Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 1
Weight Gain During Pregnancy: Reexaming the Guidelines Summary Since 1990, the last time the Institute of Medicine (IOM) released guidelines for weight gain during pregnancy, many key aspects of the health of women of childbearing age have changed. This population now includes a higher proportion of women from racial/ethnic subgroups, and prepregnancy body mass index (BMI) and gestational weight gain (GWG) have increased among all population subgroups. Moreover, high rates of overweight and obesity are common in the population subgroups that are at risk for poor maternal and child health outcomes. Finally, women are also becoming pregnant at an older age and, as a result, are entering pregnancy more commonly with chronic conditions such as hypertension or diabetes, which put them at risk for pregnancy complications and may lead to increased morbidity during their post-pregnancy years. These and other factors suggested a need to reexamine the IOM (1990) guidelines for weight gain during pregnancy and to consider whether revision might be warranted. In response to these concerns, sponsors1 asked the Food and Nutrition 1 Sponsors include U.S. Department of Health and Human Services Health Resources and Services Administration; Centers for Disease Control and Prevention Division of Nutrition and Physical Activity and Obesity; National Institutes of Health Eunice Kennedy Shriver National Institute of Child Health and Human Development; National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases; U.S. Department of Health and Human Services Office on Women’s Health; U.S. Department of Health and Human Services Office of Disease Prevention and Health Promotion; March of Dimes; with additional support from U.S. Department of Health and Human Services Office of Minority Health and the National Minority AIDS Council.
OCR for page 2
Weight Gain During Pregnancy: Reexaming the Guidelines Board of the IOM and the Board on Children, Youth, and Families in the Division of Behavioral and Social Sciences and Education of the National Research Council to review the IOM (1990) recommendations for weight gain during pregnancy. Specifically, the committee was asked to review evidence on relationships between weight gain patterns before, during, and after pregnancy and maternal and child health outcomes; consider factors within a life-stage framework associated with outcomes such as lactation performance, postpartum weight retention, and cardiovascular and other chronic diseases; and recommend revisions to existing guidelines where necessary. Finally, the committee was asked to recommend ways to encourage the adoption of the weight gain guidelines through consumer education, strategies to assist practitioners, and public health strategies. GUIDELINES FOR WEIGHT GAIN DURING PREGNANCY The new guidelines for GWG that are shown in Table S-1 are formulated as a range for each category of prepregnancy BMI. This approach reflects the imprecision of the estimates on which the recommendations are based, the reality that good outcomes are achieved within a range of weight gains, and the many additional factors that may need to be considered for an individual woman. It is important to note that these guidelines are intended for use among women in the United States. They may be applicable to women in other developed countries. However, they are not intended for use in areas of the world where women are substantially shorter or thinner than American women or where adequate obstetric services are unavailable. The new guidelines differ from those issued in 1990 in two ways. First, they are based on the World Health Organization (WHO) cutoff points for the BMI categories instead of the previous ones, which were based on TABLE S-1 New Recommendations for Total and Rate of Weight Gain During Pregnancy, by Prepregnancy BMI Prepregnancy BMI Total Weight Gain Rates of Weight Gain* 2nd and 3rd Trimester Range in kg Range in lbs Mean (range) in kg/week Mean (range) in lbs/week Underweight (< 18.5 kg/m2) 12.5-18 28-40 0.51 (0.44-0.58) 1 (1-1.3) Normal weight (18.5-24.9 kg/m2) 11.5-16 25-35 0.42 (0.35-0.50) 1 (0.8-1) Overweight (25.0-29.9 kg/m2) 7-11.5 15-25 0.28 (0.23-0.33) 0.6 (0.5-0.7) Obese (≥ 30.0 kg/m2) 5-9 11-20 0.22 (0.17-0.27) 0.5 (0.4-0.6) * Calculations assume a 0.5-2 kg (1.1-4.4 lbs) weight gain in the first trimester (based on Siega-Riz et al., 1994; Abrams et al., 1995; Carmichael et al., 1997).
