) > ~ en a) O ~ s 0 ~ , ~ ~ ' 50 40 20 10 o Length of Education: ~ <12yr C: 12yr 13-15 yr 1967 >15yr 1 980 Year FIGURE 3-4 Smoking habits of white married women over age 20, by level of education. Based on data from Kleinman and Kopstein, (1987~.
HISTORICAL TRENDS 49 TRENDS IN USE OF PRENATAL CARE AND FOOD SUPPLEMENTATION PROGRAMS Changes in the availability of prenatal care and food supplementation programs can have a great impact on the general and nutritional health of pregnant women. Poor prenatal care and insufficient food intake both have been associated with poor pregnancy outcomes. Trends in the use of prenatal care since 1969 were recently summarized in the Institute of Medicine report Prenatal Care: Reaching Mothers, Reaching Infants (IOM, 1988~. Steady increases in the percentage of births to mothers who received prenatal care in the first trimester of pregnancy occurred for both whites and blacks between 1969 and 1980. In 1980, about 76% of the babies were born to women who had begun receiving prenatal care in the first trimester. This proportion has remained essentially constant between 1980 and 1987. Among black women, 8.8% of the new mothers had received late or no prenatal care in 1980. By 1987, the prevalence had increased to 11%. Of the white women giving birth, 4.3% and 5.0% received little or no prenatal care in 1980 and 1987, respectively (NCHS, 1990~. Social, economic, and other changes in the 1980s have been offered as explanations for this disturbing trend. These include the increase in unemployment in the early 1980s and the resulting loss of employer-based health insurance and personal income; the increasing proportion of women of childbearing age living in poverty; and the increasing number of employed people with inadequate or no health insurance, along with the continuing erosion of maternity benefits under private health insurance plans. The increasing proportion of births to unmarried women and the growth in the number of households headed by single women may also have contributed to this trend. The Special Supplemental Food Program for Women, Infants, and Children (WIC), administered by the U.S. Department of Agriculture (USDA), has had an increasing impact on the provision of food to dis- advantaged pregnant women in the United States since 1974 (Rush et al., 1988~. Before then, there was distribution of supplemental food to a rel- atively small number of pregnant women through USDA:s Supplemental Food Program. This program provided allotments of canned meat or poul- try, peanut butter or dried beans, egg mix, nonfat dry mild powder, canned fruits or vegetables, canned juice, evaporated milk, and hot or cold cereal. The primary objective of the Supplemental Food Program was distribution of surplus commodity foods to low-income people in general; there was no special attempt to supply foods to pregnant women. In contrast, the WIC program provides nutrition education, counseling, and referrals, in addition to food or vouchers, for a carefully tailored, nutritious food pack
so NUTRITIONAL STATUS AND WEIGHT GAIN 450 400 350 300 250 a, ILL 200 150 100 - 1 1 1 1977 1 980 1985 1 988 Year FIGURE ~5 Estimated WIC participation, 1977 through 1988. "Pregnant" includes women up to 6 weeks post partum. The percentage of all women participants who are pregnant is assumed to be constant at the level of 53.7~o as found in the 1984 Study of WIC Participant and Program Characteristics (Richman et al., 1986~. Based on data from USDA (1988). age to pregnant, low-income women who meet state criteria for nutritional risk. Other priority groups targeted by the WIC program include lactating women and children from infancy up to age 5. The WIC program has reached increasing numbers of pregnant women each year (Figure 3-5~. Estimated average participation per year grew from 9,000 pregnant women in 1974 to approximately 440,000 in 1988 (J. Hirschman, Food and Nutrition Service, USDA, personal communication, 1989), but it still does not serge all those who are eligible. In 1987, 78.1% of pregnant women who were certified to receive food or food instruments (vouchers) took advantage of the program; only the actual participants are included in Figure 3-5. Each month, an average WIC package provides the equivalent of 20.5 quarts of milk, 1.9 pounds of cheese, 2.1 dozen eggs, 259.6 ounces of juice, 33.3 ounces of cereal, and 12 ounces of dried beans, dried peas, or peanut butter. If this food is consumed evenly over a month, this package would provide about 900 to 1,000. kcaVday and 40 to 50 g of protein per day. The effects of the WIC program on maternal weight gain and birth weight are briefly reviewed in Chapter 7. TRENDS IN PREGNANCY OUTCOME The changes in maternal health habits and characteristics noted above could have both a positive and negative impact on infant mortality and birth
HISTORICAL TRENDS 51 weight. The increase in maternal body size, decrease in smoking prevalence, and improved accessibility to supplemental foods would be expected to be associated with an improved outcome, whereas the increased prevalence of late or no prenatal care would be expected to cause poorer outcomes. Given these divergent changes in maternal health characteristics and habits, it is not possible to predict trends in infant mortality rates or birth weights based on these data alone. Infant Mortality Infant mortality is used frequently as an indicator of infant health. Neonatal mortality (deaths occurring during the first 28 days of life) is considered to be related to the course of pregnancy. Between 1950 and 1987, infant mortality rates for all races declined from 29.2 to 10.1 deaths per 1,000 live births (Figure 3-6) (NCHS, 1990~. Infant mortality among black infants was about twice that observed among white infants. After a plateau during the 1950s and early 196Os, infant mortality declined rapidly from 1965 to 1980 for both whites and blacks. The rate of decline slowed during the 1980s, especially among blacks. Most of the improvement in infant mortality was due to reductions in birth weight-specific mortality; relatively little was due to improvement in the birth weight distribution (Buehler et al., 1987~. In other words, through improved neonatal intensive care, deaths among high risk births were reduced. 50 cn ._ a, 30 . _ lo to i- 20 c, cn a) 10 Black All races ~ 1950 1960 1970 1980 Year FIGURE 36 Infant mortality rates in the United States, 1950 through 1987, By race. From NCHS (1990).
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
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.
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
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.
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
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
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. REFERENCES AAP/ACOG (American Academy of Pediatrics/American College of Obstetricians and Gynecologists). 1983. Guidelines for Perinatal Care. American Academy of Pediatrics, Elk Grove, Ill. 288 pp. Abraham, S., CL. Johnson, and M.F. Najjar. 1979. Weight and Height of Adults 18-74 Years of Age, United States, 1971-74. Vital and Health Statistics, Series 11, No. 211. DHEW Publ. No. (PHS) 79-1659. National Center for Health Statistics, Public Health Service, U.S. Department of Health, Education, and Welfare, Hyattsville, Md. 49 pp. Abrams, B.F., and R.K Laros, Jr. 1986. Prepregnangy weight, weight gain, and birth weight. Am. J. Obstet. G:rnecol. 154:503-509. ACOG (American College of Obstetricians and Gynecologists). 1985. Standards for Obstetric-Gynecologic Services, 6th ed. The American College of Obstetricians and Gynecologists, Washington, D.C. 109 pp. Arbuckle, T.E., and GJ. Sherman. 1989. An analysis of birth weight ~y gestational age in Canada. Can. Med. Assoc. J. 140157-165. Beilly, J.S., and I.I. Kurland. 1945. Relationship of maternal weight gain and weight of newborn infant. Am. J. Obstet. Gynecol. 50:202-206. gingham, A W. 1932. The prevention of obstetric complications by diet and exercise. Am. J. Obstet. Gynecol. 23:3844. Brown, J.E., H.N. Jacobson, L^H. Askue, and M.G. Peick. 1981. Influence of pregnancy weight gain on the size of infants born to underweight women. Obstet. Gynecol. 57:13-17. Buehler, J.W., J.C Kleinman, CJ. Hogue, L.T. Strauss, and J.C Smith. 1987. Birth weight-specific infant mortality, United States, 1960 and 1980. Public Health Rep. 102:151-161. Chasnoff, IJ. 1989. Drug use and women: establishing a standard of care. Ann. N.Y. Acad. Sci. 562:208-210. Committee on Nutrition. 1974. Nutrition in Maternal Health Care. American College of Obstetricians and Gynecologists, Washington, D.C. 13 pp.