OCR for page 3
Weight Gain During Pregnancy: Reexaming the Guidelines categories derived from the Metropolitan Life Insurance tables. Second, and more importantly, the new guidelines include a specific, relatively narrow range of recommended gain for obese women. These new guidelines should be considered in the context of data on women’s reported GWG. Data from several large groups of women indicate that the mean gains of underweight women fall within the new guidelines, but some normal weight women may exceed these new guidelines and a majority of overweight or obese women will likely exceed them. These data provide a strong reason to assume that interventions will be needed to assist women, particularly those who are overweight or obese at the time of conception, in meeting the guidelines. These interventions may need to occur at both the individual and community levels and may need to include components related to both improved dietary intake and increased physical activity. The committee intends that the guidelines shown in Table S-1 be used in concert with good clinical judgment as well as a discussion between the woman and her care provider about diet and exercise. If a woman’s GWG is not within the proposed guidelines, clinicians should consider other relevant clinical evidence, modifiable factors that might be causing excessive or inadequate gain, and information on the nature of excess GWG (e.g., fat or edema) as well as both the adequacy and consistency of fetal growth before suggesting that a woman modify her pattern of weight gain. Special Populations Women of Short Stature The IOM (1990) report recommended that women of short stature (< 157 cm) gain at the lower end of the range for their prepregnant BMI. The committee was unable to identify evidence sufficient to continue to support a modification of GWG guidelines for women of short stature. Although women of short stature had an increased risk of emergency cesarean delivery, this risk was not modified by GWG. Women of short stature did not have an increased risk of having a small-for-gestational age (SGA) or large-for-gestational age (LGA) infant or of excessive postpartum weight retention over taller women. Pregnant Adolescents Evidence available since the IOM (1990) report is also insufficient to continue to support a modification of the GWG guidelines for adolescents (< 20 years old) during pregnancy. The committee also determined that prepregnancy BMI could be adequately categorized in adolescents by using
OCR for page 4
Weight Gain During Pregnancy: Reexaming the Guidelines the WHO cutoff points for adults, in part because of the impracticality of using pediatric growth charts in obstetric practices. Adolescents who follow adult BMI cutoff points will likely be categorized in a lighter group and thus advised to gain more; however, younger adolescents often need to gain more to improve birth outcomes. Racial or Ethnic Groups Although an increasing proportion of pregnant U.S. women are members of racial or ethnic minority groups, the limited data available to the committee from commissioned analyses suggested that membership in one of these groups did not modify the association between GWG and the outcome of pregnancy. As a result, the committee concluded that its recommendations should be generally applicable to the various racial or ethnic subgroups that make up the American population, although additional research is needed to confirm this approach. Women with Multiple Fetuses Recent data suggest that the weight gain of women with twins who have good outcomes varies with prepregnancy BMI as is clearly the case for women with singleton fetuses. Inasmuch as the committee was unable to conduct the same kind of analysis for women with twins as it did for women with singletons, the committee offers the following provisional guidelines: normal weight women should gain 17-25 kg (37-54 pounds), overweight women, 14-23 kg (31-50 pounds), and obese women, 11-19 kg (25-42 pounds) at term. Insufficient information was available with which to develop even a provisional guideline for underweight women with multiple fetuses. These provisional guidelines reflect the interquartile (25th to 75th percentiles) range of cumulative weight gain among women who delivered their twins, who weighed ≥ 2,500 g on average, at 37-42 weeks of gestation. DEVELOPMENT OF THE GUIDELINES FOR WEIGHT GAIN DURING PREGNANCY The committee worked from the perspectives that the reproductive cycle begins before conception and continues through the first year postpartum and that maternal weight status throughout the entire cycle affects both the mother and her child. To inform its review of the literature and to guide the organization of its report, the committee reevaluated the conceptual framework that guided the development of the IOM (1990) report.