HISTORICAL TRENDS 59 Davis, C.H. 1923. Weight in pregnancy; its value as a routine test. Am. J. Obstet. Gynecol. 6:575-581. Eastman, NJ., and LM. Hellman. 1961. Williams Obstetrics, 12th ed. Appleton-Century- Crofts, New York. 1230 pp. Eastman, NJ., and E. Jackson. 1968. Weight relationships in pregnancy I. Ibe bearing of maternal weight gain and pre-pregnancy weight on birth weight in full term pregnancies. Obstet. Gynecol. Sure. 23:1003-1025. Flegal, KM., W.R. Harlan, and J.R. Landis. 1988. Secular trends in body mass index and skinfold thickness with socioeconomic factors in young adult women. Am. J. Clin. Nutr. 48:535-543. Frisch, R.E. 1980. Pubertal adipose tissue: is it necessary for normal sexual maturation? Evidence from the rat and human female. Fed. Proc., Fed. Am. Soc. Exp. Biol. 39.2395-2400. Frisch, R.E. 1984. Body fat, puberty end fertility. Biol. Rev. 59:161-188. Garrow, J.S. 1983. Indices of adiposity. Nutr. Abstr. Rev. 53:07-708. Gormican, A, J. Valentine, and E. Satter. 1980. Relationships of maternal weight gain, prepregnancy weight, and infant birthweight. Interaction of weight factors in pregnancy. J. Am. Diet. Assoc. 77:662~67. Harlan, W.R., J.R. Landis, KM. Flegal, OS. Davis, and M.E. Miller. 1988. Secular trends in body mass in the United States, 1960-1980. Am. J. Epidemiol. 128:1065-1074. Hellman, LM., and J.A Pritchard. 1971. Williams Obstetrics, 14th ed. Appleton-Century- Crofts, New York. 1242 pp. Humphreys, R.C. 1954. An analysis of the maternal and foetal weight factors in normal pregnancy. J. Obstet. Gynaecol. Br. Commonw. 61:764-771. Hytten, F.E., and I. Leitch. 1971. The Physiology of Human Pregnancy, 2nd ed. Blackwell Scientific Publications, Oxford. 599 pp. Hytten, F.E. 1980. Weight gain in pregnancy. Pp 193-233 in F. Hytten and G. Chamberlain, eds. Clinical Physiology in Obstetrics, Blackwell Scientific Publications, Oxford. 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. Kessel, S.S., J. Villar, H.W. Berendes, and R.P. Nugent. 1984. The changing pattern of low birth weight in the United States: 1970 to 1980. J. Am. Med. Assoc. 251:1978-1982. Kleinman, J.C 1986. Underreporting of infant deaths: then and now. Am. J. Public Health 76:365-366. Kleinman, J.C., and S.S. Kessel. 1987. Racial differences in low birth weight: trends and risk factors. N. Engl. J. Med. 317:749-753. Kleinman, J.G, and ~ Kopstein. 1987. Smoking during pregnant, 1967-80. Am. J. Public Health 77:823-825. Kleinman, J.C., and J.H. Madans. 1985. The effects of maternal smoking, physical stature, and educational attainment on the incidence of low birth weight. Am. J. Epidemiol. 121:843-855. Kramer, M.S. 1987. Determinants of low birth weight: methodological assessment and meta-analysis. Bull. W.H.O. 65:663-737. Lull, C.B., and R.A. Kimbrough, eds. 1953. Clinical Obstetrics. Lippincott, Philadelphia. 732 pp. McIlroy, A.L., and H.E. Rodway. 1937. Weight-changes during and after pregnancy with special reference to early diagnosis of toxaemia. J. Obstet. Gynaecol. Br. Empire 44:221-244. Metropolitan Life Insurance Company. 1959. New weight standards for men and women. Stat. Bull. Metrop. Life Insur. Co. 40:1-4. Meyer, M.B. 1978. How does maternal smoking affect birth weight and maternal weight gain? Evidence from the Ontario Perinatal Mortality Study. Am. J. Obstet. Gynecol. 131:888-893.