OCR for page 5
Weight Gain During Pregnancy: Reexaming the Guidelines To account for advances in our scientific understanding of the determinants and consequences of GWG, the committee developed a modified conceptual framework (Figure S-1). However, it retained the same scientific approach and epidemiologic conventions used previously and discussed in detail in the IOM (1990) report. The committee began its work by considering appropriate BMI cutoff points and describing trends over time in maternal prepregnancy BMI and GWG among American women. In addition, data were sought on both the determinants and consequences of GWG. The search for such data revealed major gaps in data collection and analysis. Key Finding S-1: The WHO cutoff points for categorizing BMI have been widely adopted and should be used for categorizing prepregnancy BMI as well. Key Finding S-2: Currently available data sources are inadequate for studying national trends in GWG, or postpartum weight, or their determinants. Action Recommendation S-1: The committee recommends that the Department of Health and Human Services conduct routine surveillance of GWG and postpartum weight retention on a nationally representative sample of women and report the results by prepregnancy BMI (including all classes of obesity), age, racial/ethnic group, and socioeconomic status. Action Recommendation S-2: The committee recommends that all states adopt the revised version of the birth certificate, which includes fields for maternal prepregnancy weight, height, weight at delivery, and gestational age at the last measured weight. In addition, all states should strive for 100 percent completion of these fields on birth certificates and collaborate to share data, thereby allowing a complete national picture as well as regional snapshots. Research Recommendation S-1: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct studies in large and diverse populations of women to understand how dietary intake, physical activity, dieting practices, food insecurity and, more broadly, the social, cultural, and environmental context affect GWG. In developing its recommendations, the committee identified a set of consequences for the short- or long-term health of the mother and the child that are potentially causally related to GWG. These consequences included those evaluated in a systematic review of outcomes of maternal weight gain prepared for the Agency for Healthcare Research and Quality (AHRQ) as well as others based on data from the literature outside the time window considered in that report. To address conflicts and gaps within the available literature, the committee commissioned four additional analyses from
OCR for page 6
Weight Gain During Pregnancy: Reexaming the Guidelines FIGURE S-1 Schematic summary of potential determinants and consequences for gestational weight gain. SOURCE: Modified from IOM, 1990.
OCR for page 7
Weight Gain During Pregnancy: Reexaming the Guidelines existing databases. The committee considered the results from these commissioned analyses in conjunction with evidence from published scientific literature. Postpartum weight retention, cesarean delivery, gestational diabetes mellitus, and pregnancy-induced hypertension or preeclampsia emerged from this process as being the most important maternal health outcomes. The committee removed preeclampsia and gestational diabetes mellitus from consideration because of the lack of sufficient evidence that GWG was a cause of these conditions. Postpartum weight retention and, in particular, unscheduled primary cesarean delivery were retained for further consideration. Measures of size at birth (e.g., SGA and LGA), preterm birth, and childhood obesity emerged from this process as being the most important infant health outcomes. The committee recognized that both SGA and LGA, when defined as < 10th percentile and > 90th percentile of weight-for-gestational age, respectively, represent a mix of individuals who are appropriately or inappropriately small or large. In addition, the committee recognized that being SGA was likely to be associated with deleterious outcomes for the infant but not the mother, while being LGA was likely to be associated with consequences for both the infant and the mother (e.g., cesarean delivery). Key Finding S-3: Evidence from the scientific literature is remarkably clear that prepregnancy BMI is an independent predictor of many adverse outcomes of pregnancy. As a result women should enter pregnancy with a BMI in the normal weight category. Key Finding S-4: Although a record-high proportion of American women of childbearing age have BMI values in obesity classes II and III, available evidence is insufficient to develop more specific recommendations for GWG among these women. Research Recommendation S-2: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct studies in all classes of obese women, stratified by the severity of obesity, on the determinants and impact of GWG, pattern of weight gain, and its composition on maternal and child outcomes. Key Finding S-5: There are only limited data available with which to link GWG to health outcomes of mothers and children that occur after the neonatal period. Research Recommendation S-3: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct studies on the eating behaviors, patterns of dietary intake and physical activity, and metabolic profiles of pregnant women, especially obese women, who experience low gain or weight loss
OCR for page 8
Weight Gain During Pregnancy: Reexaming the Guidelines during pregnancy. In addition, the committee recommends that researchers should conduct studies on the effects of weight loss or low GWG, including periods of prolonged fasting and the development of ketonuria/ketonemia during gestation, on growth and on development, and long-term neuro-cognitive function in the offspring. Research Recommendation S-4: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct observational and experimental studies on the association between GWG and (a) glucose abnormalities and gestational hypertensive disorders that take into account the temporality of the diagnosis of the outcome and (b) the development of glucose intolerance, hypertension, and other cardiovascular risk factors as well as mental health and cancer later in a woman’s life. Research Recommendation S-5: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct studies that (a) explore mechanisms, including epigenetic mechanisms, that underlie effects of GWG on maternal and child outcomes and (b) address the extent to which optimal GWG differs not only by maternal prepregnancy BMI but also by other factors such as age (especially among adolescents), parity, racial/ethnic group, socioeconomic status, co-morbidities, and maternal/paternal/fetal genotype. Research Recommendation S-6: The committee recommends that the National Institutes of Health and other relevant agencies should provide support to researchers to conduct observational