60 NUTRITIONAL STATUS AND WEIGHT GAIN Najjar, M.F., and M. Rowland. 1987. Anthropometric Reference Data and Prevalence of Overweight, United States, 1976-80. Vital and Health Statistics, Series 11, No. 238. DHHS Publ. No. (PHS) 877-1688. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services, Hyattsville, Md. 73 pp. NCHS (National Center for Health Statistics). 1962. Vital Statistics of the United States, 1960. Vol. I Natality. National Center for Health Statistics, Public Health Service, U.S. Department of Health, Education, and Welfare, Washington, D.C. (various pagings). NCHS (National Center for Health Statistics). 1965. Weight, Height, and Selected Body Dimensions of Adults, United States 1960-1962. Vital and Health Statistics, Series 11, No. 8. (PHS) Publ. No. 1000. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services. Hyattsville, Md. 44 pp. NCHS (National Center for Health Statistics). 1989a. Advance report of final nasality statistics, 1987. Mon. Vital Stat. Rep. 38:148. NCHS (National Center for Health Statistics). 1989b. Health United States 1988. DHHS Publ. No. (PHS) 89-1232. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services. Hyattsville, Md. 208 pp. NCHS (National Center for Health Statistics). 1990. Health United States 1989. DHHS Publ. No. (PHS) 90 1232. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services, Hyattsville, Md. 291 pp. Niswander. K.. and E.C: Jackson 1974 Physical characteristics of the gravida and their association with birth weight and perinatal death. Am. J. Obstet. Gynecol. 119:306-313. NRC (National Research Council). 1943. Recommended Dietary Allowances. Report of the Food and Nutrition Board. Reprint and Circular Series No. 115. National Academy of Sciences, Washington, D.C. 6 pp. NRC (National Research Council). 1945. Recommended Dietary Allowances, revised 1945. Report of the Food and Nutrition Board. Reprint and Circular Series No. 122. National Academy of Sciences, Washington, D.C 18 pp. NRC (National Research Council). 1948. Recommended Dietary Allowances, revised 1948. Report of the Food and Nutrition Board. Repnnt and Circular Series No. 129. National Academy of Sciences, Washington, D.C. 31 pp. NRC (National Research Council). 1953. Recommended Dietary Allowances, revised 1953. Report of the Food and Nutrition Board. Publication 302. National Academy of Sciences, Washington, D.C. 36 pp. NRC (National Research Council). 1958. Recommended Dietary Allowances, revised 1958. Report of the Food and Nutrition Board. Publication 589. National Academy of Sciences, Washington, D.C. 36 pp. NRC (National Research Council). 1964. Recommended Dietary Allowances, 6th revised ed. Report of the Food and Nutrition Board. Publication 1146. National Academy of Sciences, Washington, D.C. 59 pp. NRC (National Research Council). 1968. Recommended Dietary Allowances, 7th revised ed. Report of the Food and Nutrition Board. Publication 1694. National Academy of Sciences, Washington, D.C. 101 pp. 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. NRC (National Research Council). 1974. Recommended Dietary Allowances, 8th ed. Report of the Committee on Dietary Allowances, Committee on Interpretation of the Recommended Dietary Allowances, Food and Nutrition Board. National Academy of Sciences, Washington, D.C 128 pp. NRC (National Research Council). 1980. Recommended Dietary Allowances, 9th ed. Report of the Committee on Dietary Allowances, Food and Nutrition Board, Division of Biological Sciences, Assembly of Life Sciences. National Academy Press, Washington, D.C. 185 pp. NRC (National Research Council). 1981. Nutrition Services in Perinatal Care. Report of the Committee on Nutrition of the Mother and Preschool Child, Food and Nutrition Board, Assembly of Life Sciences. National Academy Press, Washington, D.C. 72 pp. 7 ,