and experimental studies to assess the impact of variation in GWG on a range of child outcomes, including duration of gestation and weight and body composition at birth, and neurodevelopment, obesity and related outcomes, and asthma later in childhood. Based on the available published literature as well as the reports of its consultants, the committee ascertained the GWG value or range of values associated with lowest prevalence of the outcomes of greatest interest. When weighting the trade-off among these outcomes, the committee considered, within each category of prepregnant BMI (a) the incidence or prevalence of each of these outcomes, (b) whether the outcomes were permanent (e.g., neurocognitive deficits) or potentially modifiable (e.g., postpartum weight retention), and (c) the quality of the available data. The committee compared the resulting ranges with those developed in the quantitative risk analysis conducted by its consultants. Finally, the committee considered how its possible recommendations might be accepted and used by clinicians and women. Research Recommendation S-7: To permit the development of improved recommendations for GWG in the future, the committee recommends that the National Institutes of Health and other relevant agencies
OCR for page 9
Weight Gain During Pregnancy: Reexaming the Guidelines should provide support to researchers to (a) conduct studies to assess utilities (values) associated with short- and long-term health outcomes associated with GWG for both mother and child and (b) include these values in studies that employ decision analytic frameworks to estimate optimal GWG according to category of maternal prepregnancy BMI and other subgroups. APPROACHES TO ACHIEVING RECOMMENDED WEIGHT GAIN DURING PREGNANCY To meet the recommendations of this report fully, two different challenges must be met. First, a higher proportion of American women should conceive at a weight within the range of normal BMI values. Meeting this first challenge requires preconceptional counseling and for many women some weight loss. Such counseling may need to include additional contraceptive services as well as services directed toward helping women to improve the quality of their diets and increase their physical activity. Preconception counseling is an integral part of the recommendations from the Centers for Disease Control and Prevention (Johnson et al., 2006). Practical guidelines for preconceptional care are provided in Nutrition During Pregnancy and Lactation: An Implementation Guide (IOM, 1992). The need to meet this challenge reinforces the importance of preconceptional counseling as the cornerstone for achieving optimal outcomes of pregnancy and improved health for mothers and their children. Action Recommendation S-3: The committee recommends that appropriate federal, state, and local agencies as well as health care providers should inform women of the importance of conceiving at a normal BMI and that all those who provide health care or related services to women of childbearing age should include preconceptional counseling in their care. Second, a higher proportion of American women should limit their GWG to the range specified in these guidelines for their prepregnant BMI. Meeting this second challenge requires a different set of services. The first step in assisting women to gain within these guidelines is letting them know that they exist, which will require educating their health care providers as well as the women themselves. Action Recommendation S-4: The committee recommends that relevant federal agencies, private voluntary organizations, and medical and public health organizations adopt these new guidelines for GWG and publicize them to their members and also to women of childbearing age. Individualized attention is called for in the IOM (1990) guidelines and was an element in all of the interventions that have been successful in helping women to gain within their target range. Guidelines on providing such care are provided in Nutrition During Pregnancy and Lactation: An
OCR for page 10
Weight Gain During Pregnancy: Reexaming the Guidelines Implementation Guide (IOM, 1992). The increase in prevalence of obesity that has occurred since this report was written suggests that this recommendation has only become more important. In offering women individualized attention, a number of kinds of services could be considered. Health care providers should chart women’s weight gain and share the results with them so that they become aware of their progress toward their weight-gain goal. To assist health care providers in doing this, the committee has prepared charts that could be used as a basis for this discussion with the pregnant woman. These charts are meant to be used as part of an assessment of the progress of pregnancy and a woman’s weight gain, looking beyond the gain from one visit to the next and toward the overall pattern of weight gain. In addition, women should be provided with individualized advice about both diet and physical activity (ACOG, 2002). This may require referral to a dietitian as well as other appropriately qualified individuals, such as those who specialize in helping women to increase their physical activity. These services may need to continue into the postpartum period to give women the maximum support to return to their prepregnant weight within the first year and, thus, to have a better chance of returning to a normal BMI value at the time of a subsequent conception. Individualized attention is likely to be necessary but not sufficient to enable most women to gain within the new guidelines. Family- and community-level factors must also be addressed if women are to succeed in gaining within these guidelines. Further research on these kinds of multi-level, ecological determinants of GWG is needed to guide the development of comprehensive and effective implementation strategies to achieve these guidelines. In addition, special attention should be given to low-income and minority women, who are at risk of being overweight or obese at the time of conception, consuming diets of lower nutritional value, and of performing less recreational physical activity. Action Recommendation S-5: To assist women to gain within the guidelines, the committee recommends that those who provide prenatal care to women should offer them counseling, such as guidance on dietary intake and physical activity, that is tailored to their life circumstances. Research Recommendation S-8: The committee recommends that the Department of Health and Human Services should provide funding for research to aid providers and communities in assisting women to meet these guidelines, especially low-income and minority women. The committee also recommends that the Department of Health and Human Services should provide funding for research to examine the cost-effectiveness (in terms of maternal and offspring outcomes) of interventions designed to assist women in meeting these guidelines.