HISTORICAL TRENDS 61 NRC (National Research Council). 1989. Recommended Dietary Allowances, 10th ed. Report of the Subcommittee on the Tenth Edition of the RDAs, Food and Nutrition Board, Commission on Life Sciences. National Academy Press, Washington, D.C. 284 pp. Nyirjesy, I., W.M. Lonergan, and J.J. Kane. 1968. Clinical significance of total weight gain in pregnancy. I. Pnmipara. Obstet. Gynecol. 32:391-396. Peckham, OH., and R.E. Christianson. 1971. The relationship between prepregnancy weight and certain obstetric factors. Am. J. Obstet. Gynecol. 111:1-7. Pierce, J.P., M.C. Fore, T.E. Novotny, E.J. Hatziandreu, and R.M. Davis. 1989. Trends in cigarette smoking in the United States: educational differences are increasing. J. Am. Med. Assoc. 261:56~0. Pitkin, R.M. 1977. Obstetrics and gynecology. Pp. 407-421 in H.A. Schneider, C.E. Anderson, and D.B. Coumin, eds. Nutritional Support of Medical Practice. Harper & Row, New York. Pitkin, R.M., H.A. Kaminetzky, M. Newton, and J.A. Pritchard. 1972. Maternal nutrition: a selective review of clinical topics. J. Obstet. Gynecol. 40:773-785. Pritchard, J.A., and P.C. MacDonald. 1976. Williams Obstetrics, 15th ed. Appleton- Centu~y-Crofts, New York. 1003 pp. Pritchard, J.A., and P.C. MacDonald. 1980. Williams Obstetrics, 16th ed. Appleton- Centu~y-Crofts, New York. 1179 pp. Prochownick, L 1901. Ueber Ernahrungscuren in der Schwange~chaft. Ther. Monatsh. 15:446~63. Richman, Lo, ~ Hildlebaugh, Lo Ku, N. McMahon-Cox, C.M. Dayton, and N. Goodrich. 1986. Study of WIC Participant and Program Characteristics. Office of Analysis and evaluation, Food and Nutrition Service, U.S. Department of Agriculture, Alexandria, Va. 179 pp. Rosso, P., and C Cramoy. 1979. Nutrition and pregnancy. Pp. 133-228 in M. Schick, ed. Human Nutrition: A Comprehensive Treatise, Vol. 1. Nutrition: Pre- and Postnatal Development. Plenum Press, New York. Rush, D., D.G. Horvitz, W.B. Seaver, J.M. Alvir, G.C. Garbowski, J. Leighton, N.L. Sloan, S.S. Johnson, R.A. Kulka, and D.S. Shanklin. 1988. Ibe National WIC Evaluation: evaluation of the Special Supplemental Food Program for Women, Infants, and Children. I. Background and Introduction. Am. J. Clin. Nutr. 48:389-393. Shepard, MJ., K.G. Hellenbrand, and M.B. Bracken. 1986. Proportional weight gain and complications of pregnancy, labor, and delivery in healthy women of normal prepregnant stature. Am. J. Obstet. Gynecol. 155:947-954. Simpson, J.W., R.W. Lawless, and AC. Mitchell. 1975. Responsibility of the obstetrician to the fetus. II. Influence of prepregnancy weight and pregnancy weight gain on birthweight. Obstet. Gynecol. 45:481487. Singer, J.E., M. Westphal, and K. Niswander. 1968. Relationship of weight gain during pregnancy to birth weight and infant growth and development in the first year of life: a report from the Collaborative Study of Cerebral Palsy. Obstet. Gynecol. 31:417-423. Taffel, S.M. 1986. Maternal Weight Gain and the Outcome of Pregnancy: United States, 1980. Vital and Health Statistics, Series 21, No. 44. DHHS Publ. No. (PHS) 86-1922. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services, Hyattsville, Md. 25 pp. I5nner, J.M. 1981. Growth and maturation during adolescence. Nutr. Rev. 39:43-55. Task Force on Nutrition. 1978. Assessment of Maternal Nutrition. The American Dietetic Association and The American College of Obstetricians and Gynecologists, Washington, D.C. 25 pp. Taylor, E.S. 1971. Beck's Obstetrical Practice, 9th ed. Williams & Wilkins, Baltimore, Md. 665 pp. Thomson, A.M., and W.Z. Billewicz. 1957. Clinical significance of weight trends during pregnancy. Br. Med. J. 1:24~247. USDA (U.S. Department of Agriculture). 1988. Annual Historical Review of ENS Programs: Fiscal Year 1988. Food and Nutrition Service, U.S. Department of Agriculture, Alexandna, Va. 32 pp.
62 NUTRITIONAL STATUS AND WEIGHT GAIN Ventura, SJ. 1983. Births of Hispanic parentage, 1980. Mon. Vital Stat. Rep. 32:1-18. Zacharias, L, W.M. Rand, and RJ. Wurtman. 1976. A prospective study of sexual development and growth in American girls: the statistics of menarche. Obstet. Gynecol. Sum. 31:325-337.