OCR for page 11
Weight Gain During Pregnancy: Reexaming the Guidelines CONCLUDING REMARKS Although the guidelines developed as part of this committee process are not dramatically different from those published previously (IOM, 1990), fully implementing them would represent a radical change in the care provided to women of childbearing age. In particular, the committee recognizes that full implementation of these guidelines would mean: Offering preconceptional services, such as counseling on diet and physical activity as well as access to contraception, to all overweight or obese women to help them reach a healthy weight before conceiving. This may reduce their obstetric risk and normalize infant birth weight as well as improve their long-term health. Offering services, such as counseling on diet and physical activity, to all pregnant women to help them achieve the guidelines on GWG contained in this report. This may also reduce their obstetric risk, reduce postpartum weight retention, improve their long-term health, normalize infant birth weight, and offer an additional tool to help to reduce childhood obesity. Offering services, such as counseling on diet and physical activity, to all postpartum women. This may help them to eliminate postpartum weight retention and, thus, to be able to conceive again at a healthy weight as well as improve their long-term health. The increase in overweight and obesity among American women of childbearing age and failure of many pregnant women to gain within the IOM (1990) guidelines alone justify this radical change in care as women clearly require assistance to achieve the recommendations in this report in the current environment. However, the reduction in future health problems among both women and their children that could possibly be achieved by meeting the guidelines in this report provide additional justification for the committee’s recommendations. These new guidelines are based on observational data, which consistently show that women who gained within the IOM (1990) guidelines experienced better outcomes of pregnancy than those who did not (see Chapters 5 and 6). Nonetheless, these new guidelines require validation from experimental studies. To be useful, however, such validation through intervention studies must have adequate statistical power not only to determine if a given intervention helps women to gain within the recommended range but also to determine if doing so improves their outcomes. In the future, it will be important to reexamine the trade-offs between women and their children in pregnancy outcomes related to prepregnancy BMI as well as GWG, and also to be able to estimate the cost-effectiveness of interventions designed to help women meet these recommendations.
OCR for page 12
Weight Gain During Pregnancy: Reexaming the Guidelines REFERENCES Abrams B., S. Carmichael and S. Selvin. 1995. Factors associated with the pattern of maternal weight gain during pregnancy. Obstetrics and Gynecology 86(2): 170-176. ACOG (American College of Obstetricians and Gynecologists). 2002. ACOG committee opinion. Exercise during pregnancy and the postpartum period. Number 267, January 2002. American College of Obstetricians and Gynecologists. International Journal of Gynaecology and Obstetrics 77(1): 79-81. Carmichael S., B. Abrams and S. Selvin. 1997. The pattern of maternal weight gain in women with good pregnancy outcomes. American Journal of Public Health 87(12): 1984-1988. IOM (Institute of Medicine). 1990. Nutrition During Pregnancy. Washington, DC: National Academy Press. IOM. 1992. Nutrition During Pregnancy and Lactation: An Implementation Guide. Washington, DC: National Academy Press. Johnson K., S. F. Posner, J. Biermann, J. F. Cordero, H. K. Atrash, C. S. Parker, S. Boulet and M. G. Curtis. 2006. Recommendations to improve preconception health and health care—United States. A report of the CDC/ATSDR Preconception Care Work Group and the Select Panel on Preconception Care. MMWR Recommendations and Reports 55(RR-6): 1-23. Siega-Riz A. M., L. S. Adair and C. J. Hobel. 1994. Institute of Medicine maternal weight gain recommendations and pregnancy outcome in a predominantly Hispanic population. Obstetrics and Gynecology 84(4): 565-573.